A world of atoms. The atom up close.

1. Inside atoms and elements

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Democritus ripping up paper - interactive graphic

Picture 1.4. The Greek philosopher, Democritus thought about what the smallest piece of matter might be.

	The atom up close

		For over 2000 years, people have been wondering what the fundamental building blocks of matter might be. In about 400BC), the Greek philosopher, Democritus, considered what would happen if you kept ripping up a piece of paper. He reasoned that the paper (and everything else) must be made of tiny, indivisible blocks. He called these blocks atom (which means uncuttable). These blocks would be fundamental. That means they don't change, they last for ever and they cannot be broken down any further. The matter around us (including the paper) changes because the atoms get arrqanged differently. However, the atoms themselves would never change. We have a slightly different picture of atoms.

	How big is our atom?

		An atom is tiny - about a tenth of a millionth of a millimetre across (0.0000001 mm). You might think that there could be nothing smaller than an atom and that it is a fundamental particle. However, this is not the case. Atoms have structure - they are made up of even smaller, simpler particles.

Picture 1.5 The atom has a nucleus with electrons outside it. This picture is useful but doesn't take account of the fact that the nucleus is so much smaller than the atom - like a pinhead in the middle of an athletics stadium.

	What's inside an atom?

		An atom contains electrons. We know this because we can knock them off, forming ions. The electrons are whizzing around in a cloud outside a central nucleus. The nucleus is much smaller than the atom (its diameter is about 100,000 times smaller than the atom's diameter). This is like a pinhead in the middle of an athletics stadium: the pinhead is the nucleus; the spectators are like the electrons (if they were running about, that is).

	Is that it?

		So are the electron and the nucleus fundamental particles? Yes and no. The electron is fundamental - it cannot be split any further. However, the nucleus is made of even smaller particles.