Final answer:
The oxidation number for Magnesium (Mg) in its ion form is +2, where it loses two electrons when forming compounds like MgCl2. In this reaction, Mg is oxidized and Cl is reduced as they achieve their respective oxidation states.
Step-by-step explanation:
The oxidation number for Magnesium (Mg) in a monatomic ion, such as in MgCl2, is +2. This is determined using the periodic table where Magnesium is located in the second group and typically loses two electrons to achieve a noble gas configuration. The Lewis dot diagram for Mg would simply have no dots around it because Mg2+ has lost its two valence electrons. The chloride ion (Cl−), on the other hand, has an oxidation number of -1 in MgCl2.
When Mg reacts with Cl2 to form MgCl2, there is a transfer of electrons. Mg loses two electrons and is oxidized, thus changing its oxidation state from 0 to +2. Each Cl atom gains one electron to become Cl−, changing its oxidation state from 0 to -1.