ATOMS.

            Single atoms are too small to see, even with microscopes. For example four billon atoms would fit side by side on the full stop at the end of this sentence.

            Every atom consists of a nucleus and a cloud of particles called electrons.

CLICK HERE TO SEE A SODIUM ATOM GREATLY MAGNIFIED

            Every nucleus consists of two sorts of particles, protons and neutrons. These particles are very light. Their mass is measured in atomic mass units and they also have an electric charge.

Particle in an atom   Mass                  Charge

Proton                      1 unit                  Positive charge(+1)

Neutron                    1 unit                  None

Electron                    Almost nothing  Negative charge(-1)

ATOMIC STRUCTURE

            The different levels for the electrons are called electron shells. Each shell can hold a limited number of electrons:

The first shell can hold up to 2 electrons

The second shell can hold up to 8

The third shell can hold up to8

                        BY SINEAD DEVINE 10B/G.