On Earth, we can see and touch millions of different kinds of objects.

In our history, humans have tried to understand how these millions of different kinds of things could exist.

One explanation is that they could all be made from a much smaller number of basic building materials.

The ancient Greeks thought that everything is constructed from four elements

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• Earth
• Air
• Fire
• Water

We see evidence of this in the air entering and leaving our bodies, our heat (fire), our solid flesh and bones (earth), and our water parts (blood, sweat, tears).

Greek Idea of an Element

Everything is made of elements. If we take anything and can break it down, we will find it is made of one or more of the four elements.

We cannot break any of these four elements into something different.

Instead of four elements, we have discovered that 92 elements naturally occur on our planet.

Scientists discovered that water can be broken down into two simpler building blocks.

Imagine you own a company that has the job of constructing a planet such as Earth.

You would need only 92 different storage containers for your building materials.

Whenever you needed anything like a rock or leaf or tooth, you could just gather the specific elements that make up that object, and put those elements together in exactly the right way.

Most of the things on or in planet Earth are made from just a few elements.

You will need large amounts of a few elements, such as...

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• hydrogen
• oxygen
• carbon
• nitrogen
• iron
• silicon

Those are the ingredients of water, soil, air, and living organisms.

The 92 elements are the parts of the Earth system.

When two or more of these elements combine, they form new whole things that have different properties than the parts.

Imagine all the ways you could combine 92 different things.

No wonder we can have millions of different kinds of things on our planet.

Definition Update

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• Everything is made of elements. If we take anything and can break it down, we will find it is made of one or more of the 92 elements
• We cannot break any of these 92 elements into something different.

What happens when we try to break down an element?

Gold

You can run electricity through gold, it will still behave just like gold.

You can pound it incredibly thin, and it still behaves just like gold.

Shwedagon Pagoda in Myanmar

Thin gold leaf still has the color, brilliance, and strength of gold.

But there is a limit to how small something can be and still be gold.

We call that very smallest piece an atom of gold.

An atom is incredibly small. Try this....

Take a sheet of paper and cut it in half.

Cut the half in half and keep doing this until you can no longer cut the paper in half

To get to the size of an atom, you would have to cut the paper about 20 more times.

"What happens if we cut the atom into pieces?"

It takes an incredibly huge amount of energy, but, yes, atoms can be broken.

When we break an atom of gold, it stops being an atom of gold.

If we could break it up into all its pieces and then separate those pieces, we would have different pieces that we call subatomic particles.

"Subatomic" means smaller than an atom, and "particle" is another word for pieces.

Updated definition

Changes: now include atoms, and that we can break an atom into pieces so small that it no longer that element.

Everything is made of elements. If we take anything and break it down, we will find it is made of one or more of the 92 elements.

Any piece of an element is made up of atoms of that element. Each of those atoms is essentially the same as every other atom of that element.

We can break an atom of an element into subatomic particles. When we do that, it is NO LONGER that element.

Atoms Are Systems

The three questions

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• What are the parts of the system?
• How does the system work as a whole?
• How is the system itself part of larger systems?

Why are the elements different from each other?

It probably has something to do with the atoms.

But what makes one atom different from another atom? Why is one atom hydrogen, while another atom is oxygen or gold?

Question #1: What are the parts of the atom?

Atoms can be broken into subatomic particles.

We need to know about the three main ones: protons, electrons, and neutrons

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Everything is made of elements. If we take anything and can break it down, we will find it is made of one or more of the 92 elements.

Any piece of an element is made up of atoms of that element. Each of those atoms has the same number of protons.
If we change the number of protons, we change an atom from being one element into being a different element.

Many people have wanted to change lead into gold

They could never succeed because they did not know what you know about elements and subatomic particles.

None of the methods they tried had any chance of changing the insides of atoms.

How does the atom work as a whole?

By the year 1900, scientists knew that atoms had positive and negative electrical charges.

In 1908, a scientist from New Zealand named Ernest Rutherford decided to test that idea by shooting high-speed, positively charged particles at a thin sheet of gold foil.

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Rutherford had two questions in mind: 1) What will happen when positively charged particles get shot at a thin sheet of gold foil? 2) What will this experiment tell us about the insides of atoms?

However, Rutherford surprised himself and the rest of the scientific community when he discovered that some of his high-speed bullets came bouncing back at him from the gold foil.

He often said that his results surprised him as much as if he had shot a cannon ball at tissue paper, and the cannon ball bounced back at him.

Rutherford had discovered what we call the atomic nucleus, the very tiny central region of the atom that has practically all the atom's mass.

Those subatomic bullets had bounced back at him because they had hit the atomic nucleus

This nucleus occupies a very tiny fraction of the atom's space.

The vast majority of Rutherford's subatomic bullets came nowhere near the nucleus so they passed right through the atom with little change in their path.

The massive protons and neutrons are located in the atom's nucleus. The tiny electrons are found in the outer edges of the atom.

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You may have seen drawings of atoms with electrons traveling in circles around a central nucleus.

However, no drawing can accurately show you what the inside of an atom looks like.

For one thing, it could never fit on a page or whiteboard or computer screen.

We could use a marble to represent the nucleus of an atom.

If we put the marble in the center of the LA Coliseum...

... the electrons would be represented by wisps of dust waving for the home team from the outer edges of the structure.

The vast majority of the atom seems to be empty space.

So matter is pretty weird.

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