Covalent bondingCovalent bonding

Covalent bondsCovalent bonds

Nonmetals hold onto their valence electrons.Nonmetals hold onto their valence electrons. They can’t give away electrons to bond.They can’t give away electrons to bond. Still want noble gas configuration (full outer energy Still want noble gas configuration (full outer energy

level).level). Get it by Get it by sharingsharing valence electrons with each valence electrons with each

other.other. By sharing, both atoms get to count the electrons By sharing, both atoms get to count the electrons

toward noble gas configuration.toward noble gas configuration.

How does HHow does H22 form? form?

+ +

The nuclei repel

But they are attracted to electrons

They share the electrons

Electron Dot diagramsElectron Dot diagrams

A way of keeping track of A way of keeping track of valence electrons.valence electrons.

How to write themHow to write them

1)1) Write the symbol.Write the symbol.

2)2) Put one dot for each Put one dot for each valence electronvalence electron

3)3) Don’t pair up until they Don’t pair up until they have tohave to

X

The Electron Dot diagram for Nitrogen

Nitrogen has 5 valence electrons.

First we write the symbol.

NThen add 1 electron at a time to each side...Until they are forced to pair up.

Your Turn to TryYour Turn to Try

Fill in the chart on the top of page 5 in your Fill in the chart on the top of page 5 in your packet.packet.

•Electron Dot Electron Dot NotationNotation

Bonding Sites:Bonding Sites:H, 1*H, 1*Be, 2*Be, 2*B, 3*B, 3*C, 4C, 4N, 3N, 3O, 2O, 2F, 1F, 1

Ne, 0Ne, 0He, 0He, 0

Covalent bondingCovalent bonding

Fluorine has seven valence electronsFluorine has seven valence electrons

F

•A second atom also has seven

F

By sharing electrons…both end with full orbitals

8 Valence electrons

8 Valence electrons

Single Covalent BondSingle Covalent Bond

A sharing of two valence electrons.A sharing of two valence electrons. Only nonmetals and Only nonmetals and Hydrogen.Hydrogen. Different from an ionic bond because they Different from an ionic bond because they

actually form molecules.actually form molecules. Two specific atoms are joined.Two specific atoms are joined.

How to show how they formedHow to show how they formed

It’s like a jigsaw puzzle.It’s like a jigsaw puzzle. I have to tell you what the final formula is.I have to tell you what the final formula is. You put the pieces together to end up with You put the pieces together to end up with

the right formula.the right formula. For example- show how water is formed For example- show how water is formed

with covalent bonds.with covalent bonds.

WaterWater

H

O

Each hydrogen has 1 valence Each hydrogen has 1 valence electronelectron

Each hydrogen wants 1 moreEach hydrogen wants 1 more

The oxygen has 6 valence The oxygen has 6 valence electronselectrons

The oxygen wants 2 moreThe oxygen wants 2 more

They share to make each other They share to make each other happyhappy

WaterWater

Put the pieces togetherPut the pieces together The first hydrogen is happyThe first hydrogen is happy The oxygen still wants one moreThe oxygen still wants one more

H O

WaterWater

The second hydrogen attachesThe second hydrogen attaches Every atom has full energy levelsEvery atom has full energy levels

H OH

Multiple BondsMultiple Bonds

Sometimes atoms share more than one pair Sometimes atoms share more than one pair of valence electrons.of valence electrons.

A double bond is when atoms share two pair A double bond is when atoms share two pair (4) of electrons.(4) of electrons.

A triple bond is when atoms share three pair A triple bond is when atoms share three pair (6) of electrons.(6) of electrons.

Carbon dioxideCarbon dioxide COCO22 - - Carbon is central Carbon is central

atomatom Carbon has 4 valence Carbon has 4 valence

electronselectrons Wants 4 moreWants 4 more Oxygen has 6 valence Oxygen has 6 valence

electronselectrons Wants 2 moreWants 2 more

O

C

Carbon dioxideCarbon dioxide

Attaching 1 oxygen leaves the oxygen 1 Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 shortshort and the carbon 3 short

OC

Carbon dioxide Attaching the second oxygen leaves

both oxygen 1 short and the carbon 2 short

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more

OCO

Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO

Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO8 valence electrons

Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO8 valence electrons

Carbon dioxide The only solution is to share more Requires two double bonds Each atom gets to count all the atoms in

the bond

OCO

8 valence electrons

How to draw themHow to draw them

Add up all the valence electrons.Add up all the valence electrons. Count up the total number of electrons to Count up the total number of electrons to

make all atoms happy (i.e. # of bonding sites)make all atoms happy (i.e. # of bonding sites) Subtract.Subtract. Divide by 2Divide by 2 Tells you how many bonds - draw them.Tells you how many bonds - draw them. Fill in the rest of the valence electrons to fill Fill in the rest of the valence electrons to fill

atoms up.atoms up.

ExamplesExamples

NHNH33

N - has N - has 55 valence e valence e-,-, wants wants 88 H - has 1 valence eH - has 1 valence e-,-, wants wants 22

NHNH3 3 hashas 55+1(x 3) = 8 e+1(x 3) = 8 e--

NHNH3 3 wantswants 88++22(x3) = 14 e(x3) = 14 e--

(14-8)/2= 3 bonds(14-8)/2= 3 bonds 4 atoms with 3 bonds4 atoms with 3 bonds

N

H

N HHH

ExamplesExamples Draw in the bondsDraw in the bonds All 8 electrons are accounted forAll 8 electrons are accounted for Everything is full, Nitrogen has a lone pair of Everything is full, Nitrogen has a lone pair of

electronselectrons

ExamplesExamples

HCN C is central atomHCN C is central atom N - has 5 valence electrons wants 8N - has 5 valence electrons wants 8 C - has 4 valence electrons wants 8C - has 4 valence electrons wants 8 H - has 1 valence electrons wants 2H - has 1 valence electrons wants 2

HCNHCN has 5+4+1 = 10has 5+4+1 = 10

HCNHCN wants 8+8+2 = 18wants 8+8+2 = 18

(18-10)/2= 4 bonds(18-10)/2= 4 bonds 3 atoms with 4 bonds -will require multiple bonds - 3 atoms with 4 bonds -will require multiple bonds -

not to Hnot to H

HCNHCN

Put in single bondsPut in single bonds Need 2 more bondsNeed 2 more bonds Must go between C and NMust go between C and N

NH C

HCN Put in single bonds Need 2 more bonds Must go between C and N Uses 8 electrons - 2 more to add

NH C

HCN Put in single bonds Need 2 more bonds Must go between C and N Uses 8 electrons - 2 more to add Must go on N to fill octet

NH C

Another way of indicating Another way of indicating bondsbonds

Often use a line to indicate a bondOften use a line to indicate a bond Called a structural formulaCalled a structural formula Each line is 2 valence electronsEach line is 2 valence electrons

H HO =H HO

Structural ExamplesStructural Examples

H C N

C OH

H

C has 8 electrons C has 8 electrons because each because each line is 2 electronsline is 2 electrons

Ditto for NDitto for N

Ditto for C hereDitto for C here Ditto for ODitto for O

Ionic CompoundsIonic Compoundselectron dot structureselectron dot structures

Write as an equation. Write as an equation. Reactants-EACH atom with dotsReactants-EACH atom with dots

Products-EACH ion with its charge and Products-EACH ion with its charge and dotsdots

Example: Example:

Lewis DotsLewis DotsIonic CompoundsIonic Compounds

For homework tonight, use the “equation” For homework tonight, use the “equation” method for question 38, p 176 if it helps you method for question 38, p 176 if it helps you determine the products.determine the products.

The ONLY thing required for an answer The ONLY thing required for an answer would be the products….would be the products….