Topic: Covalent Bonding – Lewis Dot Diagrams Do Now: Identify Bond Type from Formula AuAg CO 2 Li 3 NNa 2 S Mg CsF H2OH2O NaCl SO 2 Cu CH 4 CovalentCovalent.

Topic: Covalent Bonding – Lewis Dot Diagrams

Do Now: Identify Bond Type from Formula

AuAgCO2

Li3NNa2SMg

CsFH2ONaCl

SO2CuCH4

Covalent

Covalent

Covalent

Covalent

Ionic

Ionic

Ionic

IonicMetallic

Metallic Metallic

Metallic

Covalent Molecule vs Ionic Compounds

Electrons are shared

Molecules are formed

Electrons are transferred

Ions form = crystal lattice

3 representations of Molecules• Molecular Formula

– tells type and number of atoms

– H2 or O2

• Structural Formula– Shows bonds between atoms– H-H or O=O

• Lewis Dot Diagrams– Shows valence electrons shared between atoms

3 types of bonds• Single Bond – 2 shared valence electrons

– When H or Halogens (F, Cl, I, Br) bond with other atoms (or eachother) they ALWAYS form Single Bonds

3 types of bonds• Single Bond – 2 shared valence electrons

– When H or Halogens (F, Cl, I, Br) bond with other atoms or each other they ALWAYS form Single Bonds

• Double Bonds – 4 shared valence electrons

3 types of bonds• Single Bond – 2 shared valence electrons

– When H or Halogens (F, Cl, I, Br) bond with other atoms or each other they ALWAYS form Single Bonds

• Double Bonds – 4 shared valence electrons

• Triple Bonds – 6 shared valence electrons

Bonding Capacity (# of bonds formed)

00:Ne:Ne, Ar, Kr

22·O:O, S

33·N·N, P

44·C·C, Si

11·F:F, Cl, Br, I

11HH

Bonding Capacity

# Unpaired Electrons

Lewis Structure

Atom

.

..

..

.

....

..

·····

Bonding Capacity (# of bonds formed)

4 3 2 1

H2 H2O CO2

Draw these molecules on your paper…we are going to draw Lewis Dot Diagrams

Rules for drawing Lewis Diagrams1. Arrange symbols on paper the way think atoms are arranged

- Diatomics easy – next to each other- Hydrogens can never be in the middle, always on the outside- Atom with lowest electronegativity placed in center

H2 H2O

H H H O H

CO2

O C O

Rules for drawing Lewis Diagrams2. Add up # valence electrons all atoms

H2 H2O

H H H O H

CO2

O C O

2 8 16

Rules for drawing Lewis Diagrams3. Distribute electrons, start with single bonds (1 pair

of electrons) between all atoms then fill in remaining

H2 H2O

H H H O H

CO2

O C O

2 8 16

Rules for drawing Lewis Diagrams4. 2 tests

1. A) # dots = # valence electrons found in rule 2

2. B) Every atom has octet (8) (except H – only wants 2)

H2 H2O

H H H O H

CO2

O C O

2 8 16Bonding electrons get counted 2 times –once for each atom sharing them

Assessing Lewis Diagrams

• If dot structure passes both tests, you’re finished

• If fails one or both tests, try again

• If single bonds don’t work - try multiple bonds – ALWAYS MOVE PAIR OF ELECTRONS between atoms

CO2

O C O

16

CO2

O C O

16CHECK AGAIN1. A) # dots = # valence

electrons found in rule 2

2. B) Every atom has octet (except H – only wants 2)

O=C=O

Try some examples

• H2, F2, HF, O2, N2

• Step 1: Draw symbols the way think atoms are arranged

–Diatomics easy – atoms next to each other!

Drawing Lewis Diagrams

H H

Step 2: Count up the valence electrons

Each H has 1 valence electron so the total = 2

Step 3: Distribute the valence electrons, starting with single bonds between all atoms

:

Testing Lewis Diagrams

H H:Test 1: 2 dots in diagram = 2 valence electrons

Test 2:Each H has 2 valence electrons (Remember H only wants 2)

Testing Lewis Diagrams

F FStep 1

Step 2 2 X 7 = 14 valence electrons

Step 3 F F: : :..

..

..

..

Try HF

H FStep 1

Step 2 7 + 1 = 8 valence electrons

Step 3 H F: :..

..

O OStep 1:

Step 2: 2 X 6 = 12 valence electrons

Step 3: O O:: :..

..

..

Step 4: Test failed

No Good!

Try O2

Try O2 Again!

O OStep 1:

Step 2: 2 X 6 =12

Step 3: Distribute electrons (single bond between atoms didn't work so try a double bond)

::..

..

..

..

Step 4: Test!

Try N2

N NStep 1:

Step 2: 2 X 5 = 10 electrons

Step 3: Distribute electrons starting with a single bond between the nitrogen atoms

: ..

: .. :

Step 4: Test

No Good!

Try N2 with a double bond

N N::: :..

No Good!

Try N2 with a triple bond

N N:::: :

Step 4: Test