Covalent Bonds

Unit 11

Covalent Bonds• Involve sharing outer energy level

electrons.

How Are They Different Than Ionic?

• Ionic bonds work by electromagnetic attraction. A positively charged ion is attracted to a negative ion.

• Covalent bonds work by sharing electrons. They do not have charges, but are hard to separate due to this sharing.

ClClHow will two chlorine atoms react?

ClClEach chlorine atom wants to gain one electron to achieve an octet

Cl Cl

Cl Cl

Cl Cl

Cl Cloctet

Cl Cl

circle the electrons foreach atom that completestheir octets

octet

Cl Cl

circle the electrons foreach atom that completestheir octets

The octet is achieved byeach atom sharing theelectron pair in the middle

Cl Cl

circle the electrons foreach atom that completestheir octets

The octet is achieved byeach atom sharing theelectron pair in the middle

Cl Cl

circle the electrons foreach atom that completestheir octets

This is the bonding pair

Cl Cl

circle the electrons foreach atom that completestheir octets

Single bonds are abbreviatedwith a dash

Cl Cl

circle the electrons foreach atom that completestheir octets

This is the chlorine molecule,

Cl2

Covalent Bonds• Each oxygen has 6 valence

electrons and wants two more to have a full octet.

6 electrons6 electrons

Covalent Bonds• If one oxygen shares two

electrons with the other, the other has a full octet.

8 electrons – happy!4 electrons left

Covalent Bonds• But, then the other oxygen is

short, so it pulls them back.• Now the other oxygen shares 2

electrons4 electrons left8 electrons – happy!

Covalent Bonds• Thus, by each of them sharing

two electrons back and forth, they both are at the full octet simultaneously.

8 electrons8 electrons

OO

OO

OO

OO

OOBoth electron pairs are shared.

OOBoth electron pairs are shared.

So Who Covalently Bonds?

• Alkaline or Alkali Earth Metals do not form covalent bonds!

• Also Halogens are rarely covalently bonded.• Mostly it is non-metals in groups 3,4,5, and 6

Electron Distribution

C.

...

Electrons occur in 4 fours separated as far

apart as possible

Valence Electrons: 4

Electron Distribution

N ... C

...

.Electrons occur in 4

fours separated as far apart as possible

Valence Electrons: 4 5

Electron Distribution

N ... C

...

. ..OElectrons occur in 4

fours separated as far apart as possible

Valence Electrons: 4 5 6

Electron Distribution

N ... C

...

. ..OElectrons occur in 4

fours separated as far apart as possible

Secret Question: Why do electrons first fill orbitals one at a time before pairing up?

Valence Electrons: 4 5 6

Electron Distribution

N ... C

...

. ..OElectrons occur in 4

fours separated as far apart as possible

Secret Question: Why do electrons first fill orbitals one at a time before pairing up?It is because electrons repel each other and want to be as far apart as possible.

Valence Electrons: 4 5 6

Exception to Octet Rule

• Boron only has 3 valence electrons, so it is impossible to get to eight via covalent bonding

• Without 4 valence electrons, the shape of the molecule flattens out.

B

..

. BH3

Single Bond

• Ethane is C2H6

Double Bond

• Ethene is C2H4

Triple Bond

• Acetylene is C2H2

Quadruple Bond???

• Can not occur, because the last bond can not bend all the way around.

Too far to bend

Too far to bend

Especially since triple bonds are so rigid

Possible Covalent Bonds• Only where single electrons are located, can covalent bonds

be made.• Carbon has 4 single electrons, thus it can make 4 bonds.

• Nitrogen has 3 single electrons, thus it can make 3 bonds.

• Oxygen has 2 single electrons, thus it can make 2 bonds.

Double Bonds Revisited

• Since Oxygen can make two bonds, and Carbon can make four, it makes for some interesting combinations.

Why Carbon is the Key to Life• It is precisely because carbon can make 4 bonds, as

well as, double and triple bonds, that makes it so critical to life.

• Carbon chains can form virtually every formation possible.

DNA and the building blocks for life

• Carbon, plus two other flexible elements, oxygen and nitrogen form the backbone of DNA

• DNA contains the genetic code for the building of life out of the largest of all molecules, proteins.

Proteins are the largest molecules known