Up, Up 'n Atom!

In this article we will cover:

1.

• What is an atom?

• What is inside an atom?

• What is charge?

• What is mass?

• How do atoms react with each other?

• Shells and valence

1

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Before we begin, let's think about this picture

At the top of this page, we have a cartoon drawing of an atom. Scientists use images like these to help us visualise things, but they are not necessarily what they actually look like. You could draw a picture of your home town and include your house or apartment, and make it bigger to stand out and show where you live. And you could also draw where your friends live and where you go to school or where you work and make those buildings bigger. Then you could do the same with a hospital, sports stadium, shops you like to go to etc. You might even consider using some simple lines to represent all the other buildings. You'll then end up with a layout of the town, but the buildings aren't to scale and even the exact positions of them relative to each other may not be accurate. Still, it's a good enough representation to suit your purpose. The same goes with this picture.

So back to the atom

Atoms are the building blocks of everything. They are the smallest pieces of something that you'll find.

Atoms make up everything (with few exceptions like heat and light, but don't worry about the exceptions until you have a clear understanding of the basics).

So if you've started with the article on elements first, you were advised to come here. To get to grips with what atoms have to do with elements, think of it this way: elements are the different types of atoms that exist in the universe. In order to understand what they are and how they work, we need to take a look inside one of them:

Helium atom

As we can see in the above picture of a helium atom, an atom is made up of different subatomic particles: protons, neutrons and electrons. The nucleus is in the centre of the atom and contains the protons and neutrons, while electrons orbit the nucleus (zoom around it constantly).

Another thing to know about these subatomic particles is charge. This is what a particle has that allows it to attract (pull) or repel (push away) another particle which also has charge, if they are close enough to each other. A particle can have either a positive (+) or a negative (-) charge. A particle with positive charge will attract a particle with negative charge. But if a particle with positive charge meets another particle with positive charge, the two will repel each other. Two particles with negative charge will likewise repel each other. If they're the same charge, we refer to them as having like charge, while different ones are opposite.

So:

like charges repel

opposite charges attract

Electrons, which orbit the nucleus, are negative.

Protons, which are in the nucleus, are positive.

Neutrons, which are also in the nucleus, are neutral. In other words, they have no charge (as particles don't need to have a charge at all).

The last thing to note, is that protons and neutrons have a lot more mass than electrons.

Mass?

If you compare yourself to a bus, you can say that the bus has more mass than you, which causes it to be heavier. The bus also has more mass than a car, which in turn, has more mass than you (sorry to disappoint you, but you're not that heavy compared to some other stuff out in the world).

Subatomic particles are incredibly small. So small in fact that you can't even see them. But we can still compare their mass with each other, which is important to understand how they work.

It may be easy to think of electrons, which have the least mass of the three subatomic particles, as being the smallest. But it's not actually correct to talk about size. If you had a dustbin bag full of dirty tissues, it may be larger than a brick, but that brick would have more mass than the bag of tissues. A larger size doesn't necessarily make something heavier (I'll explain why that is in a later article). So just stick with saying that one particle has more mass than another one.

So there's the rundown of the atom. You can now go back to the article on elements. After you've read the rest of the elements article, come back here and we'll look at how atoms interact with each other.

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How atoms bind together

An atom can form a bond with another atom of the same or different element. As you might have guessed, it has to do with the charges of their protons and electrons. But before we learn how charges affect bonds, we need to see what electrons do with each other. Since they are on the outside of atoms and have so little mass, they move around a lot and are the most likely to interact with other particles. They are the key players in chemistry, which essentially, is the study of how atoms interact with each other.

Electrons like to pair up. Don't worry for now how two negative particles can do that instead of just pushing each other away. But an electron spinning around the nucleus on its own will want to pair with another electron on its own. They can only form pairs though, as the old saying goes, "three is a crowd".

A molecule of water

When two or more atoms form bonds with each other, by having the electrons of one atom form pairs with the electrons of another atom, we end up with a molecule. If you remember from the article on elements, two hydrogen atoms can combine with one oxygen atom to form water. So let's see what this looks like: (note that protons and neutrons are not shown, instead the whole nucleus is represented by a sphere.)

Hydrogen atoms

Oxygen atom

Two hydrogen atoms plus one oxygen atom = one water molecule or H2O

As you can see, oxygen has two free electrons while hydrogen has one. This is why two hydrogen atoms can form bonds with one oxygen atom. But you can also have oxygen molecules and hydrogen molecules, whereby two atoms of the same element form bonds with each other, like this:

As hydrogen has one free electron, we say that hydrogen has a valence of one. Oxygen, which has two free electrons, has a valence of two. Knowing the valence of an element is important to understand how the atoms of different elements will form bonds with other atoms. There are even elements with no valence at all (such as helium, shown near the beginning of this article), which as you can guess, will mean they don't react with anything else.

Shells

The article on elements revealed that each element has a certain number of electrons and protons, which is known as the atomic number. Hydrogen only has one electron and one proton. We'll leave protons out for now, and focus on electrons. The single electron of hydrogen orbits the nucleus (which is just one proton, by the way) and is left free to form a pair with another electron. The electron occupies the first shell, which is the area closest to the nucleus. The second shell is the area a little further away from the nucleus.

The first shell can hold 2 electrons. In the case of hydrogen, the shell is not full and so the lone free electron can pair with another electron, or in other words, the atom can form a bond with another atom. Helium is the next element in the Periodic Table (as you read from left to right, which follows the elements' atomic numbers) and it has its first shell already full with 2 electrons (hence it can't react with anything).

Now, you can see that when I draw the first shell, it has its electrons on either side of the shell. They are still paired up though, it's just the way we draw the first shell.

All the other shells can hold 8 electrons (and we draw the paired up ones close to each other).

Oxygen has 8 electrons in total. In order to figure out the valence of oxygen, we need to see where the electrons go. The way to do this is to imagine you have a complete oxygen nucleus but its electrons are missing. You then add electrons until you've added all 8. So the first electron goes into the first shell. Then the second electron pairs up with the first and you have the first shell full (see the image below).

Now the thing with electrons is that, although they can pair up, they will only do so if there's nowhere else within a shell for them to go. The first shell can only carry two, so the second electron has to go and pair with the first one. You have to fill up the shells in order, so the next electrons will go into the second shell until that is full. You can fill the second shell with 4 electrons before you have to start pairing them up. We can show them like this:

We have 2 electrons left. You have to start pairing them in the second shell now, so they'll each pair with one of the electrons that are already there. So now we end up with an oxygen atom with all its 8 electrons:

As you can see, that's why oxygen has a valence of 2 and can thus bond with two hydrogen atoms to form water.

So that's the basics of atoms.

Now you can go on to reading the Key Articles to open up the whole wide world of science. I suggest you start with 'Let's Get Physical' and 'Chemical Bonding', which contain important stuff for you to understand science from then on. After that, just surf this site to get what you want out of it. Have fun!