The document outlines 10 rules for assigning oxidation numbers to elements in chemical compounds: 1) Cations are written first followed by anions with oxidation numbers of +1 for cations and -1 for anions like H in HCl. 2) Free elements have an oxidation number of 0 like He and N2. 3) The oxidation number of a monatomic ion equals its charge like +1 for Na+ and -3 for N3-. 4) Hydrogen's oxidation number is usually +1 except in metal hydrides where it is -1. Oxygen is usually -2 except in compounds like H2O2. Group 1A elements are +1 and Group 2A elements

1. CHEMISTRY I Chapter 16 Rules for Assigning Oxidation Numbers

2. Rules for Assigning Oxidation Numbers 1. The cation is written first in a formula, followed by the anion. For example, in NaH, the H is H -1 ; in HCl, the H is H +1 . 2. The oxidation number of a free element is always 0. The atoms in He and N 2 , for example, have oxidation numbers of 0.

3. Rules for Assigning Oxidation Numbers 3. The oxidation number of a monatomic ion equals the charge of the ion. For example, the oxidation number of Na + is +1; the oxidation number of N 3- is -3. 4. The usual oxidation number of hydrogen is +1. Except in metal hydrides is -1 The For example, in HI, H is +1 but in NaH, H is -1

4. Rules for Assigning Oxidation Numbers 5. The oxidation number of oxygen in compounds is usually -2. Exceptions include H 2 O 2 , where O is -1

5. Rules for Assigning Oxidation Numbers 6. The oxidation number of a Group IA element in a compound is +1. The oxidation number of a Group IIA element in a compound is +2.

6. Rules for Assigning Oxidation Numbers 7. The oxidation number of a Group VIIA element in a compound is -1, except when that element is combined with one having a higher electronegativity. The oxidation number of Cl is -1 in HCl, but the oxidation number of Cl is +1 in HOCl.

7. Rules for Assigning Oxidation Numbers 8. The sum of the oxidation numbers of all of the atoms in a neutral compound is 0. 9. The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion. For example, the sum of the oxidation numbers for SO 4 2- is -2.

8. Rules for Assigning Oxidation Numbers 10. The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion. For example, the sum of the oxidation numbers for SO 4 2- is -2.