There are very tiny parts in all substances. These parts are called atoms. We can't see them because they are to small. There are many diferent kinds of atoms, but they are all built in the same way.
All atoms have a nucleus. The nucleus is known as the centre of the atoms. In the nucleus there are protons and neutrons. Around the nucleus there a clouds of particles. These particles are called electrons. The electrons move around the central nucleus.
The nucleus of an atoms carries positive electric charges. and each electrons carries negative electric charges. Electrons are very small and very light in weight. Every small piece of substance has a lot of electrons.
Different kinds of atom have different sizes of nucleus and different numbers of electrons. There is only one electron in the hydrogen atom. There are seven electrons in the nitrogen atoms and eight in the oxygen atoms. An atom of iron contains twenty six electrons.