How Atoms Combine

All atoms “want” their valence shell to be like a noble gas -- full and stable. (having 8 or 2 electrons)

All atoms “want” their valence shell to be like a noble gas -- full and stable. (having 8 or 2 electrons) Atoms will gain, lose or share electrons to get these 8 (or 2) in their outer shell.

2 kinds of chemical bonds: Covalent: formed when atoms share electrons in their valence shell.

2 kinds of chemical bonds: Covalent: formed when atoms share electrons in their valence shell. Ionic: formed when atoms transfer electrons. One element gives an electron up, the other element takes it.

Ionic bond

Compound: A substance formed when 2 or more elements combine chemically.

Compound: A substance formed when 2 or more elements combine chemically. Elements in a compound always combine in the same ratio--The Law of Constant Proportions.

Chemical formulas Represent compounds Tells how many of each atom there is in a compound.

Oxidation number Name given to the combining ability of an atom. Indicates how many electrons an atom has gained or lost. Charge of an ion when it has gained or lost electrons. Mg+2 Cl-1