H 2O, CH 4) always has an oxidation state of +1 except in metal hydrides (e.g. MgO, CaSO 4) have fixed oxidation state of +2. NaCl, K 2O) have fixed oxidation state of +1. #5 Some elements have a fixed oxidation state in their compounds In OH – ion, oxygen atom has an oxidation state of -2 while hydrogen atom has an oxidation state of +1. #4 The sum of the oxidation states of all the atoms in a polyatomic ion is the same as the charge on the ion.Į.g.

In CCl 4, carbon atom has an oxidation state of +4 while each chlorine atom has an oxidation state of -1. In MgO, magnesium atom has an oxidation state of +2 while oxygen atom has an oxidation state of -2.Į.g. #3 The oxidation states of the atoms in compound add up to zero.Į.g. Oxygen atom in O 2- ion has an oxidation state of -2. Sodium atom in Na + ion has an oxidation state of +1.Į.g. #2 The oxidation state of a simple ion is the same as the charge on the ion.Į.g. Each oxygen atom in O 2 has an oxidation state of 0. Each iodine atom in I 2 has an oxidation state of 0. Copper atom in Cu has an oxidation state of 0.Į.g. #1 The oxidation state of an element is always zero.Į.g. To work out the oxidation state, we must apply the following rules. Determining the oxidation states of the reacting atoms is an excellent way to determine whether oxidation or reduction has taken place. When a substance loses or gains electrons, its oxidation state changes. Note that this is true even for covalent molecule. The oxidation state is defined as the charge of an atom of an element would have if it existed as an ion in a compound. It is actually quite easy if you observe several rules when it comes to assigning oxidation states.

Directions: In the following questions, give the oxidation number of the indicated atoms/ion.Are you struggling to determine the oxidation states of elements in chemical reactions and thus unable to decide if a particular chemical reaction is a redox reaction or not? The sum of the oxidation numbers of all the elements in a polyatomic ion equals the charge on the ion. The sum of the oxidation number of all the elements in a compound equals 0. The oxidation number of an element in a monatomic ion equals the charge of the ion. A pure element has an oxidation number of 0. WORKSHEET – ASSIGNING OXIDATION NUMBERS Name _

Assigning oxidation numbers worksheet