# What is Stuff Made of?

I expect you've often wondered what would happen if you were to cut something in half, then cut one of the halves in half again, and keep on doing the same thing over and over again, making smaller and smaller pieces each time? Could you keep doing this forever, or would there come a time where the tiny piece you're trying to cut in half is so small that it simply can't be split any further?
There does in fact come a point where things can't be chopped up into smaller pieces, and this happens when we get down to the level of atoms (though they can still be broken into even smaller bits by smashing them together at extremely high speeds, but we'll get to that later). If you start with a piece of string, cut it in the middle and throw one half away, it would only take ten such cuts to make a string a thousand times shorter than the original: the first cut gives you a piece of string half as long as the original length; the second cut gives you a piece four times shorter than the original length, the third cut gives you a piece eight times shorter than the original length, the fourth cut gives you a piece of string sixteen times shorter than the original length, the fifth cut makes it thirty two times shorter, the sixth cut makes it 64 times shorter, the seventh cut makes it 128 times shorter, the eighth cut makes it 256 times shorter, the ninth cut makes it 512 times shorter, and the tenth cut gives you a piece of string 1024 times shorter than the original piece of string.
As you can see, every ten cuts makes the piece of string about a thousand times shorter, so by the time you have made just 20 cuts, the piece of string will be a million times shorter than its original length. If the original piece of string was about half the length of a pencil, you will still have to make yet another ten cuts before you have a piece of string just a single atom long. So, it turns out that you only need to make thirty cuts to get to the point where you can't cut the string any shorter, but at this point the piece of string is a thousand million times shorter than its original length. So, a thousand million (that's a billion) atoms lined up in a row would only extend to the length of a short pencil - you should now be able to see that atoms are very small indeed.
When scientists discovered atoms, they hoped they had found the smallest pieces of matter that exist, but it soon became clear that atoms could be split into smaller parts too, though they had to be smashed together at very high speeds to break them apart completely. The smaller pieces found in the atom are called protons, electrons and neutrons. There are over a hundred different kinds of atoms and they behave differently depending on how many protons they have inside them.
See how many of these atoms you have heard of: hydrogen atoms have just a single proton, helium atoms have two protons, lithium atoms have three, beryllium atoms have four, boron atoms have five, carbon atoms have six, nitrogen atoms have seven, oxygen atoms have eight, fluorine atoms have nine, and neon atoms have ten protons. Atoms normally have the same number of electrons as protons, so you would expect an oxygen atom with eight protons to have eight electrons as well, but the number of electrons can actually vary, so it is always the number of protons that decides what kind of atom an atom is: an atom which has eight protons and only seven electrons is still an oxygen atom, while an atom which has eight electrons and only seven protons must be a nitrogen atom. If you want to take a little look ahead, click here to see all the different kinds of atoms listed in a table - you can run the cursor over them to see their vital statistics, and if you want to look further ahead you can click on them to learn about some of the chemical reactions they are involved in (though there isn't a lot of information there yet as it's still being written).
Protons and electrons are strongly attracted to each other, so they tend to pair up with each other, rather like people getting married. Protons always try to push other protons away, and electrons always try to push other electrons away, but an electron and a proton are always attracted towards each other, so an atom with eight protons will automatically try to collect eight electrons to match. The forces used by protons and electrons to pull or push each other about are the same forces that make magnets work, so you can feel their strength directly for yourself just by holding a couple of magnets near each other. Normally the protons and electrons in a material are jumbled about in such a way that all the forces cancel each other out and the material doesn't feel magnetic at all, but a magnet has its protons and electrons lined up in such a way that the forces don't entirely cancel out until you are much further away: one end of the magnet will seem to push and pull like a giant proton, while the other end will seem to pull and push like a giant electron. Many fridge magnets seem to break the normal rules because they don't have the usual two ends or sides with opposite forces that you might expect from magnets, but this is because they use a clever trick called a "Halbach Array", and if you're keen you can research that for yourself by searching for the term on Wikipedia.
You might also be surprised to learn that all materials push and pull at each other every bit as strongly as magnets, but the pushing forces are completely cancelled out by the pulling forces in every direction, so you don't notice any forces between them at all. Most of the pushing and pulling forces in magnets also cancel each other out, so it is only a tiny proportion of the forces that you are able to feel when you play with magnets. You can get a better idea of how strong these forces really are when you realise that they are the same forces that bind atoms to other atoms: if you try to break a piece of wire by pulling the two ends in opposite directions, it's the magnetic forces holding all the atoms to each other that prevent it from breaking, and that shows the true strength of magnets.
In addition to electrons and protons, atoms have neutrons, but neutrons are less exciting because they don't seem to do much other than make atoms heavier, though they do actually have a very important job to do because they are needed to hold protons together in clumps at the centre of atoms: protons normaly try to push each other apart, but neutrons are somehow able to lock them together. Most of the lighter atoms have as many neutrons as protons, but heavy atoms usually have many more neutrons than protons because they need a lot of extra neutrons to lock their many protons together. The lightest atom of all, hydrogen, usually has no neutrons in it at all: it only has the one proton and so there is no other proton in the atom to lock it to (although some hydrogen atoms do contain one or two neutrons which do nothing more than add weight. Neutrons are called neutrons because they are neutral: they don't push or pull anything around, or at least, not on the outside, but on the inside it may be a different story because a neutron is really just a special kind of proton with its own electron built into it.
Neutrons and protons sit together in a clump called the nucleus which is found in the middle of their atom, while the rest of the atom is made up of "empty" space through which the electrons zip around at high speed. The weight of an atom is simply a count of the number of protons and neutrons inside its nucleus: they both weigh more or less the same (the neutron is a fraction heavier), while electrons weigh about a thousand times less: if you add the weight of an electron to a proton, you then have the weight of a neutron, but this is unimportant when it comes to the relative weights of atoms: all you need to know is that electrons weigh next to nothing (but not quite nothing), while protons and neutrons are comparitively heavy and weigh much the same as each other. Heavy materials like lead are heavy because each lead atom has huge numbers of protons and neutrons inside it (82 protons and on on average 125 neutrons), whereas lightweight atoms like helium have very few protons and neutrons in them: just two of each, though that makes it four times heavier than the only lighter atom, hydrogen.
Hydrogen and helium are the lightest two elements, and both are lighter than air, as you can see when balloons filled with these gases go up rather than down if you let go of them, but they still have some weight: if there was no air to get in the way they would actually fall down to the ground instead of going upwards, because when a balloon goes up is is actually being pushed upwards by heavier air shoving its way in underneath. The same thing happens with air in water: it is pushed up by the water trying to get under it, but once the air reaches the surface it immediately stops going upwards and just sits on top of the water, pressing down on it with its much lesser weight. If you take all the water away, the air will fall back down again into the space left behind. By the way, while helium atoms are four times as heavy as hydrogen atoms, helium gas is only twice as heavy as hydrogen gas: this is because each helium atom floats around on its own, but hydrogen atoms attach themselves together in pairs, forming what we call hydrogen molecules: this means that each individual piece of hydrogen gas is made of two atoms, while each piece of helium gas is made of just one atom.
While the protons and neutrons sit in a tight clump (the nucleus) in the middle of an atom, the electrons buzz round them further out, filling the space around the nucleus rather like a ghostly cloud. Electrons are used to tie atoms together magnetically, and these electrons are then shared between the atoms which they tie together. Carbon atoms like to share four of their six electrons with other atoms, just so long as those other atoms are prepared to share the same number of their electrons in return. There are only a few other atoms which like to share four of their electrons with other atoms in this way, so carbon is unusually good at joining up with other atoms to make long chains (as in wood) or forming solid blocks (diamonds are made entirely out of carbon atoms). Some atoms don't like to share any of their electrons with other atoms: helium (which has two protons) and Neon (which has ten) never like to share any of their electrons, so they are extremely reluctant ever to attach themselves to other atoms. You will learn a lot more about this when you study chemistry.