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Let's look at an atom

An atom is a really small particle. An atom is so small that it cannot even be seen with a microscope. So scientists had to make predictions about what they really look like. Scientists like John Dalton came up with theories or ideas about atoms. John Dalton thought that atoms were the smallest particles that could exist. He thought that atoms were small little balls packed together.

Then scientists found that atoms behaved as though they were made up of tiny particles that had a negative or minus charge. (Remember they can't SEE the atoms - they can only look at the way they behave). These particles were smaller than atoms. They called them electrons, protons and neutrons. This is what an artist thinks an electron might look like.

Atoms can't be seen and have never been seen. Scientists use models to help understand ideas that cannot be seen directly. The model of the atom was constantly changing. The next model scientists proposed looked like a ball of chocolate chip dough. The cookie dough is the positive part and the chocolate chips are the electrons.

Atoms were known to be neutral or have no charge. Scientists thought there had to be positive charges in the atoms and negative charges in the electrons. Scientists made a new model of the atom. It had electrons circling around a small central core of protons which they called the nucleus. The number of protons and electrons were equal so that the charges would cancel each other. It looks a bit like a tiny solar system, with the sun at the centre, and planets going around it.

Scientists now have other models, but we'll stick with this one because it is simple to understand. Inside the nucleus of the atom are protons (with a positive charge) and neutrons (with no charge). The electrons outside have a negative charge, remember. So if you add the negatives together, and the positives, they cancel each other out by adding up to zero.

But guess what? There are even smaller pieces moving around in those atoms. Scientists have many names for those pieces, but you may have heard of NUCLEONS and QUARKS. Nuclear chemists and physicists work together with special machines called particle accelerators to learn about these tiny, tiny, tiny pieces of matter.