1. Part Two
Reactions and Bonding

2. Though the periodic table has only 118 or so elements, there are obviously many more substances in nature than 118 pure elements. This is because atoms can react with one another to form new substances called compounds. Formed when two or more atoms chemically bond together, the resulting compound is unique both chemically and physically from its parent atoms.
EXAMPLE:
The element sodium is a silver-colored metal that reacts so violently with water that flames are produced when sodium gets wet.
The element chlorine is a greenish-colored gas that is so poisonous that it was used as a weapon in World War I. 
  When chemically bonded together, these two dangerous substances form the compound sodium chloride, a compound so safe that we eat it every day - common table salt!
Likewise, Oxygen (gas) and Hydrogen (gas) on their own make one of the most flammable situations ever. But when they bond they produce a liquid which is something that all living things need – water! – A perfect example of how a compound can be extremely different from it’s parent atoms!

3. In 1916, the American chemist Gilbert Newton Lewis proposed that chemical bonds are formed between atoms because electrons from the atoms interact with each other. Lewis had observed that many elements are most stable when they contain eight electrons in their valence shell.
He suggested that atoms with fewer than eight valence electrons bond together to share electrons and complete their valence shells.
Valence Shell - The outermost orbit of the electrons in an atom. They are the least tightly bound to the nucleus and thus can be removed easily.
BONUS:
What element is the above atom animation?
The bonding of atoms to make compounds is made possible by these electrons. There are two main types of bonding atoms take part in:

4. Ionic Bonding In ionic bonding, electrons are completely transferred from one atom to another. In the process of either losing or gaining negatively charged electrons, the reacting atoms form ions. The oppositely charged ions are attracted to each other by electrostatic forces, which are the basis of the ionic bond. Such bonds occur between metals and nonmetals and result in a solid.
Questions:
1. What atoms are involved in this example?
2. What charges do these atoms originally have?
3. Why does the green atom want an electron?
4. Which atom becomes ionized?
5. What is it that brings these atoms together?
6. What compound is produced in this bond?

5. Atoms ultimately want their valence shell “filled” to its max in order to gain additional stability. This electron number depends on the element.
Covalent Bonding Covalent bonding occurs when two (or more) elements share electrons. Both atoms want an additional electron to fill their valence shell, and when they share, both get what they want. These bonds occur between nonmetals and form gases and liquids.
QUESTIONS:
1. What atoms are these?
2. How many electrons does each want in it’s valence shell to be stable?
3. How many electrons must orbit an inner shell of these atoms?
4. What would be the symbol for this compound?
5. Why would this type of bond be weaker than an ionic bond?