How can sodium and chlorine ,form salt?

Sugar and wood are both made from carbon, hydrogen and oxygen. They are compounds, made of molecules, and their ingredients are elements, made of atoms. A molecule of assorted atoms forms a vastly different substance from its basic ingredients. There are only about 100 different elements, but their atoms combine to form the millions of different substances in the world around us.

This bit of laboratory magic seems to call for wand and cloak. The chemist takes a jar filled with yellow green chlorine gas, this element active enough to set water on fire. In a few minutes, white crystals form in the jar. Several quintillion atoms of chlorine and sodium have combined to form molecules of sodium chloride   the chemical compound we call table salt.

Actually, this is not magic. It is the kind of chemical activity going on all the time between the atoms from which our world is made. Elements are made of atoms and atoms combine to form molecules. Compounds are made of molecules and they are very different from the element ingredients from which they are made. The compound liquid water, for example, is made from the two gaseous elements hydrogen and oxygen.

Compounds are formed and reformed by the electron particles which swarm outside the core or nucleus of the atom. Each electron is a charge of negative electricity and a normal atom has an equal number of electrons and protons. The protons are locked 3n the nucleus and each is a charge of positive electricity. An atom with equal positive and negative charges is electrically neutral.

But some atoms are more eager to form molecules with other atoms.

This is because electrons are arranged in shells, two in the inner shell, eight in the second and third shells. An atom, it seems, likes to have its electron shells completed; The sodium atom has but one electron in its third shell. The chlorine atom needs one electron to complete itsthird shell.

The lone outer electron of a sodium atom hops over to complete the outer shell of a chlorine atom   but this upsets the electrical balance of both atoms: The sodium atom loses a negative charge and the chlorine atom gains one. The problem is solved by a partnership. The two atoms combine to form a balanced molecule of sodium chloride.

The salt molecules cling to each other and stack themselves up in a lattice of neat cubes. Gradually they build a grain of salt. The number of molecules in a grain of salt can be written as ten, followed by 24 zeros. This magic of making compounds from elements is on a scale far too small for our eyes to see: Many tricks of atoms and molecules have been solved by our patient and clever chemists, but the magic of chemistry never ends.