What is the formula for magnesium chloride?

Review of Formula Writing…

Ions

A positively charged ion is called a cation.

A negatively charged atom is called an anion.

So in an iconic compound the metal is the cation and the non-metal is the anion.

Multivalent Metals

Some metals form more than one type of ion [can have more than 1 type of charge]

We show the charge with a Roman numeral in brackets:

Cu+ … copper (I)Cu2+… copper (II)

Naming Multivalent Metals

What is the name for Fe2O3 ?

Naming Multivalent Metals

What is the name for Fe2O3 ?Net charge has to be zero so…O2- x 3 = -6Fe?+ X 2 = + 66/2 = 3 …so the charge on Fe is 3+

Answer: iron (III) oxide

Writing Formula for Multivalent Metals

What is the formula for chromium (III) oxide ?

Cr3+ Cl-

Cr +3 x 1 = +3Cr -1 x 3 = -3 Net Charge =

0

Final Answer = CrCl3