Bond Types

Chemistry Joke

Q: What do you pay a policeman who works security for a chemistry night class?

A: Copper Nitrate!

Let’s Look At 3 Types of Bonds

• Ionic• Polar Covalent (Molecular)• Nonpolar Covalent

(Molecular)

Remember Electronegativity?

• The tendency for an atom to attract electrons to itself in a bond– The higher the value, the better it is at

attracting electrons.• The difference in the

electronegativity values determines what type of bond will be formed.

ElectronegativityElectronegativityElectronegativity is a scale from 0.7 (Cs) to 4.0 (F).

Electronegativity generally increases across a period and decreases down a group.

Electronegativity Values (write on Periodic Table)

• Why don’t the noble gases have a value?

• They don’t attract electrons!

Ionic Bonds

• If the electronegativity difference is greater than 2.0, one atom will pull the electron completely away from other atom.

• The electrons are NOT shared.• An Ionic BondIonic Bond is formed as + and – attract.• Electronegativity of Na is 0.9; Cl is 3.0.• 3.0 – 0.9 = 2.1; difference > 2.0, so…Ionic!

Polar Covalent Bonds

• Covalent bonds share electrons• The shared pairs are pulled, similar to a

tug-of-war, between the nuclei of the atoms sharing the electrons.

• If the electronegativity difference is between 0.4 – 2.0, one side of the bond becomes slightly more negative and the other side becomes slightly more positive.

• This is a PolarPolar Covalent BondCovalent Bond.

Polar Covalent Bonds

• The electronegativity of H is 2.1; Cl is 3.0.• 3.0 – 2.1 = 0.9; difference is b/w 0.4 – 2.0, so…

Polar Covalent!

ClH∂+ ∂-

Slightly

Polar Covalent Bonds

• The electronegativity of O is 3.5; H is 2.1.• 3.5 – 2.1 = 1.4• Difference is b/w 0.4 – 2.0, so… Polar Covalent!

Nonpolar Covalent Bonds• When the atoms have equal pull, causing the

electrons to be equally shared, the bond is Nonpolar CovalentNonpolar Covalent.

• Neither side of the bond is even slightly positive or negative.

• The electronegativity difference is b/w 0.0 – 0.4. • This is the type of bond that occurs between 2

atoms of the same element. (H2, O2, Cl2, etc.)

Nonpolar Covalent Bonds

• The electronegativity of H is 2.1.

• 2.1 – 2.1 = 0

• The difference is b/w 0.0 – 0.4, so…Nonpolar!

3 Different Types of Bonds

Attractions Between MoleculesVan der Waals ForcesVan der Waals Forces

• Weaker than either the ionic or covalent bonds that form between atoms in a compound.

• Responsible for determining whether a compound is a liquid, gas, or solid

• 3 basic types from weakest to strongest– (London) Dispersion forces– Dipole interaction– Hydrogen bonding

London Dispersion Forces

• Weakest of all molecular attractions• Caused by the motion of electrons producing

a temporary polarity.• Strength of dispersion forces generally

increases as # of electrons in the molecule increases.

• All molecules have these weak attractions.

London Dispersion Forces

Dipole Interaction

• Occurs when polar molecules are attracted to one another

Hydrogen Bonds

• Occurs b/w molecules in which H is covalently bonded to either O, N, or F, which are very electronegative– Causes very polar molecules that are

strongly attracted to each other– Still only has about 5% of the strength

of a covalent bond

Hydrogen BondsVery Important!!• Reason ice is

less dense than water

• Reason for the relatively high b.p. of water

• Responsible for the double helix of the DNA molecule

O

H H

HH

O

+

+

2 lone pairs

Nonpolar or Polar MoleculesMolecules

• We now know how to determine if the bond b/w atom and atom in a compound is polar or nonpolar.

• But…what about the whole molecule?

Nonpolar or Polar MoleculesMolecules

• Draw the Lewis Structure. • If the central atom has any unshared pairs,

the molecule is polar.

Nonpolar or Polar MoleculesMolecules

• If there are no unshared pairs on the central atom, look at the atoms around the central atom.– If they are all the same, the molecule is nonpolar.– If any one of them is different, the molecule is

polar. • In a 2-atom molecule, if the bond between the 2

atoms is polar then the whole molecule is polar.

Nonpolar or Polar MoleculesMolecules

H2O

CO2

HCN

CH3Cl

Polar

Nonpolar

Polar

Polar

N2Nonpolar

HCl

Polar

Chemistry Joke

Q: How do we know that Chuck Norris is not a chemist?

A: The only element he knows is the “element” of surprise!

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