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Valence and Binary Compounds

Valence and Binary Compounds. Valence. Def’n: the charge assigned to an atom in a molecule. Example: Note: the first element NaCl is always ‘+’, the second is always ‘-’. -1. +1. The sum of the valences in a molecule must be zero. HCl. N 2. Other examples:. -1. +1. -3.

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Valence and Binary Compounds

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  1. Valence and Binary Compounds

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

  3. HCl N2 Other examples: -1 +1 -3 +3

  4. Some elements have more than one valence • What is the valence of Pb in PbO2? 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+

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

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

  7. Rules • Name the first element regularly and change the ending of the second to “ide” Examples: NaCl – sodium chloride Na2O – sodium oxide CaH2 – calcium hydride

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

  9. Magnesium oxide Mg2+ O2- Mg2O2 reduce to MgO Aluminum chloride Al3+ Cl- AlCl3 Examples

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

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