Covalent BondsCovalent Bonds

Forming single, double, and triple Forming single, double, and triple bondsbonds

Covalent BondingCovalent Bonding

Remember, when atoms bond covalently, Remember, when atoms bond covalently, there is a sharing of electrons between the there is a sharing of electrons between the two atoms. two atoms.

However, not all of the electrons are However, not all of the electrons are involved in the bond, so there are two involved in the bond, so there are two different types of electron pairs.different types of electron pairs. Bonding Pair: Bonding Pair: Shared Shared (shown by (shown by lineslines)) Lone Pairs: Lone Pairs: Unshared Unshared (shown by pairs of (shown by pairs of

dotsdots))

There are also a few There are also a few types of covalent bonds types of covalent bonds and the type of covalent and the type of covalent bond depends on how bond depends on how many pairs of electrons many pairs of electrons

are shared. are shared.

Single Covalent BondsSingle Covalent Bonds

The sharing of ______ pair of electronsThe sharing of ______ pair of electrons1

Double Covalent BondsDouble Covalent Bonds

Triple Covalent BondsTriple Covalent Bonds

The sharing of ______ pair of electronsThe sharing of ______ pair of electrons

The sharing of ______ pair of electronsThe sharing of ______ pair of electrons

2

3

Strength of Bonds Strength of Bonds

Distance separating nuclei - _________ Distance separating nuclei - _________ ______________________

Depends on the size of the atoms - Depends on the size of the atoms - _________ ____________________ ___________

Pairs shared – more electrons shared, Pairs shared – more electrons shared, _________ ___________ _________ ___________

(_____________ has smallest bond (_____________ has smallest bond length)length)

Smaller bond length - _________ Smaller bond length - _________ ______________________

bondlength

radii

closer together

atomic

Triple bond

bondstronger

Strength of BondsStrength of Bonds

Bond dissociation energy – energy to Bond dissociation energy – energy to _________ ____________________ ___________

Energy must be _________ to break Energy must be _________ to break bondsbonds

Direct relationship between bond energy Direct relationship between bond energy and bond length - _________ bond length, and bond length - _________ bond length, _________ bond, _________ bond energy_________ bond, _________ bond energy

bondsbreakadded

smallerstronger more

So, how do scientists So, how do scientists decide how many decide how many

electrons are shared? electrons are shared? One way is by drawing One way is by drawing

Structural Formulas Structural Formulas a.k.a. a.k.a. Lewis FormulasLewis Formulas

Rules:Rules:1.1. Add up total number of ________ electrons.Add up total number of ________ electrons.2.2. Place atoms on center or sides....how? Place atoms on center or sides....how?

3.3. Connect each atom with a _________ bond, Connect each atom with a _________ bond, then subtract from total number (2 per line).then subtract from total number (2 per line).

4.4. If any electrons are left, place pairs of If any electrons are left, place pairs of electrons on the __________ atom(s) until electrons on the __________ atom(s) until they are “___________”.they are “___________”.Remember, Hydrogen can only make Remember, Hydrogen can only make ____________________________

valence

single

one single bond

Single element in center firstLeast electronegative in center if there is a choice Hydrogen is never in the middle

happyoutside

5. If any electrons are left, place them on the 5. If any electrons are left, place them on the centercenter atom. atom.

6. When you are at 0 pairs, make sure 6. When you are at 0 pairs, make sure everyone is “happy”: everyone is “happy”:

• Happy Hydrogen :____________ Happy Hydrogen :____________ • Happy everyone else:__________Happy everyone else:__________

7. Remember a line represents ___ electrons.7. Remember a line represents ___ electrons.

8. If everyone is happy then.....8. If everyone is happy then.....FinishedFinished. If . If everyone is not happy then you must everyone is not happy then you must share extra pairs and form share extra pairs and form doubledouble or even or even tripletriple bonds. bonds.

2 electrons8 electrons

2

Let’s try some examplesLet’s try some examples

HH22OO

CFCF44

NClNCl22BrBr

COCO22

Polyatomic IonsPolyatomic Ions

1.1. Take Take chargecharge into consideration. (Add into consideration. (Add negativenegative to total, subtract to total, subtract positivepositive from from total of electrons.)total of electrons.)

2.2. Put Put bracketsbrackets around structure with around structure with chargecharge on on outside rightoutside right corner corner

Let’s look at COLet’s look at CO332- 2- and NHand NH44

+1+1