Welcome to the module on Valency and Reactions. 

By the end of this lesson you should be able to: 
1. Use the valency of elements from the periodic table to predict how they combine with other elements. 
2. Form a chemical formula for a substance based on valency. 
3. Explain the difference between ionic and covalent bonds. 
4: Explain the differences between endothermic and exothermic reactions by using a diagram.