Writing chemical formulas: 1 Writing chemical formulas: 1. When a positive ion charge and a negative ion charge have the same number, they fit together in a 1:1 proportion. Ex. Li+1 and Cl-1 react to create LiCl. Ex. Mg+2 and O-2 react to create MgO. Ex. Al+3 and N-3 react to create AlN.

Li Cl Mg O Al N

2. When the ion charge numbers are not the same, you must balance them by fitting them together in opposite proportions to the charge. Ex. Li1+ and O2- react to create Li2O. Two lithium ions bind to one oxygen atom, each giving up one electron to fill oxygen’s shell. Ex. Na+1 and P3- react to create Na3P. Three sodium ions bind to one phosphorus ion, each giving up one electron to fill phosphorus’ shell.

Li O Li P Na Na Na

Ex. Be2+ and N3- react to create Be3N2 Ex. Be2+ and N3- react to create Be3N2. Three beryllium atoms give up 2 electrons each to fill up the shell of two nitrogen atoms. REMEMBER THAT THE METAL ION IS ALWAYS WRITTEN FIRST, SO THAT MEANS ON THE LEFT.

Be N Be N Be

Some atoms have more than one ion charge. They are called multivalent. They only occur after the element 20. The compound changes based on which ion charge is used. Ex. Fe3+ and P3- react to create FeP. Ex. Fe2+ and P3- react to create Fe3P2.

REMEMBER THAT WHEN YOU ARE SOLVING A PROBLEM THE ION CHARGE IS NOT ACTUALLY WRITTEN BESIDE THE ELEMENT NUMBER. Ex. P3- will be written as a neutral atom, so P. YOU MUST LOOK IT UP IN YOUR PERIODIC TABLE OF ELEMENTS!!!

Naming Chemical Formulas 1. Never change the name of the metal. It always stays the same. 2. Change the ending of the non-metal name to “-ide”. Ex. Chlorine becomes chloride. NaCl = Sodium chloride Ex. Nitrogen becomes nitride. Be3N2 = Beryllium nitride Ex. Phosphorus becomes phosphide. - K3P = Potassium phosphide.

4. For a multivalent metal, indicate using brackets and roman numerals what the valence, (charge), of the ion is. The bracket is place in between the metal and the non-metal. Ex. Fe3P2 is written as Iron(II)Phosphide. Ex. FeP is written as Iron(III)Phosphide.