|Hi Kelly, |
An atom is made up of a tiny nucleus surrounded by electrons. The nucleus has a positive charge and the electrons have a negative charge.
If an atom is by itself, there will be exactly as much positive charge in the nucleus as there is negative charge in the electrons, so the total charge of the atom is zero.
Not all atoms are equally good at holding on to their electrons, however. Some are very good at grabbing electrons (greedy) and some are weak and can't hold on tightly at all. When a greedy atom meets a weak atom, the greedy one can steal an electron from the weak one. If this happens the greedy atom becomes negatively charged since it has an extra electron, and the weak atom becomes positively charged since it is missing an electron.
We now have a positive atom next to a negative atom. These will attract each other since opposite charges attract, which means they will stay together and form a molecule. This kind of sticking together is called "ionic bonding".
A lot of molecules you know about, like the N2 and O2 that make up most of the atmosphere, can't have that type of bond because both atoms are the same type. They have a different type of bond, called "covalent." In covalent bonds, some of the electrons from each atom are shared, and are spread out to partly be around one nucleus and partly around the other.
Most bonds between atoms that aren't exactly alike are sort of part-way in between ionic and covalent.
(republished on 07/13/06)