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Avogadro’s law

Previously in Chemistry one has learned about Avogadro’s hypothesis:

Equal volumes of any gas, at the same temperature and pressure, contain the same number of molecules.

Avogardo's Hypothesis gas

Reasoning 

(from Modern Chemistry, Davis, HRW)

In 1811, Avogadro found a way to explain Gay-Lussac’s simple ratios of combining volumes without violating Dalton’s idea of indivisible atoms. He did this by rejecting Dalton’s idea that reactant elements are always in monatomic form when they combine to form products. He reasoned that these molecules could contain more than one atom.

Avogadro also put forth an idea known today as Avogadro’s law: equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

It follows that at the same temperature and pressure, the volume of any given gas varies directly with the number of molecules.

Avogadro’s law also indicates that gas volume is directly proportional to the amount of gas, at a given temperature and pressure.

Note the equation for this relationship.

   V = kn

Here, n is the amount of gas, in moles, and k is a constant.

Avogadro’s reasoning applies to the combining volumes for the reaction of hydrogen and oxygen to form water vapor.

Dalton had guessed that the formula of water was HO, because this formula seemed to be the most likely formula for such a common compound.

But Avogadro’s reasoning established that water must contain twice as many H atoms as O atoms, consistent with the formula H2O.

As shown below, the coefficients in a chemical reaction involving gases indicate the relative numbers of molecules, the relative numbers of moles, and the relative volumes.

Avogadro gas reaction

The simplest hypothetical formula for oxygen indicated 2 oxygen atoms, which turns out to be correct. The simplest possible molecule of water indicated 2 hydrogen atoms and 1 oxygen atom per molecule, which is also correct.

Experiments eventually showed that all elements that are gases near room temperature, except the noble gases, normally exist as diatomic molecules.

As an equation

Avogadro’s Law – also known as Avogadro–Ampère law

when temperature and pressure are held constant:

volume of a gas is directly proportional to the # moles (or # particles) of gas

n1 / V1 = n2 / V2

or

Avogadro's Law gas

What does this imply?

As # of moles of gas increases, the volume of the gas also increases.

As # of moles of gas is decreased, the volume also decreases.

Thus, # of molecules (or atoms) in a specific volume of ideal gas is independent of their size (or molar mass) of the gas.

 

Example problems

These problems are from The Chem Team, Kinetic Molecular Theory and Gas Laws

Example #1: 5.00 L of a gas is known to contain 0.965 mol. If the amount of gas is increased to 1.80 mol, what new volume will result (at an unchanged temperature and pressure)?

Solution:

I’ll use V1n2 = V2n1

(5.00 L) (1.80 mol) = (x) (0.965 mol)

x = 9.33 L (to three sig figs)


Example #2: A cylinder with a movable piston contains 2.00 g of helium, He, at room temperature. More helium was added to the cylinder and the volume was adjusted so that the gas pressure remained the same. How many grams of helium were added to the cylinder if the volume was changed from 2.00 L to 2.70 L? (The temperature was held constant.)

Solution:

1) Convert grams of He to moles:

2.00 g / 4.00 g/mol = 0.500 mol

2) Use Avogadro’s Law:

V1 / n1 = V2 / n2

2.00 L / 0.500 mol = 2.70 L / x

x = 0.675 mol

3) Compute grams of He added:

0.675 mol – 0.500 mol = 0.175 mol

0.175 mol x 4.00 g/mol = 0.7 grams of He added


Example #3: A balloon contains a certain mass of neon gas. The temperature is kept constant, and the same mass of argon gas is added to the balloon. What happens?

(a) The balloon doubles in volume.
(b) The volume of the balloon expands by more than two times.
(c) The volume of the balloon expands by less than two times.
(d) The balloon stays the same size but the pressure increases.
(e) None of the above.

Solution:

We can perform a calculation using Avogadro’s Law:

V1 / n1 = V2 / n2

Let’s assign V1 to be 1 L and V2 will be our unknown.

Let us assign 1 mole for the amount of neon gas and assign it to be n1.

The mass of argon now added is exactly equal to the neon, but argon has a higher gram-atomic weight (molar mass) than neon. Therefore less than 1 mole of Ar will be added. Let us use 1.5 mol for the total moles in the balloon (which will be n2) after the Ar is added. (I picked 1.5 because neon weighs about 20 g/mol and argon weighs about 40 g/mol.)

1 / 1 = x / 1.5

x = 1.5

answer choice (c).


Example #4: A flexible container at an initial volume of 5.120 L contains 8.500 mol of gas. More gas is then added to the container until it reaches a final volume of 18.10 L. Assuming the pressure and temperature of the gas remain constant, calculate the number of moles of gas added to the container.

Solution:

V1 / n1 = V2 / n2

5.120 L 18.10 L
–––––––– = ––––––
8.500 mol x

x = 30.05 mol <— total moles, not the moles added

30.05 – 8.500 = 21.55 mol (to four sig figs)

Notice the specification in the problem to determine moles of gas added. The Avogadro Law calculation gives you the total moles required for that volume, NOT the moles of gas added. That’s why the subtraction is there.

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Charles’s Law

Charles’s Law – also known as Charles and Gay-Lussac’s Law.

Describes how gases tend to expand when heated.

When the pressure on a sample of a dry gas is held constant, the temperature and the volume will be in direct proportion.

Volume proportional to temperature

(Only true when measuring temperature on an absolute scale)

This relationship can be written as:

Charles's law gas

-> Gas expands as the temperature increases

-> Gas contracts as the temperature decreases

This relationship can be written as:

Charles's law gas alternate

Important! This is not a law of physics! Rather, this is a generally useful rule, which is only valid when gas temperature and pressure is low enough for the atoms to usually be far apart from each other.  As we begin to deal with more extreme cases, this rule doesn’t hold up.

Let’s see this in action!

Origin

Named after Jacques Alexandre César Charles (1746 – 1823)  a French inventor, scientist, mathematician, and balloonist. Just so we’re all clear on this, he was kind of a mad scientist. And I say that with the utmost approval!

first balloon flight by Charles and Robert 1783

Contemporary illustration of the first flight by Prof. Jacques Charles with Nicolas-Louis Robert, December 1, 1783. Viewed from the Place de la Concorde to the Tuileries Palace (destroyed in 1871)

 

.Apps

Charles’s law app

Learning standards

Massachusetts Science and Technology/Engineering Curriculum Framework

8.MS-PS1-4. Develop a model that describes and predicts changes in particle motion, relative spatial arrangement, temperature, and state of a pure substance when thermal energy is added or removed.

Next Generation Science Standards

MS-PS1-4. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.

College Board Standards

Objective C.1.5 States of Matter

C-PE.1.5.2 Explain why gases expand to fill a container of any size, while liquids flow and spread out to fill the bottom of a container and solids hold their own shape. Justification includes a discussion of particle motion and the attractions between the particles.

C-PE.1.5.3 Investigate the behavior of gases. Investigation is performed in terms of volume (V ), pressure (P ), temperature (T ) and amount of gas (n) by using the ideal gas law both conceptually and mathematically.

Common Core Math

Analyze proportional relationships and use them to solve real-world and mathematical problems.

Ratios & Proportional Relationships

Ratios & Proportional Relationships

CCSS.MATH.CONTENT.7.RP.A.2

Recognize and represent proportional relationships between quantities.

CCSS.MATH.CONTENT.7.RP.A.2.A

Decide whether two quantities are in a proportional relationship, e.g., by testing for equivalent ratios in a table or graphing on a coordinate plane and observing whether the graph is a straight line through the origin.

CCSS.MATH.CONTENT.7.RP.A.2.B

Identify the constant of proportionality (unit rate) in tables, graphs, equations, diagrams, and verbal descriptions of proportional relationships.

Boyle’s law (gas laws)

A general relationship between pressure and volume: Boyle’s Law

As the pressure on a gas increases, the volume of the gas decreases because the gas particles are forced closer together.

Conversely, as the pressure on a gas decreases, the gas volume increases because the gas particles can now move farther apart.

Example: Weather balloons get larger as they rise through the atmosphere to regions of lower pressure because the volume of the gas has increased; that is, the atmospheric gas exerts less pressure on the surface of the balloon, so the interior gas expands until the internal and external pressures are equal.

from Libretexts, Chemistry, 5.3: The Simple Gas Laws: Boyle’s Law, Charles’s Law and Avogadro’s Law, CC BY-NC-SA 3.0.

This means that, at constant temperature, the pressure (P) of a gas is inversely proportional to the volume (V).

PV = c

Important! This is not a law of physics! Rather, this is a generally useful rule, which is only valid when gas temperature and pressure is low enough for the atoms to usually be far apart from each other.  As we begin to deal with more extreme cases, this rule doesn’t hold up.

Let’s see the relationship in action, here:

Boyle's law pressure temp

from http://www.grc.nasa.gov/WWW/K-12/airplane/boyle.html

How was this general rule discovered?

Early scientists explored the relationships among the pressure of a gas (P) and its temperature (T), volume (V), and amount (n) by holding two of the four variables constant (amount and temperature, for example), varying a third (such as pressure), and measuring the effect of the change on the fourth (in this case, volume).

The history of their discoveries provides several excellent examples of the scientific method.

The Irish chemist Robert Boyle (1627–1691) carried out some of the earliest experiments that determined the quantitative relationship between the pressure and the volume of a gas. Boyle used a J-shaped tube partially filled with mercury.

In these experiments, a small amount of a gas or air is trapped above the mercury column, and its volume is measured at atmospheric pressure and constant temperature. More mercury is then poured into the open arm to increase the pressure on the gas sample.

The pressure on the gas is atmospheric pressure plus the difference in the heights of the mercury columns, and the resulting volume is measured. This process is repeated until either there is no more room in the open arm or the volume of the gas is too small to be measured accurately.

Boyle's Law pressure temp of a gas

Details: Boyle’s Experiment Using a J-Shaped Tube to Determine the Relationship between Gas Pressure and Volume.

(a) Initially the gas is at a pressure of 1 atm = 760 mmHg (the mercury is at the same height in both the arm containing the sample and the arm open to the atmosphere); its volume is V.

(b) If enough mercury is added to the right side to give a difference in height of 760 mmHg between the two arms, the pressure of the gas is 760 mmHg (atmospheric pressure) + 760 mmHg = 1520 mmHg and the volume is V/2.

(c) If an additional 760 mmHg is added to the column on the right, the total pressure on the gas increases to 2280 mmHg, and the volume of the gas decreases to V/3

(This section from from Libretexts, Chemistry, 5.3: The Simple Gas Laws: Boyle’s Law, Charles’s Law and Avogadro’s Law, CC BY-NC-SA 3.0)

 

Learning standards

Massachusetts Science and Technology/Engineering Curriculum Framework

8.MS-PS1-4. Develop a model that describes and predicts changes in particle motion, relative spatial arrangement, temperature, and state of a pure substance when thermal energy is added or removed.

Next Generation Science Standards

MS-PS1-4. Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.

College Board Standards

Objective C.1.5 States of Matter

C-PE.1.5.2 Explain why gases expand to fill a container of any size, while liquids flow and spread out to fill the bottom of a container and solids hold their own shape. Justification includes a discussion of particle motion and the attractions between the particles.

C-PE.1.5.3 Investigate the behavior of gases. Investigation is performed in terms of volume (V ), pressure (P ), temperature (T ) and amount of gas (n) by using the ideal gas law both conceptually and mathematically.

Common Core Math

Analyze proportional relationships and use them to solve real-world and mathematical problems.

Ratios & Proportional Relationships

Ratios & Proportional Relationships

CCSS.MATH.CONTENT.7.RP.A.2

Recognize and represent proportional relationships between quantities.

CCSS.MATH.CONTENT.7.RP.A.2.A

Decide whether two quantities are in a proportional relationship, e.g., by testing for equivalent ratios in a table or graphing on a coordinate plane and observing whether the graph is a straight line through the origin.

CCSS.MATH.CONTENT.7.RP.A.2.B

Identify the constant of proportionality (unit rate) in tables, graphs, equations, diagrams, and verbal descriptions of proportional relationships.

 

Oils

“Oil” is a general name for any kind of molecule which is

nonpolar

that just means that its electrons are evenly distributed

PHET Polar molecules app

liquid at room temperature

of course, it could become solid if cooled, or evaporate if heated

Molecule has one end which is hydrophobic and another end which is lipophilic

The hydrophobic end likes to stick to water molecules. But hates sticking to oils.

The lipophilic end likes to stick to oil molecules, but hates sticking to water,

hydrophobic hydrophilic

Made with many C and H atoms

Oils are usually flammable. Here we see oils in an orange skin interacting with a candle.

flammable orange oil

So Petroleum is?

Petroleum is a mix of naturally forming oils, which we drill from the Earth, and use in a variety of ways. See our article on petroleum and producing power.

Rotary catalytic mechanism of mitochondrial ATP synthase

Introduction

(Text in this section adapted from “ATP synthase.” Wikipedia, The Free Encyclopedia. 27 Mar. 2019.)

ATP synthase is an enzyme that creates the energy storage molecule adenosine triphosphate (ATP).

ATP is the most commonly used “energy currency” of cells for all organisms. It is formed from adenosine diphosphate (ADP) and inorganic phosphate (Pi).

The overall reaction catalyzed by ATP synthase is:

  • ADP + Pi + H+out ⇌ ATP + H2O + H+in

The formation of ATP from ADP and Pi is energetically unfavorable and would normally proceed in the reverse direction.

In order to drive this reaction forward, ATP synthase couples ATP synthesis during cellular respiration to an electrochemical gradient created by the difference in proton (H+) concentration across the mitochondrial membrane in eukaryotes or the plasma membrane in bacteria.

Molecular animation of ATP synthase

Here is a three dimensional animation of all the proteins working together in this complex. We see it situated in a lipid bilayer (organelle membrane.)

GIF mitochondrial ATP synthase

Here is another animation of a similar complex.

GIF mitochondrial ATP synthase 2

Video

Rotary catalytic mechanism of mitochondrial ATP synthase

Learning Standards

(TBA)

Biology, Chemistry, Simple machines

Elements necessary for life

Major elements – CHONSP

Carbon – Used as the major building unit of all organic molecules.

Hydrogen – major component of water. Major component of all organic molecules.

Oxygen – major component of water. Must be transported by our red blood cells.

Nitrogen – needed in all amino acids and proteins. Needed in chlorophyll, which is necessary for photosynthesis.

Sulphur – Used in in fats, body fluids, skeletal minerals, and most proteins.

Phosphorus – Necessary to make DNA and RNA. Also a component of bones and teeth.

periodoc table elements for life biological

Microbial Genomics and the Periodic Table, Lawrence P. Wackett, Anthony G. Dodge and Lynda B. M. Ellis

.

periodic table elements life biological

Microbial Genomics and the Periodic Table, Lawrence P. Wackett, Anthony G. Dodge and Lynda B. M. Ellis

 

There are many essential trace elements in humans

Arsenic – “Despite its poisonous reputation, may be a necessary ultratrace element for humans. It is a necessary ultratrace element for red algae, chickens, rats, goats, and pigs. A deficiency results in inhibited growth (*)

Boron – essential for cell membrane characteristics and transmembrane signaling

Calcium ions are essential for muscle contractions and the clotting of blood. Necessary for cell walls, and bones.

Chlorine – Digestive juices in the stomach contain hydrochloric acid.

Chromium – essential trace element that potentiates insulin action and thus influences carbohydrate, lipid and protein metabolism.

“Chromium is an essential trace element and has a role in glucose metabolism. It seems to have an effect in the action of insulin. In anything other than trace amounts, chromium compounds should be regarded as highly toxic.” (*)

“Cobalt salts in small amounts are essential to many life forms, including humans. It is at the core of a vitamin called vitamin-B12. “ (*)

“Copper is essential for all life, but only in small quantities. It is the key component of redox enzymes and of haemocyanin.” (*)

Fluorine forms a salt with calcium. This salt makes the teeth and bones stronger.

“Iodine is an essential component of the human diet and in fact appears to be the heaviest required element in the diet. Iodine compounds are useful in medicine.” (*)

Iron – used in the hemoglobin molecules, allows your blood to hold oxygen. Iron is only about 0.004 percent of your body mass,

Magneisum “Chlorophylls (responsible for the green colour of plants) are based upon magnesium. Magnesium is required for the proper working of some enzymes.” (*)

Manganese – essential for the action of some enzymes

“Molybdenum is a necessary element, apparently for all species. … plays a role in nitrogen fixation, enzymes, and nitrate reduction enzymes.” (*)

Nickel is an essential trace element for many species. Unknown if so in humans.

“Potassium salts are essential for both animals and plants. The potassium cation (K+) is the major cation in intracellular (inside cells) fluids (sodium is the main extracellular cation). It is essential for nerve and heart function.” (*)

Selenium – essential component of one of the antioxidant defense systems of the body
“essential to mammals and higher plants, but only in small amounts…. may help protest against free radical oxidants and against some heavy metals.” (*)

Silicium – probably essential for healthy connective tissue and bone

Sodium (Na+) and potassium (K+) ions – transmission of nerve impulses between your brain and all parts of the body.

Tin – expected to have a function in the tertiary structure of proteins

Tungsten is needed in very tiny amounts in some enzymes (oxidoreductases)

Vanadium – possible role as an enzyme cofactor and in hormone, glucose, lipid, bone and tooth metabolism.

“Zinc is the key component of many enzymes. The protein hormone insulin contains zinc.” (*)

(*) WebElements: THE periodic table on the WWW
https://www.webelements.com/arsenic/biology.html

Basic chemistry rules are actually magic number approximations

The basic rules of chemistry are magic number approximations

What is Lewis Theory?

This lesson is from from Mark R. Leach, meta-synthesis.com, Lewis_theory

Lewis theory is the study of the patterns that atoms display when they bond and react with each other.

The Lewis approach is to look at many chemical systems, study patterns, count the electrons in the patterns. After that, we devise simple rules to explain what is happening.

Lewis theory makes no attempt to explain how or why these empirically derived numbers of electrons – these magic numbers – arise.

Although, it is striking that the magic numbers are generally (but not exclusively) positive integers of even parity: 0, 2, 4, 6, 8

For example:

  • Atoms and atomic ions show particular stability when they have a full outer or valence shell of electrons and are isoelectronic with He, Ne, Ar, Kr & Xe: Magic numbers 2, 10, 18, 36, 54.

  • Atoms have a shell electronic structure: Magic numbers 2, 8, 8, 18, 18.

  • Sodium metal reacts to give the sodium ion, Na+, a species that has a full octet of electrons in its valence shell. Magic number 8.

  • A covalent bond consist of a shared pair electrons: Magic number 2.

  • Atoms have valency, the number of chemical bonds formed by an element, which is the number of electrons in the valence shell divided by 2: Magic numbers 0 to 8.

  • Ammonia, H3N:, has a lone pair of electrons in its valence shell: Magic number 2.

  • Ethene, H2C=CH2, has a double covalent bond: Magic numbers (2 + 2)/2 = 2.

  • Nitrogen, N2, N≡N, has a triple covalent bond: Magic numbers (2 + 2 + 2)/2 = 3.

  • The methyl radical, H3C•, has a single unpaired electron in its valence shell: Magic number 1.

  • Lewis bases (proton abstractors & nucleophiles) react via an electron pair: Magic number 2.

  • Electrophiles, Lewis acids, accept a a pair of electron in order to fill their octet: Magic numbers 2 + 6 = 8.

  • Oxidation involves loss of electrons, reduction involves gain of electrons. Every redox reaction involves concurrent oxidation and reduction: Magic number 0 (overall).

  • Curly arrows represent the movement of an electron pair: Magic number 2.

  • Ammonia, NH3, and phosphine, PH3, are isoelectronic in that they have the same Lewis structure. Both have three covalent bonds and a lone pair of electrons: Magic numbers 2 & 8.

  • Aromaticity in benzene is associated with the species having 4n+2 π-electrons. Magic number 6.Naphthalene is also aromatic: Magic number 10.

  • Etc.

Lewis theory is numerology.

Lewis theory is electron accountancy: look for the patterns and count the electrons.

Lewis theory is also highly eclectic in that it greedily begs/borrows/steals/assimilates numbers from deeper, predictive theories and incorporates them into itself, as we shall see.


 Ernest Rutherford famously said
“Physics is the only real science. The rest are just stamp collecting”

Imagine an alien culture trying to understand planet Earth using only a large collection of postage stamps. The aliens would see all sorts of patterns and would be able to deduce the existence of: countries, national currencies, pricing strategies, differential exchange rates, inflation, the existence of heads of state, what stamps are used for, etc., and – importantly – they would be able to make predictions about missing stamps.

But the aliens would be able to infer little about the biology of life on our planet by only studying stamps, although there would be hints in the data: various creatures & plants, males & females, etc.

So it is with atoms, ions, molecules, molecular ions, materials, etc. As chemists we see many patterns in chemical structure and reactivity, and we try to draw conclusions and make predictions using these patterns:

This is Lewis theory. But this Lewis approach is not complete and it only gives hints about the underlying quantum mechanics, a world observed through spectroscopy and mathematics.

Patterns

Consider the pattern shown in Diagram-1:

dot pattern 1

Now expand the view slightly and look at Diagram-2

Dot pattern 2

You may feel that the right hand side “does not fit the pattern” of Diagram-1 and so is an anomaly.

So, is it an anomaly?

Zoom out a bit and look at the pattern in Diagram-3, the anomaly disappears

Dot pattern 3

But then look at Diagram-4. The purple patch on the upper right hand side does not seem to fit the pattern and so it may represent anomaly

Dot pattern 4

But zooming right out to Diagram-5 we see that everything is part of a larger regular pattern.

Digital flowers 5a

Image from dryicons.com, digital-flowers-pattern

When viewing the larger scale the overall pattern emerges and everything becomes clear. Of course, the Digital Flowers pattern is trivial, whereas the interactions of electrons and positive nuclei are astonishingly subtle.

This situation is exactly like learning about chemical structure and reactivity using Lewis theory. First we learn about the ‘Lewis octet’, and we come to believe that the pattern of chemistry can be explained in terms of the very useful Lewis octet model.

Then we encounter phosphorous pentachloride, PCl5, and discover that it has 10 electrons in its valence shell. Is PCl5 an anomaly? No! The fact is that the pattern generated through the Lewis octet model is just too simple.

As we zoom out and look at more chemical structure and reactivity examples we see that the pattern is more complicated that indicated by the Lewis octet magic number 8.

Our problem is that although the patterns of electrons in chemical systems are in principle predictable, new patterns always come as a surprise when they are first discovered:

  • The periodicity of the chemical elements

  • The 4n + 2 rule of aromaticity

  • The observation that sulfur exists in S8 rings

  • The discovery of neodymium magnets in the 1990s

  • The serendipitous discovery of how to make the fullerene C60 in large amounts

While these observations can be explained after the fact, they were not predicted beforehand. We do not have the mathematical tools to do predict the nature of the quantum patterns with absolute precision.

The chemist’s approach to understanding structure and reactivity is to count the electrons and take note of the patterns. This is Lewis theory.

As chemists we attempt to ‘explain’ many of these patterns in terms of electron accountancy and magic numbers.


Caught In The Act: Theoretical Theft & Magic Number Creation

The crucial time for our understand chemical structure & bonding occurred in the busy chemistry laboratories at UC Berkeley under the leadership of G. N. Lewis in the early years of the 20th century.

Lewis and colleagues were actively debating the new ideas about atomic structure, particularly the Rutherford & Bohr atoms and postulated how they might give rise to models of chemical structure, bonding & reactivity.

Indeed, the Lewis model uses ideas directly from the Bohr atom. The Rutherford atom shows electrons whizzing about the nucleus, but to the trained eye, there is no structure to the whizzing. Introduced by Niels Bohr in 1913, the Bohr model is a quantum physics modification of the Rutherford model and is sometimes referred to the Rutherford–Bohr model. (Bohr was Rutherford’s student at the time.) The model’s key success lay in explaining (correlating with) the Rydberg formula for the spectral emission lines of atomic hydrogen.

[Greatly simplifying both the history & the science:]
In 1916 atomic theory forked or bifurcated into physics and chemistry streams:

  • The physics fork was initiated and developed by Bohr, Pauli, Sommerfield and others. Research involved studying atomic spectroscopy and this lead to the discovery of the four quantum numbers – principal, azimuthal, magnetic & spin – and their selection rules. More advanced models of chemical structure, bonding & reactivity are based upon the Schrödinger equation in which the electron is treated as a resonant standing wave. This has developed into molecular orbital theory and the discipline ofcomputational chemistry

  • Note: quantum numbers and their selection rules are not ‘magic’ numbers. The quantum numbers represent deep symmetries that are entirely self consistent across all quantum mechanics.

  • The chemistry fork started when Lewis published his first ideas about the patterns he saw in chemical bonding and reactivity in 1916, and later in a more advanced form in 1923. Lewis realised that electrons could be counted and that there were patterns associated with structure, bonding and reactivity behaviour.These early ideas have been extensively developed and are now taught to chemistry students the world over. This is Lewis theory.

_____________________________________________________

Lewis Theory and Quantum Mechanics

Quantum mechanics and Lewis theory are both concerned with patterns. However, quantum mechanics actively causes the patterns whereas Lewis theory is passive and it only reports on patterns that are observed through experiment.

We observe patterns of structure & reactivity behaviour through experiment.

Lewis theory looks down on the empirical evidence, identifies patterns in behaviour and classifies the patterns in terms of electron accountancy& magic numbers. Lewis theory gives no explanation for the patterns.

In large part, chemistry is about the behaviour of electrons and electrons are quantum mechanical entities. Quantum mechanics causes chemistry to be the way it is. The quantum mechanical patterns are can be:

  • Observed using spectroscopy.
  • Echoes of the underlying quantum mechanics can be seen in the chemical structure & reactivity behaviour patterns.
  • The patterns can be calculated, although the mathematics is not trivial.

.