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Hydrogen cycle
Like carbon, nitrogen, and phosphorus, there is also a cycle of hydrogen here on Earth. Hydrogen atoms move between biotic (living) and abiotic (non-living) sources.
Hydrogen (H) is the most abundant element in the universe.
On Earth, common H-containing inorganic molecules include water (H2O), hydrogen gas (H2), methane (CH4), hydrogen sulfide (H2S), and ammonia (NH3).
Organic compounds contain H atoms (as well as C.)
The chemistry of the Hydrogen cycle is highly relevant to the development of life on Earth and mostly likely elsewhere in space.
Hydrogen fuels rockets, but what about power for daily life? We’re getting closer. Phys.Org
Image from, Development and testing of new materials for high temperature PEM water electrolysis, Antonio Luis Tomas-Garcia
Where does our H2 come from? (sources)
biological processes in the oceans
biological (microbial) processes in soils
photochemical production in the troposphere via CH2O also written as H−CHO, formaldehyde.
Where does the H2 go? (sinks)
soil uptake
photochemical destruction in the troposphere by OH radicals
Free H2 can then be consumed by other microbes, oxidized photochemically in the atmosphere, or lost to space.
Cycling: H2 molecules usually exist within the atmosphere for 4 to 7 years before they get taken up in a soil sink.
Hydrogen production and leakage
As we develop hydrogen based industries, in what ways will we be producing, distributing, and using hydrogen? In what ways will hydrogen leak out into the atmosphere?
In the left column we see H2 production.
In the middle column we take into account the fact that once H2 gas is made, it needs to be distributed by trucks, ships, cargo trains, etc.
In the third column we see H2 being used by end-use customers.
Notice that in every step some H2 gas leaks out. Leaks are unintended, and unavoidable. We can minimize them but they will never be zero.
image from, Emission scenarios for a global hydrogen economy
Possible effect on ozone layer
“Increased atmospheric emissions of hydrogen will therefore inevitably lead to increased levels of water vapour in the stratosphere which will in turn lead to increased stratospheric cooling. This cooling may change the distribution of polar stratospheric clouds which play an important role in the formation of ozone holes and hence may delay the recovery of the ozone layer.”
A mitigating factor is that “The potential environmental risks from the hydrogen economy were found to be small in comparison with the environmental benefits. ” …. “the few available studies all point to the impact of large potential hydrogen leakages on the stratospheric ozone layer as being small”
– Hydrogen for Heating: Atmospheric Impacts – A literature review
Possible effect on global warming
Hydrogen gas indirectly acts as a greenhouse gas because it interferes with the global chemical reactions which control the methane levels and the formation of ozone.
Methane and ozone are the second and third most important greenhouse gases after carbon dioxide.
There is still much uncertainty about how much H2 gas would affect global warming, although the effect is currently considered to be very small.
– Hydrogen for Heating: Atmospheric Impacts – A literature review,
Possible effect on air quality
H2 is relatively inert. It offers almost no chemical reactivity with urban pollutants such as NOx, O3, SO2, CO, VOCs and suspended particulate matter. Thus it has no direct influence on urban air quality.
However, because of its reaction with hydroxyl radicals: OH + H2 → H2O + H it plays a weak role in the long-range transport of photochemical ozone. This may affect ozone levels in the lower atmosphere, although the effect is currently estimated to be very small.
Caution in relying on Hydrogen power
Using hydrogen as a source of power for vehicles certainly has its drawbacks—among them the cost and the inefficient use of energy—but researchers are now warning against hydrogen for another reason, The Guardian reports: scarcity and a subsequent dependence on fossil fuels….
“Hydrogen-based fuels can be a great clean energy carrier, yet their costs and associated risks are also great,” said Falko Ueckerdt, at the Potsdam Institute for Climate Impact Research (PIK) in Germany, who led the research.
“If we cling to combustion technologies and hope to feed them with hydrogen-based fuels, and these turn out to be too costly and scarce, then we will end up burning further oil and gas,” he said. “We should therefore prioritise those precious hydrogen-based fuels for applications for which they are indispensable: long-distance aviation, feedstocks in chemical production and steel production.”
The research, published in the journal Nature Climate Change, calculated that producing and burning hydrogen-based fuels in home gas boilers required six to 14 times more electricity than heat pumps providing the same warmth. This is because energy is wasted in creating the hydrogen, then the e-fuel, then in burning it. For cars, using e-fuels requires five times more electricity than is needed than for battery-powered cars.
text above from Researchers Warn Against Becoming Too Dependent On Hydrogen To Power Cars Elizabeth Blackstock, May 2021, Jalopnik
Using hydrogen fuel risks locking in reliance on fossil fuels, researchers warn Damian Carrington, 5/6/2021, The Guardian (UK)
Potential and risks of hydrogen-based e-fuels in climate change mitigation Falko Ueckerdt et al., Nature Climate Change volume 11, pages384–393(2021)
Hydrogen Production and Distribution Alternative Fuels Data Center, US Dept. of Energy,
Some critics of Hydrogen power
The government’s embrace of ‘clean hydrogen’ helps no one but the fossil fuel industry, Richard Denniss, The Guardian , 5/2/2021
External articles
Atmospheric researchers present new findingson the natural hydrogen cycle. CalTech
Assessing Leaks in a Global Hydrogen Infrastructure: Can it Perturb the Natural Hydrogen Cycle?
Leaked hydrogen fuel could have small negative effects on atmosphere
Hydrogen fuel could widen ozone hole
Global Environmental Impacts of the Hydrogen Economy
Hydrogen Effects on Climate, Stratospheric Ozone, and Air Pollution
Impact of a possible future global hydrogen economy on Arctic stratospheric ozone loss, with graphic
What Are The Pros And Cons Of Using Hydrogen To Generate Electricity?
The Hydrogen Hoax , The New Atlantis, by Robert Zubrin
Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
References
Bas van Ruijven et al., Emission scenarios for a global hydrogen economy and the consequences for global air pollution, Global Environmental Change, Volume 21, Issue 3, 2011, Pages 983-994,
Hydrogen for Heating: Atmospheric Impacts – A literature review, BEIS Research Paper Number 2018: no. 21, Dept. for Business, Energy and Industrial Strategy, UK
Learning Standards
Next Generation Science Standards
HS-LS2-4. Use mathematical representations to support claims for the cycling of matter and flow of energy among organisms in an ecosystem.
A Framework for K-12 Science Education Practices, Crosscutting Concepts, and Core Ideas (2012)
LS2.B: Cycles of Matter and Energy Transfer in Ecosystems
College Board Standards for College Success: Science
Standard ES.4 – Cycles of Matter and Energy: Matter on Earth is finite and moves through various cycles that are driven by the transformation of energy
LS.4.1 Matter Cycling – Students understand that matter is continuously recycled within the biological system and between the biological (biotic) and physical (abiotic) components of an ecosystem.
ESH-PE.4.2.2 Construct a graphical representation of the global carbon cycle (or the cycle of some other element or molecule), and use this representation to predict the effects of some environmental change (e.g., evolution of life, tectonic change, human activity) on carbon cycling (or the cycling of some other element or molecule).
Enduring Understanding 3A – Biogeochemical cycles are representations of the transport, transformation and storage of elements on a local, regional or global scale.
Zeroth law of thermodynamics
People normally think of the three laws of thermodynamics. But there is one idea that they all depend on, so basic that it often gets overlooked: the zeroth law.
This idea works like the transitive rule of algebra:
If A = B and B = C then A = C
If the temp of object A = temp of object B,
and the temp of object B = temp of object C,
then the temp of object A = temp of object C
Therefore all three systems would be in thermal equilibrium.
Let’s watch three different materials fulfill this law, by coming into thermal equilibrium.
Animation by Charles Xie
Thermal equilibrium (in this example) is reached when the temp of all pieces = 13.4 degrees C.
http://weelookang.blogspot.sg/2012/09/the-zeroth-law-of-thermodynamics.html
Also see https://www.grc.nasa.gov/www/k-12/airplane/thermo0.html
Another way to view this:
“When body A is placed in thermal contact with body B, there will be a flow of thermal energy between the two bodies. Thermal energy will flow from the body at a higher temperature, to the one at a lower temperature, until thermal equilibrium between the two bodies is reached.”
– Loo Kang Lawrence
Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Measuring mass in the metric system
In science and engineering we often have to make measurements of mass. Now, I understand that a lot of American students have affinity for the traditional English system of measurements.
But we can’t make much progress in any field of science or engineering without first becoming conversant with the metric system. It is used worldwide.
How do we measure mass? To learn practical, hands-on skills, see our lesson here.
Measuring mass with a triple beam balance
But in this lesson we’re going to get a feel what various masses would actually look like in real life.
Kilograms
A kilogram is 1,000 grams. It is abbreviated as kg.
Can we convert between kilograms and pounds…. not quite [TBA]
But if all measurements are done here on Earth then 1 kg of mass has a weight of about 2.2 pounds.
Here’s a 1 kg steak dinner
image from TripAdvisor, Outback Steakhouse, Las Vegas Blvd
How can we visualize this? About the mass of a liter bottle of water or soda.
About the mass of good size hardcover book. About the mass of a quart of Gatorade.
Or about the mass of an adult Black-Footed Ferret.
Grams
A metric unit of mass is the gram abbreviated as g.
What kind of things are about a gram in mass?
Centigrams
Centi means 1/100th 0.01 10-2
A smaller metric unit of mass is the centigram abbreviated as cg.
It is one one-hundredth of a gram.
What kind of things are about a cg in mass? Many medications come in 1 cg size, although they more often are measured as 100 mg. Here are magnesium supplement pills.
When a pencil tip breaks, a bigger piece could be about 1 cg.
(We could name something that has a mass of gram and divide it in ten pieces)
milligrams
milli means 1/1000th 0.001 10-3
This is 1/1000th of a gram.
What kind of things are commonly measured in milligrams?
Many doses of medications are measured in milligrams:
Amitriptyline (Elavil) treats chronic pain and depression.
Atorvastatin (Lipitor) treats high cholesterol.
Amlodipine (Norvasc) treats high blood pressure and angina.
Here is crushed powder of a medication shown next to a penny for comparison.
Penny, 1 mg, 10 mg, 25 mg
Micrograms
Yet even smaller is the microgram abbreviated as μg
micro means 1/1,000,000th 0.000001 10-6
Just one one-millionth of a gram
What kind of things are commonly measured in micrograms?
Grains of sand are around 30 to 50 micrograms.
Mass of a grain of sand
Nanograms
Abbreviated as ng.
nano means 1/1,000,000,000 th 0.000000001 10-9
Imagine cutting a raisin into a billion pieces. Each of those tiny pieces has a mass of about one ng.
What kind of things are about a nanogram in mass?
A human cell or a grain of birch pollen. Note that in this picture, each dot that you can see is likely dozens of pollen grains stuck together.
Each individual grain by itself is so small that you’d need a microscope to clearly see it.
Nanograms are very small compared to anything we see in our daily lives, but they are large compared to a single atom
Chemistry math & mass problem
How many atoms of iron (Fe) are in 1 ng (1.0 x 10-9 g) of iron?
This problem from xaktly – Chemistry – The Mole.
We start by finding the molar mass of iron from the periodic table. It’s 55.85 g/mol.
We use the molar mass to convert to moles.
Then multiply by 6.022 x 1023 atoms per mole to get the number of atoms.
1 ng of iron atoms is about 1 x 10 ^ 13 atoms!
That’s 10,000,000,000,000 atoms.
Videos
Powers of Ten and the Relative Size of Things in the Universe
Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Computer apps
Powers of Ten (JAVA) For Windows and Macs. Check to see if this runs on Android phones or Chromebooks.
Secret Worlds: The Universe Within: Molecular Expressions
The size and scale of the universe
htwins.net – scale of the universe
Smartphone and tablet apps
Cosmic Zoom app by Tokata. For Android and iPad
Google Play Store link
About cozmic zoom
Powers of Minus Ten, by Dynamoid Apps. iPad app
thepartnershipineducation.com Powers-of-minus-ten
Link for the Apple app store
Learning Standards
Massachusetts Science and Technology/Engineering Curriculum Framework
Science and Engineering Practices: 5. Using Mathematics and Computational Thinking: Apply ratios, rates, percentages, and unit conversions in the context of complicated measurement problems involving quantities with derived or compound units (such as mg/mL, kg/m 3, acre-feet, etc.).
National Council of Teachers of Mathematics
Students need to develop an understanding of metric units and their relationships, as well as fluency in applying the metric system to real-world situations. Because some non-metric units of measure are common in particular contexts, students need to develop familiarity with multiple systems of measure, including metric and customary systems and their relationships.
National Science Teachers Association
The efficiency and effectiveness of the metric system has long been evident to scientists, engineers, and educators. Because the metric system is used in all industrial nations except the United States, it is the position of the National Science Teachers Association that the International System of Units (SI) and its language be incorporated as an integral part of the education of children at all levels of their schooling.
Sunrise Sunset The science and culture
One of the goals of science education is to see how just a handful of basic laws of nature allow us to understand all phenomenon in our physical universe, from the simplest examples (how objects move) to the most complex (how planets orbit stars)
One of the goals of Social Studies is to expose students to the diversity of ethnic, religious, and cultural observances in our world. The College, Career, and Civic Life (C3) Framework for Social Studies State Standards notes that students should be able to describe how religions are embedded in culture and cannot only be isolated to the “private” sphere, and identify which religious communities are represented or obscured in public discourse.
Science and social studies teachers can work together to create multi-disciplinary units. Here is one on sunset, also known as sundown The daily disappearance of the Sun below the horizon due to Earth’s rotation is something that needs to be understood scientifically, and has ties to major world cultures.
(This section has been adapted from Sunset, Wikipedia)
The time of sunset is defined in astronomy as the moment when the upper limb of the Sun disappears below the horizon.
Near the horizon, atmospheric refraction causes sunlight rays to be distorted to such an extent that geometrically the solar disk is already about one diameter below the horizon when a sunset is observed.
Sunset is distinct from twilight, which is divided into three stages:
civil twilight, begins once the Sun has disappeared below the horizon, and continues until it descends to 6 degrees below the horizon
nautical twilight, between 6 and 12 degrees below the horizon
astronomical twilight, when the Sun is between 12 and 18 degrees below the horizon.
Dusk = very end of astronomical twilight, the darkest moment of twilight just before night.
Night occurs when the Sun reaches 18 degrees below the horizon and no longer illuminates the sky.
image by TWCarlson from Wikimedia.
Refraction: Appearances versus reality
We actually see the Sun a few minutes before it rises and a few minutes after it sets. This is due to the fact that the Earth’s atmosphere refracts the rays of light from the sun.
We learn about refraction of light in our section on geometric optics.
Looking at the situation from the side:
Standing at the beach, looking out towards the horizon, we would see this:
When sun just disappears, the center of the sun is 56’ below. the horizon (almost one degree!). What you see. True position. 34.5’ True position. What you see. 34.5’ 56’ Moment of sunset. Height = 0.
This image from Latitude and Longitude powerpoint by Darleen Cross.
Refraction of light is the reason for mirages – the naturally occurring phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky.
Here’s a spectacular mirage (magnified) that was seen at the Scottish Open golf tournament in Aberdeen, 2014.
Cultural connections
The significance of sunrise and sunset in cultures around the world:
Jewish
In Jewish culture the precise time of sundown and sunrise is of practical and religious importance.
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Observant Jews pray three times daily, and the first prayer service occurs after sunrise, and the last prayer service must occur before the next one.
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Observance of Shabbat, the Jewish Sabbath, is considered to be one of the most important ethical-ritual practices in Judaism. In order to safeguard its observance the timing of sundown should be known as precisely as possible. To avoid any possible violations of Sabbath laws, observance of the Sabbath begins a number of minutes before this time.
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Observance of Jewish festivals, such as Passover, Sukkot, and Shavuot, begin at nightfall. This is why people commonly say that “Jewish holidays begin on the evening of the day before.”
Daybreak עֲלוֹת הַשַּׁחַר alot ha’shachar) – when the first rays of light are visible in the morning
Sunrise הַנֵץ הַחַמָּה, hanetz ha’chamah – when the entire disc of the sun appears over the horizon.
Sunset שְׁקִיעַת הַחַמָּה, shkiyat ha’chamah – when the disc of the sun falls below the horizon
Twilight – bein ha’shemashot בֵּין הַשְּׁמָשׁוֹת, (between the suns) – the period between sunset and nightfall. The status of this time was never clearly delineated in traditional Jewish law. Therefore, on the Sabbath, festivals, and fast days the stringencies of both the previous and following days usually apply.
Muslim
This section is excerpted from a discussion at Islam.stackexchange.com
During the time of the prophet, as was also the case in the Hebrew world and in pre-Islamic Arabia, the day was not calculated as a twenty-four hour period starting at midnight (as our current system of time does). Rather, each day would marked at sunset, and would consist of two parts, starting with “Night” (ليل) and proceeding to “Day” (نهار).
The Qur’an itself does not define “night” clearly; while there are many references associating “day” with the sun and brightness and associating “night” with darkness and concealment, the exact delineation between the two is not so precise.
In fact, according to the classical text الجامع لأحكام القرآن, Imam Qurtubi claims that God alone knows the exact measure of night, based on the revelation in Surat Al-Muzzammil that “Allah determines the night and the day” (الله يقدر الليل والنهار).
According to Lane’s Lexicon, ليل and نهار are opposites, with no intervening period between them. Day, being defined as “the time from the rising of the dawn to sunset”, would thus perfectly complement night, which would by extension be defined as the time from sunset to the rising of the dawn (i.e. sunset to Fajr).
Similarly, Brill’s Encyclopedia of the Qur’an considers the night to include everything from the “evening twilight” (شفق) until “the breaking of morning” (سحر), which immediately precedes the dawn (فلق) itself.
Surat al-Baqarah regulates the nights of fasting until “the white thread of dawn is distinct from the black thread” (يتبين لكم الخيط الأبيض من الخيط الأسود من الفجر), which correlates strongly with the above definitions.
It is important to note that, colloquially, the word ليل (night) can also be overloaded in a similar manner to the English “day”, wherein it can be used to refer to an entire 24-hour period (more accurately, an entire period from sunset to sunset) rather than the night-time in particular. The intended meaning is usually clear in context, especially when ليل is used in a pluralized form, but this too needs to be kept in mind.
While there has been significant scholarly interest in the exact definitions of night and day, especially in regards to the transitory periods of twilight and dawn, much of this research was not conducted until significantly after the death of the prophet himself. As such, any references to “night” in the hadith literature were not necessarily (or likely) using the the term in any scientifically precise manner.
Hindu
(TBA)
Native American
(TBA)
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Thanks for reading. While you’re here see our other articles on astronomy, biology, chemistry, Earth science, mathematics, physics, the scientific method, and making science connections through books, TV and movies.
Learning Standards
National Curriculum Standards for Social Studies
3. People, Places, and Environments
The study of people, places, and environments enables us to understand the relationship between human populations and the physical world. Students learn where people and places are located and why they are there. They examine the influence of physical systems, such as climate, weather and seasons, and natural resources, such as land and water, on human populations….
During their studies, learners develop an understanding of spatial perspectives, and examine changes in the relationship between peoples, places and environments….
8. Science, Technology, and Society
Science, and its practical application, technology, have had a major influence on social and cultural change, and on the ways people interact with the world….
There are many questions about the role that science and technology play in our lives and in our cultures. What can we learn from the past about how new technologies result in broader social change, some of which is unanticipated?… How can we preserve fundamental values and beliefs in a world that is rapidly becoming one technology-linked village? How do science and technology affect our sense of self and morality?
College, Career, and Civic Life (C3) Framework for Social Studies State Standards
College, Career, and Civic ready students:
D2.Rel.4.9-12: Describe and analyze examples of how religions are embedded in all aspects of culture and cannot only be isolated to the “private” sphere.
D2.Rel.12.9-12: Identify which religious individuals, communities, and institutions are represented in public discourse, and explain how some are obscured.
Next Generation Science Standards
5-ESS1-2 Earth’s Place in the Universe
5-ESS1-2. Represent data in graphical displays to reveal patterns of daily changes in length and direction of shadows, day and night, and the seasonal appearance of some stars in the night sky.
NGSS Evidence Statements – Observable features of the student performance: Using graphical displays (e.g., bar graphs, pictographs), students organize data pertaining to daily and seasonal changes caused by the Earth’s rotation and orbit around the sun. Students organize data that include:
i. The length and direction of shadows observed several times during one day.
ii. The duration of daylight throughout the year, as determined by sunrise and sunset times.
iii. Presence or absence of selected stars and/or groups of stars that are visible in the night sky at different times of the year.
NSES (National Science Education Standards)
Content Standard D – Earth and Space Science: Earth in the Solar System
Grades 5-8, page 160. Most objects in the solar system are in regular and predictable motion. Those motions explain such phenomena as the day, the year, phases of the moon, and eclipses.
The Wave Nature of Matter
Everything is made of particles. Pieces of solid matter. All solids, liquids, and gases – you name it. Dirt, pebbles, and red blood cells. Trees, dust mites, planets, and even the air we breath.
That’s obvious and common sense. We even make models of atoms and molecules with wood or plastic manipulatives like this, so that must mean something, right?
Except… we’re going to learn that all solid particles in the universe have a wave-like behavior.
And oh yes, all wave-like behavior has particle-like behavior?! Yup. For real.
This is the inescapable – and verified – result of the quantum mechanical nature of our world.
In the late 19th and early 20th century, when physicists asked hard questions about matter, they came across unexpected, extraordinary results.
We basically went through Alice’s Looking Glass – into the quantum realm. A realm where all particles have wave-like qualities. And further, all waves have particle-like qualities.
To be clear, none of this is a metaphor – we’re being quite literal.
The classical model of matter
The old model of the atom, and of everything in the universe was classical:
Everything is made of solid matter.
Everything has a definite position, mass, and velocity, at any moment in time.
Everything has a definite momentum at any moment in time.
How could it not? That seems to be true by definition.
We envisioned that there was a positively charged nucleus in the center of atoms.
Electrons (hence e– ) orbited around the nucleus like planets orbit around a start.
And so was everything else in our universe. People, cars, rocks, planets, and stars.
But when we looked more closely at their behavior, we kept seeing evidence that this model couldn’t be correct.
The classical model of atoms was wrong
e– lose energy by giving off photons (particles of light)
e– gain energy by absorbing a photon (and its energy)
If e– behaved like solid objects then they could move to any position (further from nucleus, or closer.)
They should be able to have any amount of energy: From a little to a large amount – and any value in between.
Therefore, when atoms gave off light, it was when e– dropped from one energy level to another.
If e– e could exist at any level then they could emit any energy of light, any color.
Thus atoms should be able to produce a continuous spectrum. Continuous means “all possible colors, smoothly going from one to the next, with no gaps.” Like this:
But experiments always showed otherwise! When individual atoms absorb light (energy) they only absorb photons (particles of light) in certain wavelengths. Yet they never absorb energy in others? How is that possible?
And when individual atoms emit (give off) light (energy), they only give off photons in certain wavelengths, never any others. Again, how is this possible?
No one could come with up with any model of the atom which was consistent with classical physics.
By 1913 Niels Bohr realized that nature was telling us something: Our classical intuition about what an atom was, was simply wrong.
We were forced to listen to what nature was telling us. Out of almost desperation, Bohr listened to nature and created a new, semi-classical model of the atom:
Like the old model, Bohr’s model portrays atoms as having a nucleus in the center and e– orbiting around it.
But in his new model e– could only exist in orbits of a certain radius. Not in any others.
Sure, they could lose energy, and “fall” from one orbit to a lower orbit – yet they didn’t exist anyplace in between?!
It was like they disappeared from kind of orbit – and reappeared in a different one?!
Quantum jumps
In classical physics any orbit is possible. It doesn’t make sense that only some orbits would be “allowed.”
Think of climbing a ladder. You can climb up from one stair to the next stair… and in doing so you obviously must pass all of the positions in-between.
There are an infinite number of positions between one ladder rung and the next. We don’t just disappear at one rung and then appear up at the next one, right?
(This GIF might be by artist Daniela Sherer)
This guy climbing the ladder, above, shows the classical, normal world we know.
We’re at one place, then at another – but only because we pass through every position in between.
The same thing goes for a car driving down the road. It starts at one place, ends up at another – and by definition the car must pass through every position in between.
But now imagine seeing this: the car literally disappears from the universe at one place, and then reappears in another place further down the road.
Animation by RK
Without ever being in any of the positions in between?! That’s not possible, right?
Except – that is precisely what e– in atoms seem to do.
Worse, all sub-atomic particles have this quantum leap type of behavior.
This violates common sense. But here’s the kicker – when we look closely, this is how the universe works.
Bohr’s model of the atom
An e– gives off energy in the form of a photon. Photon shown as green squiggly arrow.
Then the e– disappears from where it was and reappears in a lower orbit – without traveling through any position in-between!
Later, the e– absorbs energy from a different photon (another green squiggly arrow.)
Once it absorbs the energy the e- jumps up to a higher orbit – again, without traveling through any of the position in between.
These seemingly impossible jumps are called quantum leaps.
(FYI, e- do not actually circular orbits. Bohr’s model was just the first approximation)
(image Bohr atom animation.gif)
This model was the beginning quantum mechanics.
From the Bohr model to the wave model
The following Socratic-style discussion comes from Physics 2000.
Why should an electron’s angular momentum have only certain values?
Why do electrons emit or absorb radiation only when they jump between energy levels?
Bohr’s theory fits experimental results, but it doesn’t explain why atoms behave the way they do.
In 1923, about ten years after Bohr published his results, Louis de Broglie came up with a fascinating idea to explain them: all matter, he suggested, actually consists of waves.
At first, de Broglie had no idea what he meant by matter being “waves.” It was just a mathematical construct that was helpful.
It was only later that physicists realized that this mathematical construction was telling us something about the true nature of reality itself!
de Broglie’s wave model of particles explains why an electron can only be in certain orbits!
de Broglie’s wave model assumes that any particle – an electron, atom, bowling ball, whatever – had a “wavelength”
Yeah, that’s weird – but let’s just roll with it for the moment.
Why assume such a thing? This assumption wasn’t arbitrary; de Broglie knew that the momentum and wavelength of a photon actually were related.
Hmm, wait a minute…photons don’t have any mass, do they? How can photons have momentum?
Photons don’t have mass, but they do have energy – and as Einstein famously proved, mass and energy are really the same thing.
So photons do have momentum – but what exactly is a photon?
For centuries, a heated debate went on as to whether light is made up of particles or waves.
In some experiments, like Young’s double slit experiment, light clearly showed itself to be a wave.
But other phenomena, such as the photoelectric effect, demonstrated equally clearly that light was a particle.
So which is it? Well, sort of both – or better, it is neither.
Light is a thing that sometimes has particle-like behavior, and sometimes has wave-like behavior.
It all depends on what sort of experiment you’re doing.
This is known as wave/particle duality. Like it or not, physicists have been forced to accept it.
That’s why we sometimes talk about “electromagnetic waves” and sometimes about “photons.”
de Broglie’s big idea was that maybe it’s not just light that has this dual personality; maybe it’s everything!
All right…let’s say I accept this idea. How does it explain Bohr’s energy levels?
If we think of electrons as waves, we change our whole concept of what an “orbit” is.
Instead of having a particle whizzing around the nucleus in a circular path, we’d have a wave existing around the whole circle.
Now, the only way that such a wave could exist is if the wave has constructive interference.
It has to have a whole number of its wavelengths fit exactly around the circle.
If the circumference is exactly as long as two wavelengths, say, or three or four or five, that’s great, but two and a half wavelengths won’t cut it.
If we have fractional amounts of wavelengths then there is destructive interference, and the waves cancel out.
So there could only be orbits of certain sizes, depending on the electrons’ wavelengths –which depend on their momentum.
Apps: Modeling electrons with standing waves
Standing waves in Bohr’s atomic model
Standing waves in Bohr’s atomic model Geogebra.org
How to run CDF demonstrations: worlds of math & physics
Seeing constructive & destructive wave interference in 3 dimensions with DESMOS
More from Physics 2000
Student: But is this just some mathematical trick that happens to work, or do particles actually behave like waves sometimes?
Teacher: They actually do behave like waves! Just a few years after de Broglie published his hypothesis, several experiments were done proving that electrons really do display wavelike properties.
Student: So how come when I look at a bowling ball, I don’t notice it acting in a wavelike manner? You said that everything is affected by wave/particle duality.
Teacher: Think about what the wavelength of the bowling ball would be. According to de Broglie, the wavelength is equal to Planck’s constant divided by the object’s momentum.
Planck’s constant is very, very, very tiny, and the momentum of a bowling ball, relatively speaking, is huge.
If you had a bowling ball with a mass of, say, one kilogram, moving at one meter per second, its wavelength would be about a septillionth of a nanometer.
This is so ridiculously small compared to the size of the bowling ball itself that you’d never notice any wavelike stuff going on.
That’s why we can generally ignore the effects of quantum mechanics when we’re talking about everyday objects.
It’s only at the molecular or atomic level that the waves begin to be large enough (compared to the size of an atom) to have a noticeable effect.
Student: If electrons are waves, then it kind of makes sense that they don’t give off or absorb photons unless they change energy levels.
If it stays in the same energy level, the wave isn’t really orbiting or “vibrating” the way an electron does in Rutherford’s model, so there’s no reason for it to emit any radiation.
And if it drops to a lower energy level… let’s see, the wavelength would be longer, which means the frequency would decrease, so the electron would have less energy.
Then it makes sense that the extra energy would have to go someplace, so it would escape as a photon–and the opposite would happen if a photon came in with the right amount of energy to bump the electron up to a higher level.
Teacher: Very good! Now we can look at how Schrödinger extended de Broglie’s idea of waves into a whole new model for the atom…
What happened next, to finally create Quantum Mechanics, was that Schrödinger extended de Broglie’s idea of waves into a whole new model for the atom.
Related apps
Models of the Hydrogen Atom – PhET
Run this PhET app. Click to change from Experiment to Prediction. Press button to start the electron gun.
Under ‘Atomic model,’ the models of the atom most pertinent to this lesson are the Bohr model and the de Broglie model.
External resources
astronomy.nmsu.edu/agso/spectroscopy.pdf
Continuous spectra vs actual spectra
Emission Spectra: How Atoms Emit and Absorb Light
Emission and absorption spectra
Spectral Classification of Stars
Formation of Spectral Lines, Lumen
Physics 2000. University of Colorado by Prof. Martin V. Goldman. This website no longer exists except as an archived copy.
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Maxwell’s Equations
Introduction
On Quora, Mark Eichenlaub writes –
The history of electromagnetism is one of unification. Over and over, different ideas about how things work were subsumed into the same theoretical framework…. Electromagnetism is an example of a field theory, the central object of study in theoretical physics.
A “field” means that at any point in space and time, there’s an electric and magnetic vector there. These fields pervade all of space – they are in the room around you right now, and in outer space, even within you…
We don’t have a mechanical picture of what the field is, or why it is a certain way. It’s not like waves in the water or anything like that. It just exists, but we do have mathematical rules that describe how it works….
Michael Faraday investigated things like the way a wire carrying electric current deflects a compass needle. His crowning achievement was to discover that changing magnetic fields create electric fields, a phenomenon called induction.
James Clerk Maxwell looked at all that, sat down with pen and papers, and mathematically described Faraday’s results in a complicated set of differential equations, importantly including the idea that changing electric fields would create magnetic fields, completing the symmetry between the two.
When Maxwell finished his theory, he discovered that it allowed waves of electromagnetism to fly off at high speed – when he calculated the speed, it turned out to be the speed of light.
Experiments with radio waves soon verified that light was nothing more than a special form of electricity and magnetism.
You can think of it as if we had been studying the way hot air balloons and airplanes and things work, and so were thinking about the dynamics of air. In the process, we develop equations for air, and figure out that sound is just waves moving through the air.
The theory of sound and the theory of airplanes are actually the same theory, even though they don’t seem very similar. That’s roughly what happened for light, except that unlike for sound, no one expected it. (Or at least it wasn’t obvious beforehand.)
Maxwell’s equations describe how electric and magnetic fields work, but those fields need to interact with matter – that happens via electric charge. Charge is an innate property of matter…
Fields
We keep talking about the electromagnetic field. What exactly is a “field” anyways? See What are fields?
Our articles
Maxwell’s equations (our main article, for now)
Backup: Get to know Maxwell’s Equations
External articles
Get to Know Maxwell’s Equations—You’re Using Them Right Now, Wired
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Universal Design for Learning (UDL)
UDL is a design framework for providing increased access and reduced barriers to learning.
UDL encourages us to be intentional in our design without adding excessive demands on faculty. Many of us are already implementing good teaching practices that are the basis of universal design.
UDL can involve high-tech, low-tech and no-tech strategies.
Image by Gerd Altmann, Pixabay, Free for commercial use
Engagement – motivating students
Offer both group and individual work
Engage in-class and online
Allow students to select topics within a given assignment that is based on their interest and relevancy
Presenting information
Offer visual and auditory (text, video, visuals, infographics) works
Provide clear, detailed directions and instructions with rubrics and examples
Record lectures for review after class
Ways to demonstrate learning
Offer flexibility and choice in ways in which students demonstrate learning outcomes (e.g. presentation, essay, show step-by-step problem solving on a whiteboard, etc.)
Provide opportunities for feedback and revision of work
Increase amount of “low stakes” assignments
How teachers transform these ideas into action
Scaffolding: Making the standard curriculum and assignments more accessible.
* study guides
* tapping into student’s prior knowledge
* many opportunities to ask questions
* frontloading selected vocabulary
* relating ideas with analogies and visualizations
* Clear instructions and expectations.
* Frequent checks for understanding
* Have students use interactive apps
* Guided notes
* Graphic organizers
* Showing students how to color code notes, diagrams, etc.
* Historical, cross-curricular connections
* Recording lectures so students can review it later.
Differentiation: Providing a different level of curriculum and assignments. We adapt the topics covered to suit a student’s processing speed and ability.
* Text-to-speech (computer reads aloud documents to students)
* Speech-to-text (student dictates words and the computer writes them in a document.)
* Material from alternative textbooks. Offer a reduced wordcount and embedded vocabulary support for reluctant or struggling readers.
* Use a teacher-developed website: Utilize step-by-step explanations, color graphics, and interactive apps from a variety of sources.
* Shorter homework assignments.
* extra time for assignments
* Mastery grading
* Offer option for units to be self-paced.
* Replace traditional written lab directions with less text and more step-by-step diagrams/drawings.
Provide multiple ways for a student to show what they have learned
Draw – create a comic strip to show a process.
Create a PowerPoint (or Google Slide presentation)
Record a podcast or video (easy with iPads or Chrome extensions like Screencastify)
Create a commercial or skit
Create a concept map
For mathematics and physics problem-solving, it is essential for students to understand and use mathematical equations, and to use and create carefully labelled diagrams. Traditionally students use a pencil, paper, and calculator to do such work, fully writing out solutions on a sheet of paper. This process can be adapted for special education. I will write up a section on how this can be done in a physics class.
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Fun books to inspire science teachers as well as students
Fun books to inspire science teachers as well as students
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Gonzo Gizmos: Projects and Devices to Channel Your Inner Geek, by Simon Quellen Field
Step-by-step instructions to building more than 30 fascinating devices …e.g. how to construct a simple radio with a soldering iron, a few basic circuits, and three shiny pennies. Instructions are included for a rotary steam engine that requires a candle, a soda can, a length of copper tubing, and just 15 minutes. To use optics to roast a hot dog, no electricity or stove is required, just a flexible plastic mirror, a wooden box, a little algebra, and a sunny day. Also included are experiments most science teachers probably never demonstrated, such as magnets that levitate in midair, metals that melt in hot water, a Van de Graaff generator made from a pair of empty soda cans, and lasers that transmit radio signals.
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Physics, Fun, and Beyond: Electrifying Projects and Inventions from Recycled and Low-Cost Materials, by Eduardo de Campos Valadares
Build more than 110 projects that uncover the physics beneath everyday life! Most o are amazingly easy to build: all you’ll need are your everyday household tools and cheap (sometimes free) materials.
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Why Toast Lands Jelly-Side Down: Zen and the Art of Physics Demonstrations, by Robert Ehrlich
A collection of physics demonstrations that prove that physics can, in fact, be “made simple.” Intentionally using low tech and inexpensive materials from everyday life, Why Toast Lands Jelly-Side Down makes key principles of physics surprisingly easy to understand. After laying out the basic principles of what constitutes a successful demonstration, Ehrlich provides more than 100 examples.
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The Prism and the Pendulum: The Ten Most Beautiful Experiments in Science, by Robert Crease
We see the first measurement of the earth’s circumference, accomplished in the third century B.C. by Eratosthenes using sticks, shadows, and simple geometry. We visit Foucault’s mesmerizing pendulum, a cannonball suspended from the dome of the Panthéon in Paris that allows us to see the rotation of the earth on its axis. We meet Galileo – the only scientist with two experiments in the top ten – brilliantly drawing on his musical training to measure the speed of falling bodies. And we travel to the quantum world, in the most beautiful experiment of all.
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How Things Work: The Physics of Everyday Life, by Louis A. Bloomfield
Uses familiar objects to introduce basic physics concepts with real-life examples. For example, discussions of skating, falling balls, and bumper cars are included to explain the laws of motion. Air conditioners and automobiles are used to explore thermodynamics.
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The Way Things Work Now, by David Macaulay
Explainer-in-Chief David Macaulay updates the worldwide bestseller The New Way Things Work to capture the latest developments in the technology that most impacts our lives. Famously packed with information on the inner workings of everything from windmills to Wi-Fi, this extraordinary and humorous book both guides readers through the fundamental principles of machines, and shows how the developments of the past are building the world of tomorrow.
This sweepingly revised edition embraces all of the latest developments, from touchscreens to 3D printer…. What possible link could there be between zippers and plows, dentist drills and windmills? Parking meters and meat grinders, jumbo jets and jackhammers, remote control and rockets, electric guitars and egg beaters? Macaulay explains them all.
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Building Big, by David Macaulay
Why this shape and not that? Why steel instead of concrete or stone? Why put it here and not over there? These are the kinds of questions that David Macaulay asks himself when he observes an architectural wonder. These questions take him back to the basic process of design from which all structures begin, from the realization of a need for the structure to the struggles of the engineers and designers to map out and create the final construction. Macaulay engages readers’ imaginations and gets them thinking about structures they see and use every day — bridges, tunnels, skyscrapers, domes, and dams.
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Insultingly Stupid Movie Physics: Hollywood’s Best Mistakes, Goofs and Flat-Out Destructions of the Basic Laws of the Universe, b y Tom Rogers
Would the bus in Speed really have made that jump? -Could a Star Wars ship actually explode in space? -What really would have happened if you said “Honey, I shrunk the kids”? The companion book to the hit website (www.intui tor.c om/moviephy sics), which boasts more than 1 million visitors per year, Insultingly Stupid Movie Physics is a hilarious guide to the biggest mistakes, most outrageous assumptions, and the outright lunacy at work in Hollywood films that play with the rules of science.
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Don’t Try This At Home!: The Physics of Hollywood Movies, by Adam Weiner
A fresh look at the basics of physics through the filmmaker’s lens. It will deconstruct, demystify, and debunk popular Hollywood films through the scientific explanations of the action genre’s most dynamic and unforgettable scenes.
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The Cosmic Code: Quantum Physics as the Language of Nature, Heinz R. Pagels
One of the best books on quantum mechanics for general readers. Heinz Pagels, an eminent physicist and science writer, discusses the core concepts without resorting to complicated mathematics. He covers the development of quantum physics. And although this is an intellectually challenging topics, he is one of the few popular physics writers to discuss the development and meaning of Bell’s theorem. Anecdotes from the personal documents of Einstein, Oppenheimer, Bohr, and Planck offer intimate glimpses of the scientists whose work forever changed the world.
A reviewer on Goodreads notes – “Pagels assumes a lay audience, but one prepared, after single paragraphs of description, to thereafter carry the technical terms across the finish line. Unlike other popsci, he also favors technical description–albeit written in smooth, clear prose over metaphor… The commitment to not talking down to his audience is rather commendable…
[His] intellectual project [is] reconciling the impossibility of visualizing quantum processes with a remit to communicate the science to non-scientists who, lacking the requisite mathematical literacy, necessarily require metaphor, universal human logics, and everyday comparisons to grasp most science in the first place.”
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Quantum Reality: Beyond the New Physics, Nick Herbert
Herbert brings us from the “we’ve almost solved all of physics!” era of the early 1900s through the unexpected experiments which forced us to develop a new and bizarre model of the universe, quantum mechanics. He starts with unexpected results, such as the “ultraviolet catastrophe,” and then brings us on a tour of the various ways that modern physicists developed quantum mechanics.
And note that there isn’t just one QM theory – there are several! Werner Heisenberg initially developed QM using a type of math called matrix mechanics, while Erwin Schrödinger created an entirely different way of explaining things using wave mechanics. Yet despite their totally different math languages – we soon discovered that both ways of looking at the world were logically equivalent, and made the same predictions. Herbert discussed the ways that Paul Dirac and Richard Feynman saw QM, and he describes eight very different interpretations of quantum mechanics, all of which nonetheless are consistent with observation…
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In Search of Schrödinger’s Cat: Quantum Physics and Reality, John Gribbon
“John Gribbin takes us step by step into an ever more bizarre and fascinating place, requiring only that we approach it with an open mind. He introduces the scientists who developed quantum theory. He investigates the atom, radiation, time travel, the birth of the universe, superconductors and life itself. And in a world full of its own delights, mysteries and surprises, he searches for Schrodinger’s Cat – a search for quantum reality – as he brings every reader to a clear understanding of the most important area of scientific study today – quantum physics.”
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The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory, Brian Greene
“Brian Greene, one of the world’s leading string theorists, peels away the layers of mystery surrounding string theory to reveal a universe that consists of eleven dimensions, where the fabric of space tears and repairs itself, and all matter—from the smallest quarks to the most gargantuan supernovas—is generated by the vibrations of microscopically tiny loops of energy….
Today physicists and mathematicians throughout the world are feverishly working on one of the most ambitious theories ever proposed: superstring theory. String theory, as it is often called, is the key to the Unified Field Theory that eluded Einstein for more than thirty years.
Finally, the century-old antagonism between the large and the small-General Relativity and Quantum Theory-is resolved. String theory proclaims that all of the wondrous happenings in the universe, from the frantic dancing of subatomic quarks to the majestic swirling of heavenly galaxies, are reflections of one grand physical principle and manifestations of one single entity: microscopically tiny vibrating loops of energy, a billionth of a billionth the size of an atom.”
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How can we see photos taken in UV, Infrared or Radio?
How is it possible that we can see photos taken in UV, Infrared or Radio?
Humans can only see visible wavelengths of light. Visible light has 𝜆 (wavelengths) of about 380 to 700 nm (nanometers.)
Yet in science class we often see infrared photos, like this!
Or we see photos taken in ultraviolet light. Bees see UV light, and so see flowers differently than we do. On the left is a primrose in visible light, but on the right we see it in UV light.
We see radar images of the Earth from an orbiting satellite, or radio telescope images of the galaxy. And those wavelengths of light just aren’t visible to humans.
UV light 𝜆 = 100 to 400 nm.
Infrared light 𝜆 = 700 nm to 1 mm
Radio waves 𝜆 = 1 millimeter to 100 kilometers.
Okay, the easy part is the technology: we can build equipment that detect such wavelengths. But what is the resulting image that we are looking at? Something visible to the human eye – which is in the visible spectrum.
So what does it even mean to translate something invisible to something visible?
Think about transposing music on a piano. We can play a melody in the middle of a piano keyboard. Then we can play the exact same melody one octave higher just by moving our hands to the right. We can do this again, and again. Each time the same melody is preserved, just an octave higher.
We can keep doing this until the notes are so high pitched that human ears can’t detect them (although maybe dogs and bats could hear this.) The resulting melody would be the same as the original melody, yet undetectable to us.
We can compare this to “seeing” higher frequencies of light – they get higher and higher until they become ultraviolet or X-rays.
Now, we can do the same thing again, but in reverse. Play a melody in the middle of a piano keyboard. Then we can play the exact same melody one octave lower just by moving our hands to the left. We can do this again, and again. Each time the same melody is preserved, just an octave lower.
We can keep doing this until the notes have such a low pitch that human ears can’t detect them (although whales, elephants, and hippopotamuses could hear this.) The resulting melody would be the same as the original melody, yet undetectable to us.
This is pretty much what is happening when we print out images of data capturing UV, Infrared or Radio!
For high frequency images (like UV light) we are dropping the image by many octaves (so to speak) until we reach the visible spectrum.
For low frequency images (like radio or infrared) we are increasing the image by many octaves (so to speak) until we reach the visible spectrum.
Avoiding misunderstandings
Electromagnetic waves (light, UV, radio) are transverse waves. The direction of particle displacement is perpendicular to the direction of movement.
Sound waves are longitudinal waves.
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How do we know how atoms are arranged in a crystal?
How do we know how atoms are arranged in a protein, an enzyme, or a fat molecule?
Each individual atom is only a few nanometers (1 x 10-10 m) wide, way too small to photograph directly.
Yet we often see images of how atoms how are arranged, like this.
Just look it this image: We see individual atoms (yellow, red, blue) connected in a precise pattern. How in the world did we see this?
Well, there’s no way to see this, in one step. Too difficult.
But there is a way to accurately visualize this, if we go through a very careful process.
The process is called X-ray crystallography.
We start with a tiny sample of whatever it is we’d like to learn about. For example, a protein or an enzyme.
First, a biochemist needs to purify cells, and extract just the one molecule that we’re interested in.
That, in of itself, is a procedure that needs to be done carefully.
Once we have a pure form of that molecule, we then crystallize it.
Of course, in order for the rest of this lesson to make sense, we need to know what a “crystal” really is. So if you haven’t already learned about this, first check out our lesson on What is a crystal?
Short version: A crystal is solid material, in which the atoms, molecules, or ions are arranged in an orderly repeating pattern.
For instance, on the left is the atom-by-atom structure of a halite crystal.
(Purple is sodium ion, green is chlorine ion.)
This crystal is so tiny, that it would take 10,000 of them to make one tiny grain of salt!
On the right is a visible salt crystal. This contains millions of such crystal units.
Well, if we have a pure chemical from a cell (protein, enzyme, fatty acid, etc.) we can slowly cool and dry this chemical until it crystallizes!
Each different kind of molecule would create a differently shaped and colored crystal.
Please understand that these crystals look tiny – maybe just 1/10 of an inch across.
Yet each crystal contains millions of repeating atomic units.
Figure 22.3. Examples of protein crystals. From left to right: β-secretase inhibitor complex; human farnesyl pyrophosphatase in complex with zoledronic acid; abl kinase domain in complex with imatinib; cdk2 inhibitor complex.
Source – Jean-Michel Rondeau, Herman Schreuder, in The Practice of Medicinal Chemistry (Fourth Edition), 2015
This crystal is then placed in front of an X-ray source.
The X-rays scatter off the atoms in a crystal.
Those X-rays fly onto either a piece of film, or a digital X-ray detector plate.
Either way, we end up with a beautiful array of dots called a diffraction pattern.
This pattern is beautiful – but doesn’t seem to look like anything?
Ah, but there’s a relationship between the placement of the atoms, and where the X-rays deflect off of them – just like there’s a relationship between a pool ball bouncing off of other pool balls.
Think about it: If you know how a pool table is set up, what balls are made of, and see how the balls move after being it, then you could use math to work backwards.
Just by seeing the results of where the balls are scattering to, you could work backwards to figure out where the balls originally where.
from Banks and Kicks in Pool and Billiards, Dr. Dave Alciatore, Billiards and Pool Principles, Techniques, Resources
The same is true here: We can use math to figure out where each individual atom in the molecule is!
Let’s follow the steps below:
On the left, we see X-rays leave a source. Some of these x-rays hit a lead screen. All those X-rays are stopped.
Only a thin, focused beam of X-rays makes it thru the slit.
Those X-rays hit our crystal sample.
The X-rays bounce off the atoms, like pool balls bouncing off of each other.
(This GIF created by Abhijit Poddar, ‘E-learning’ of select topics in solid state physics and quantum mechanics)
Some of the x-rays bounce onto a film plate. This makes an image.
We end up with a diffraction pattern on film.
Figure 11.4, Purves’s Life: The Science of Biology, 7th Edition
Once we have a diffraction pattern, we use math to work backwards:
We figure out where the atoms must have been.
The result is an electron density map.
This traces out the shape of the atoms in the molecule.
Left image: X-ray diffraction pattern, Wikimedia. Right upper image: electron density map. Right lower image: model fitting atoms to the density map.
Appearance of a zone of the electron density map of a protein crystal, before it is interpreted
The same electron density map after its interpretation in terms of a peptidic fragment.
These last two images come from CSIC Crystallography
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External resources
Welcome to the world of Crystallography: The Spanish National Research Council
Cryo Electron Microscopy
Cryo-EM is an electron microscopy (EM) technique applied on samples cooled to cryogenic temperatures and embedded in an environment of vitreous water.
An aqueous sample solution is applied to a grid-mesh and plunge-frozen in liquid ethane or a mixture of liquid ethane and propane.
While development of the technique began in the 1970s, recent advances in detector technology and software algorithms have allowed for the determination of biomolecular structures at near-atomic resolution.
This has attracted wide attention to the approach as an alternative to X-ray crystallography or NMR spectroscopy for macromolecular structure determination without the need for crystallization.
Cryo-electron microscopy wins chemistry Nobel, Nature
KaiserScience 