Polar and nonpolar covalent bonds and

molecules

16.3Pages 460-463

Polar Nonpolar Dipole

All have the word “pole” in it, meaning “a part of a system that has opposite positions”

Ex: North Pole and South Pole refers to opposite locations and magnetic fields on earth.

In chemistry Polar refers to oppositely charged sides of a molecule

Vocabulary

Main point- How bad do you want that item? In chemistry this is electronegativity.

Is sharing always equal?

We know the shortcuts for finding out the type of compound and bond formed.

Metal with non-metal = ? Metal with metal = ? Non-metal with non-metal = ?

This shortcut is really based on electronegativity (how much does one atom want the electrons of the other atom)

Electronegativity determines the bond type

Actual values for each atom on page 405

H=2.1 Cl = 3.0 F= 4.0 C= 2.5 Na=0.9

Electronegativity chart

Electronegativity difference

Type of Bond Example

0.0 – 0.4 Nonpolar covalent

H-H or C-H

>0.4-1.9 Polar covalent H-Cl or H-F

> 2.0 Ionic NaCl

When both atoms pull on the electrons equally, the electrons are shared equally.

This happens when both atoms are the same (H2, O2, N2, Cl2, F2, Br2, I2)

It also happens when both atoms have very similar electronegativity values

Ex: C-H, C-C

Nonpolar covalent bonds

Non-polar animation

When the two atoms pull on the electrons unequally.

The more electronegative atom will pull harder and acquire a slight negative charge

The less electronegative atom will pull less and acquire a slight positive charge

This is denoted by a delta (delta +, delta -)

Polar covalent bonds

Polar bond animation

A molecule with one side slightly positive and the other side slightly negative

HCl HF CO H20 NH3

Not polar: CH4 does not have any polar bonds CO2 even though it has polar bonds

Polar molecules

Same atoms on bond = non-polar bond C and H = non-polar bond Every other combination usually polar

Sure solution: Look up electronegativities on page 405 and compare to table on page 463

General Rule for identifying bonds as polar or nonpolar

HW: Fill out the table belowUse the charts on p.405 and p.463

Bonded atoms Difference in electronegativity

Polar or nonpolar covalent bond?

H - H 2.1 – 2.1 = 0 Non-polar

H - C

H - O

H - N

C – C

C - O

C - N

S - Cl

O - N

P - F

Br - Br

Likes dissolve likes is a phrase that tells you which molecules will mix and which will not.

Polar dissolves polar Nonpolar dissolves nonpolar Polar will not mix with nonpolar

Demonstrate with a bottle that has oil and water in it

Demonstrate with two beakers, one water, one oil, and 2 cubes of sugar in each one.

What does the term “likes dissolve likes” mean in regards to polarity?

The 3 intermolecular forces

16.3Pages 463-466

“Intermolecular forces” means “Attractions between molecules”

What does the prefix “inter” mean?

Atoms bond to have complete outer orbitals When they get there, they stop bonding and

become the compound they become If only covalent bonds existed, each little

molecule would be completely independent and every molecular compound would be a ?

Gas! We would have no liquid!!! So there must be OTHER interactions taking place between molecules…

Intermolecular attractions

Van Der Waals Forces◦ 1) London Dispersion forces◦ 2) Dipole-dipole interactions

3) Hydrogen bonds-◦ The strongest of the intermolecular forces

The 3 weak intermolecular forces/attractions

The electrons of amolecule will shift to oneside, creating a temporary dipole. This dipole willcause the other moleculeto create a dipole as welland attraction will occur fora very short time. This occurs between nonpolar molecules

London Dispersion forces

The slightly positive part of one molecule will attract the slightly negative part of another molecule.

This occurs between two polar molecules.

Dipole-dipole forces

The strongest of the 3 intermolecular forces A hydrogen covalently bonded to N, O, or F

will be very electron deficient ( +)

It will become attracted to an unshared pair of a different molecule.

Hydrogen bonding

1) Non-polar vs polar◦ Polarity explains why water and oil do not mix!

Oil is non-polar, Water is polar◦ Polarity explains why water dissolves ionic

compounds!

Why does this matter?

2) Intermolecular forces◦ Explain why liquids and solids exist! ◦ Explains the melting and boiling points of

molecular compounds.◦ Hydrogen bonding explains why water has such

high surface tension! ◦ Helps DNA and proteins take the

shapes that they take!

Why does this matter?

21) You find the difference in electronegativity between the atoms.

<0.4 is nonpolar covalent 0.5-1.9 is polar covalent >2 is ionic

22) dispersion, dipole-dipole, hydrogen bond

23)CCl4 has polar bonds, but is not a polar molecule because of symmetry (it doesn’t have a (+) and (-) side.

24)HOOH, BrCl, HBr, H2O

26)shared bonding electrons, solubility ranges from high to low, exist as molecules

HW:

Polar bond – a covalent bond where electrons are shared unequally◦ The more electronegative atom is slightly negative◦ The less electronegative atom is slightly positive

Non-Polar bond –a covalent bond where electrons are shared equally ◦ Both atoms have similar or identical electronegativity

Dispersion – weak forces caused by the random motion of electrons◦ The only attractions non-polar molecules can have

Dipole-dipole – attractions between polar molecules◦ The slightly positive end of one molecule attracts the slightly negative

end of another

Hydrogen bond – an attraction where a hydrogen (that is bonded to an N, O, or F) is attracted to an unshared pair of electrons on another molecule.◦ The strongest intermolecular attraction of the three