How do I balance Magnesium + Chlorine --> Magnesium Chloride?

Question

Help would be greatly appreciated!

Answer 1

Mg + Cl2 = MgCl2

Answer 2

The balanced reaction is:
Mg + Cl2 --> MgCl2

But you are asking how one would know that the above reaction is correct.

Magnesium is an alkaline-Earth metal (the 2nd column over from the left on the periodic table) and wants very much to loose two electrons so that it can have a noble gas configuration, so Magnesium will becomes the Mg+2 ion.
Chlorine is a halogen (2nd column over from the right on the periodic table) and wants to gain 1 electron so that it can have a stable noble gas configuration and become the Chlorine ion (Cl-).

Chlorine wants to gain an electron and have a -1 charge.
Magnesium wants to loose 2 electrons and have a +2 charge.
The overall charge on the compound, Magnesium Chloride, must be zero so the two ions must combine in such a ratio so that the +2 charges from the Magnesiums cancel out the -1 charges from the Chlorides.
For every one Mg+2 ion, 2, Cl- ions are required to balance out the charge, so the Magnesium Chloride formula unit is written as MgCl2.

Once you know the chemical formula of the products, it is just a matter of balancing out the reaction to make sure that the number of Magnesiums and Chlorines on the product side equal those on the reactant side, which is easy in this case due to the simplicity of the reaction, so extra coefficients are needed.
Also, Chlorine is a diatomic element and will not be found as a free atom under normal circumstances, so instead of reaction two moles of atomic Chlorine with Magnesium, we need to react 1 mole of Chlorine gas since that is the form that Chlorine will be in during this reaction.

Answer 3

Mg +Cl2 >>MgCl2
The reaction is balanced