Some other ions:
Not every element forms ions, during reactions. In fact, out of the first twenty elements in the Periodic Table, only eleven easily form ions. Hydrogen and the metals form positive ions, which have the same names as the atoms. The non-metals form negative ions and their names en in –ide. The other elements do not form ions because their atoms would have to gain or lose several electrons, and that takes too much energy and the other atoms already have full shells.
Transition metal ions:
Some transition metals form only one type of ion. But most of them can form more than one type.
Ions formed from groups of joined atoms are called compound ions. Even though it contains more than one atom each is just one ion.
The Covalent Bond:
When two non-metal atoms react together, both of them need to gain electrons, to reach full shells. They manage this only by sharing electrons between them. Atoms can only share their outer electrons. Because the atoms share electrons, there is a strong force of attraction between them, holding them together. This is called a covalent bond. The bonded atoms form a molecule. A molecule is a small group of atoms which are held together by covalent bonds. Hydrogen gas is made up of hydrogen molecules, and for this reason it is called a molecular substance. When atoms share one pair of electrons its called a covalent bond but when atoms share two pairs of electrons, the bond between them is called a double covalent bond.
A huge number of compounds also exist as molecules. In a molecular compound, atoms of different elements share electrons with each other. These compounds are called covalent compounds because of the covalent bonds in them. Water, ammonia and methane are all covalent compounds.
Ionic and molecular solids:
If the particles in a solid are ions, the solids are called ions solids. If they are molecules, the solids are called molecular or covalent solids. In all ionic solids, the ions are packed together in a regular pattern, and are held together by strong ionic bonds. This means that all solids are crystalline. In all molecular solids, the molecules are held together in a regular pattern; so the solids are crystalline. The forces that hold the molecules together are weak. Ionic solids conduct electricity when melted because the ions are then free to move. Molecular solids do not conduct electricity when melted because molecules are not charged.
The metals and carbon:
In a metal, the atoms are packed tightly together in a regular pattern. The tight packing causes outer electrons to get separated from their atoms. A metal is a lattice of ions in a sea of electrons. Metals are good conductors of electricity because the free electrons can move through the lattice, carrying charge. Diamond is a giant structure of carbon atoms. A carbon atom forms covalent bonds to four others. Each outer atom then bonds to three more, and so on. Eventually millions of carbon atoms are bonded together, in a giant covalent structure. Diamond is very hard-the hardest substance known. This is because each atom is held in place by four strong bonds. It cannot conduct electricity, because there are no ions or free electrons in it too carry charge.
- World Book 99(CD-ROM)(1998) West Monroe St Chicago: IBM