Valence and Binary Compounds

Valence Def’n: the charge assigned to an atom in a molecule. Example:Note: the first element NaClis always ‘+’, the second is always ‘-’ +1 The sum of the valences in a molecule must be zero.

Other examples: HCl N

Some elements have more than one valence What is the valence of Pb in PbO 2 ? Answer: O is 2 - and since there are two oxygens, the overall charge is –4. So Pb is 4 + What is the valence of Pb in PbO? Answer: O is 2 -, so Pb is 2 +

Use the green sheet to see the elements that have multiple valences!

Naming Simple Binary Compounds When do you use this: The first element only has one valence. Naming compounds with 2 elements.

Rules 1.Name the first element regularly and change the ending of the second to “ide” Examples: NaCl – sodium chloride Na 2 O – sodium oxide CaH 2 – calcium hydride

Writing the Formulas 1.Determine the valence of each element. 2.Crisscross the valences and write them as subscripts. 3.Reduce to simplest ratio.

Examples Magnesium oxide Mg 2+ O 2- Mg 2 O 2 reduce to MgO Aluminum chloride Al 3+ Cl - AlCl 3

Valences of 1 are not written in final version of the chemical formula.