For instance, when chlorine accepts an electron from sodium, the sodium ion that is formed will have one more proton than electrons. It will therefore have a positive charge and be called a cation . It will take on a negative charge and be called an anion . The compound formed by this transfer of electrons is sodium chloride or table salt, which is nothing like the highly reactive sodium or extremely poisonous chlorine from which it was formed. Until now we have focused on the nucleus.
Lets turn our attention to the electrons, which surround the nucleus of the atom.
Electrons are located in energy levels a term which has replaced the word shells , which was once used to describe the location of electrons. The word shell suggests a fixed position, which is far from reality. We will use energy level to describe the possible location of electrons. There are seven energy levels. Each has a specific maximum number of electrons that can exist in it.