Oxidation Number E199Cd

1. **Problem Statement:** You want to learn the rules for determining oxidation numbers in chemical compounds. 2. **Definition:** The oxidation number (or oxidation state) of an atom is the charge it would have if all bonds to atoms of different elements were 100% ionic. 3. **Important Rules:** - The oxidation number of an element in its elemental form is always $0$. - For a monoatomic ion, the oxidation number equals the ion charge. - Oxygen usually has an oxidation number of $-2$ in compounds, except in peroxides where it is $-1$. - Hydrogen usually has an oxidation number of $+1$ when bonded to nonmetals and $-1$ when bonded to metals. - The sum of oxidation numbers in a neutral compound is $0$. - The sum of oxidation numbers in a polyatomic ion equals the ion's charge. 4. **Example:** In water, $H_2O$: - Hydrogen is $+1$ each, so total $+2$. - Oxygen is $-2$. - Sum: $2 \times (+1) + (-2) = 0$ which matches the neutral molecule. 5. **Summary:** Use these rules step-by-step to assign oxidation numbers to atoms in compounds, helping to understand redox reactions and electron transfer.