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What are atoms? Let’s start with the ideas of the ancient Greek philosophers:


One ancient idea was that there were four basic elements:

By Ham549 http://ham549.deviantart.com/art/ye-old-periodic-table-297608017



Why would ancient thinkers believe that there were only four elements? Think of what they observed: If you burned a piece of wood, what would you see? Fire being released, also smoke (“air”) and after the burning was done you would have ashes (“earth”).
Water being the opposite of fire would extinguish it, so you could even make rudimentary chemical equations to justify your theory:

Wood (earth/air/fire) —> Earth (ashes) +air (smoke) + fire (flame)

In physics we learn how our universe is made of elements,
and how each of the elements is made of sub-atomic particles.

Online textbook chapters to read

Chap 2 Structure of Matter and the Chemical Elements

Chap 11 Modern Atomic Theory & Periodic table

Atoms Around Us


You are made of different types of atoms.

Atoms are building blocks. If you want to create a language, you’ll need an alphabet.

If you want to build molecules, you will need atoms of different elements.

Elements are the alphabet in the language of molecules. Each element is a little bit different from the rest.

Why are we talking about elements when this is the section on atoms? Atoms are the general term used to describe pieces of matter.

You have billions of billions of atoms in your body. However, you may only find about 40 elements.

You will find billions of hydrogen (H) atoms, billions ofoxygen (O) atoms, and a bunch of others.

All of the atoms are made of the same basic pieces, but they are organized in different ways to make unique elements.

Common Elements

Common elements can build very different molecules.

If you read a book, you will find words on each page.
Letters make up those words.
In English, we only have 26 letters, but we can make thousands of words.
In chemistry we have about 120 elements.
When you combine them, you can make millions of different molecules.

Molecules are groups of atoms bonded together in the same way that words are groups of letters.

An “A” will always be an “A” no matter what word it is in. A sodium (Na) atom will always be a sodium atom no matter what compound it is in.

While the atoms have different masses and organization for each element, they are all built with the same parts. Electrons, protons, and neutrons make the Universe the way it is.

From Simple to Complex

Small parts combine to form larger structures.

If you want to do a little more thinking, imagine the smallest particles of matter.

Super-tiny subatomic particles are used to create the parts of atoms. Protons, neutrons, and electrons can then organize to form atoms.

Atoms are then used to create the molecules around us.

As we just learned, there are almost 120 elements that can be found in the molecules we know. Smaller molecules can work together and build macromolecules. It just goes on. Everything you see or imagine is built from something else.

You could start really small…

– Particles of matter
– Atoms
– Molecules
– Macromolecules
– Cell organelles
– Cells
– Tissues
– Organs
– Systems
– Organisms
– Populations
– Ecosystems
– Biomes
– Planets
– Planetary Systems with Stars
– Galaxies
– The Universe

Atoms Are Building Blocks

Atoms are made of electrons, neutrons, and protons.

Atoms are the foundation of chemistry. They are the basis for everything in the Universe.

As you know, matter is composed of atoms. Solids are made of densely packed atoms while gases have atoms that are spread out.

We’re going to cover basics like atomic structure and bonding between atoms.

As you learn more, you can move to the reactions and biochemistry pages and see how atoms form compounds that help the biological world survive.

Are there pieces of matter that are smaller than atoms? Sure there are.

Super-small particles can be found inside the pieces of atoms. These subatomic particles include nucleons and quarks. Nuclear chemists and physicists work together at particle accelerators to discover the presence of these tiny, tiny, tiny pieces of matter. However, science is based on the atom because it is the smallest distinct unit of matter.

Three Easy Pieces

three basic parts of an atom:

electrons, protons, and neutrons.

Electrons have a negative ( – ) charge.

Electrons are found in orbitals that surround the nucleus of an atom.

Protons and neutrons are found in the nucleus.

Protons have a positive ( + ) charge.

Neutrons are neutral – they have no electrical charge!

Atomic mass,weight,number

Atomic weight = # of protons + # of neutrons

Atomic number = # of protons

So what would this mean?

Helium notation


Every element is unique and has an atomic number. That number tells you the number of protons in every atom of the element. The atomic number is also called the proton number.

How much does an atom weigh?

Mass of proton = 1.672 x 10-27 kilograms

Remember negative exponents? That means that the decimal moves to the left.

So this number really means:

00.000000000000000000000000001672 kilograms

That’s a wicked tiny amount.

As you can see from the pic below, neutrons and protons have almost the same mass.

Mass Protones-neutrones-y-electrones
What about the mass of an electron?

It is “something-something” time 10 to the negative 31 kilograms.

How much larger is a proton, as compared to an electron?

Hard way to find out:
Do long division: 1.672 x 10 -27 kilograms / 9.109 x 10 -31 kg =

Easier way to find out:
Use a calculator to do the division: 1.672 x 10 -27 kilograms / 9.109 x 10 -31 kg =

Easiest way to find out: Estimate, using orders of magnitude:

10 – 27 / 10 -31 = 4 orders of magnitude


atomic mass

What is inertia? What is mass?
How is mass related to weight?

Inertia, mass and weight

Also see:

The Element song Tom Lehrer’s song about the periodic table, The Elements!

They Might Be Giants: Meet The Elements Song
They Might Be Giants: Meet the Elements

ACS Middle School Chemistry Lessons

Learning Standards

2016 Massachusetts Science and Technology/Engineering Standards

8.MS-PS1-1  Develop a model to describe that (a) atoms combine in a multitude of ways to produce pure substances which make up all of the living and nonliving things that we encounter, (b) atoms form molecules and compounds that range in size from two to thousands of atoms, and (c) mixtures are composed of different proportions of pure substances.
• Examples could include drawings, 3D ball and stick structures, and computer representations showing different molecules with different types of atoms.

HS-PS1-7. Use mathematical representations and provide experimental evidence to support the claim that atoms, and therefore mass, are conserved during a chemical reaction…. Mathematical representations include balanced chemical equations that represent the laws of conservation of mass and constant composition (definite proportions), and mass-to-mass stoichiometry.

College Board Standards for College Success

Objective C.1.3 Bonding: Students understand that matter is composed of atoms of elements, most of which are bonded in different but predictable ways.


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