1.  Answer the following questions in full sentences (include question in answer) so that they form notes. 1.Why do atoms bond together? 2.What are 3 ways atoms can become more stable? 3.What type of bond is formed between two atoms when the atoms share valence electrons? 4.Which atoms tend to form covalent bonds? 5.What are three examples of covalently bonded molecules? 6.Why does Helium not form He 2 ? Do Now

2. Y12 Chemistry

3. Gilbert Newton Lewis (October 23, 1875 - March 23, 1946)

4.   Lewis diagrams give us a representation of how atoms combine so that each atom has a stable outer shell  The show only outer valence electrons as they are the electrons involved in bonding What do they show?

5.  Lewis Dot Diagrams for elements

6.   Calculate the number of valence electronsSO2  S has 6 valence electrons  O has 6 valence electrons  6 + 2(6) = 18 Step 1:

7.   Draw the atoms and add 2 bonding electrons (single bond)  Remember the central atom is usually the one with the lowest electronegativity (furthest from F) Step 2: OOS

8.   Fill the valence shell of the outer atoms Step 3: OOS 14 – 12 = 2 e -

9.   Place the remaining electrons around the central atom Step 4: OOS 2-2 = 0 e -

10.   Move pairs of electrons to fill valence shells of all atoms Step 5: OOS A double bond A single bond

11.   Usually the first atom in the compound.  Or H O N C C will be central over N, O, & H N will be central over O & H O will be central over H  If compound has formula X 2 Y then Y will be the central atom.  The least electronegative atom is put in the middle How to know which atom is central

12.   This year would will be dealing mainly with atoms that need either - 2 electrons in their outer shell – Hydrogen  Or 8 electrons in the outer shell – most others  There are two exceptions Molecules that contain Boron = 6 total e.g. BF 3 Beryllium = 4 total Tricks for year 12

13.  Covalent bonding. When atoms s_ _ _ _ p_ _ _ _ of e_ _ _ _ _ _ _ _, the atoms involved must remain close together. The positive charged n_ _ _ _ _ _ of each atom is a_ _ _ _ _ _ _ _ to the negatively charged c_ _ _ _ of electrons between them. This a_ _ _ _ _ _ _ _ _ forms a c_ _ _ _ _ _ _ b_ _ _. When two pairs of electrons are shared we say a d_ _ _ _ _ b_ _ _ has formed. Give an example of a compound that has one of these. Copy and complete sentences