Covalent Bonding – Lewis Dot Diagrams

Packet pages 3-7

Representations of Molecules

Lewis Structures of compoundLewis Structures of compound

HH22 = Molecular Formula = Molecular Formula

H-H = Structural Formula H-H = Structural Formula

[- [- represents 1 pair of shared electronsrepresents 1 pair of shared electrons]]

Halogens

Share 1 pair (2 electrons): form single covalent bondShare 1 pair (2 electrons): form single covalent bond

Single Bonds• Hydrogen and Halogens for Single Bonds

Single bond = 2 electrons are shared

Double Bonds

Oxygen and Sulfur

Double bond = ___ electrons shared

4

Triple Bonds

Triple bond = ___ electrons shared

6

Structure of Covalent Compounds

NOT necessarily empirical - a lot are molecular….we can keep adding atoms!

glucose lipids

C6H12O6 (fats)

STEPS for drawing Lewis Diagrams

1. Arrange symbols on paper the way think atoms are arranged

- Diatomics easy – next to each other- Hydrogens always terminal (on outside)- Atom with least attraction (lowest electronegativity) for shared electrons placed in center

H2

H2OH HH O H

CO2

O C O

Steps for drawing Lewis Diagrams

2. 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 start with single bonds

(electron pairs) between all atoms(electron pairs) between all atoms H2 H2O

H H H O H

CO2

O C O

2 8 16

Rules for drawing Lewis Diagrams4. Test validity (2 tests)

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

2. B) Every atom has octet (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 themBonding 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– Single bond = 2 electrons shared– Double bond = 4 electrons shared– Triple bond = 6 electrons shared

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 HH H

Step 2: Count up the Step 2: Count up the valence electronsvalence electrons

Each H has 1 valence Each H has 1 valence electron so the total = 2electron so the total = 2

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

::

Testing Lewis Diagrams

H HH H::Test 1: Test 1: 2 dots in 2 dots in diagram = diagram = 2 valence 2 valence electronselectrons

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

Testing Lewis Diagrams

F FF FStep 1Step 1

Step 2Step 2 2 X 7 = 14 valence electrons2 X 7 = 14 valence electrons

Step 3Step 3 F FF F:: :: ::....

....

....

....

Try HF

H FH FStep 1Step 1

Step 2Step 2 7 + 1 = 8 valence electrons7 + 1 = 8 valence electrons

Step 3Step 3 H FH F:: ::....

....

O OO OStep 1:Step 1:

Step 2:Step 2: 2 X 6 = 12 valence electrons2 X 6 = 12 valence electrons

Step 3:Step 3: O OO O:::: ::....

....

....

Step 4: Test failedStep 4: Test failed

No Good!No Good!

Try O2

Try O2 Again!

O OO OStep 1:Step 1:

Step 2:Step 2: 2 X 6 =122 X 6 =12

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

::::....

....

....

....

Step 4: Test!Step 4: Test!

Try N2

N NN NStep 1:Step 1:

Step 2:Step 2: 2 X 5 = 10 electrons2 X 5 = 10 electrons

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

: : ....

:: .... ::

Step 4: TestStep 4: Test

No Good!No Good!

Try N2 with a double bond

N NN N:::::: ::....

No Good!No Good!

Try N2 with a triple bond

N NN N:::::::: ::

Step 4: TestStep 4: Test