1. Chemical Compounds: Part II

2. Naming Binary Molecular Compounds  Molecular compounds are composed of individual covalently bonded units or molecules  Two systems of nomenclature Old System – Prefixes Stock System – Uses Oxidation Numbers

3. Prefix System NumberPrefix 1Mono- 2Di- 3Tri- 4Tetra- 5Penta- 6Hexa- 7Hepta- 8Octa- 9Nona- 10Deca-

4. Prefix System  Rules 1. The less electronegative element is given first. It is given a prefix only if it contributes more than one atom to a molecule of the compound.

5. Prefix System 2. The second element is named by combining (a) a prefix indicating the number of atoms contributed by the element (b) the root of the name of the second element (c) the ending –ide.

6. Prefix System 3. Drop o or a at end of prefix when root word of element begins with a vowel.  Example – P 4 O 10 tetraphosphorus decoxide

7. Acids and Salts  Acids – most are binary or oxyacids  Binary acids – consist of two elements, usually hydrogen and one of the halogens  Oxyacids – contain hydrogen, oxygen, and a third element (usually a nonmetal)

8. Acids and Salts  In chemical nomenclature, the term acid usually refers to a water solution of the compound rather than the compound itself Example – hydrochloric acid – a water solution of the molecular compound hydrogen chloride, HCl

9. Acids and Salts  Many polyatomic ions are produced by the loss of hydrogen ions from oxyacids Sulfuric Acid H 2 SO 4 SulfateSO 4 2- Nitric AcidHNO 3 NitrateNO 3 1- Phosphoric Acid H 3 PO 4 PhosphatePO 4 3-

10. Acids and Salts  Some salts contain anions in which one or more hydrogen atoms from the acid are retained. Such anions are named by adding the word hydrogen or the prefix bi- to the anion name. Example - H 2 CO 3 – carbonic acid  HCO 3 - – hydrogen carbonate ion or bicarbonate ion

11. Oxidation Numbers  Oxidation numbers aka oxidation states are assigned to the atoms composing the compound or ion – these are used in order to indicate the general distribution of electrons among the bonded atoms in a molecular compound or a molecular ion

12. Oxidation Numbers  Oxidation numbers do not have an exact physical meaning. However, they are useful in naming compounds, writing formulas, and balancing equations.

13. Assigning Oxidation Numbers  Shared electrons are assumed to belong to the more-electronegative atom in each bond.  Rules 1. The atoms in a pure element have an oxidation number of zero.

14. Assigning Oxidation Numbers 2. The more electronegative element in a binary molecular compound is assigned the number equal to the negative charge it would have as an anion. The less electronegative element is assigned the number equal to the positive charge it would have as a cation. 3. Fluorine has an oxidation number of -1 in all of its compounds (most electronegative element).

15. Assigning Oxidation Numbers 4. Oxygen has an oxidation number of -2 in almost all compounds Exceptions – in peroxides such as H 2 O 2 in which it is -1, and in compounds with halogens such as OF 2 which it is +2

16. Assigning Oxidation Numbers 5. Hydrogen - +1 in all compounds containing elements that are more electronegative than it; -1 in compounds with metals. 6. The algebraic sum of the oxidation numbers of all atoms in a neutral compound is equal to zero 7. The algebraic sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the charge of the ion.

17. Assigning Oxidation Numbers 8. Although rules 1-7 apply to covalently bonded atoms, oxidation numbers can also be assigned to atoms in ionic compounds.  A monatomic ion has an oxidation number equal to the charge of the ion

18. How do we use oxidation numbers?  Suppose you want to know the formula of a binary comound formed between sulfur and oxygen  Look at common oxidation states of sulfur +4, +6 so maybe SO 2 or SO 3 (Remember oxidation numbers alone cannot be used to predict the existence of a comound)

19. How do we use oxidation numbers?  Stock System Nomenclature FormulaPrefix SystemStock System SO 2 Sulfur dioxideSulfur (IV) oxide SO 3 Sulfur trioxideSulfur (VI) oxide