H N H

Do now:Explain the shape and bond angle of an ammonia (NH3) molecule.

H• Shape• Bond angle• Regions around N• Explanation of regions repelling each other to get as far away

from each other as possible• Bonding and non-bonding regions

ElectronegativityHow well an atom can attract electrons towards itself.

A calculated number between 0 and 4. The higher the number the more an electron can attract electrons towards himself.

PolarityWhat does polar mean?

What does non-polar mean?

A positive end and a negative endDifferent ends of the molecule have different chargesA dipole

No dipoleNo overall charges on the molecule

Do now:

What do you understand the following words to mean?

Electronegativity?

Polar?

Non-polar?

Covalent bond?

How good an atom is at attracting electrons to itself

Has a dipoleHas a positive and negative end

δ+δ-Has no dipole

Has no positive and negative end

The sharing of electrons between two non-metal atoms

Polar and non-polar covalent bonds

O = Othe electrons spend equal amount of time near each O atom

OH H

the electrons spend more time near the O atom than the H atom

Two atoms that have the same or similar electronegativity share electrons evenly. This means the bond between them is non-polar.

Two atoms that have different electronegativity do not share electrons evenly. This means the bond between them is polar.

For example: in an O – H bond the electrons are not shared evenly. They spend more time near the oxygen atom as it is more electronegative.

δ+δ-

δ+

δ-

δ+

δ-

Polar and non-polar covalent bondsAtoms with different electronegativity do not share electrons evenly. This is called a polar covalent bond (it has a dipole).

The end that attracts electrons more is slightly negative (δ-). The end that does not attract electrons as much is slightly positive (δ+).

OH H

δ-

δ+

δ-

δ+

Cl P Cl

Cl

δ- δ+

SciPad pg 58 and 59

Symmetry

CCl4 CH3Br PCl3 CO2

Molecules are symmetrical if they have a mirror image through all bonds.For example:

symmetry no symmetry

symmetry

no symmetry

no symmetry symmetry

Draw the Lewis diagram of and then make the following molecules and decide if they are symmetrical

no symmetry

Lone Pairs

Non-bonding regions around the central atom are known as lone pairs of electrons. For example:

Draw Lewis diagrams of the following molecules to decide if the following molecules have lone pairs of electrons around the central atom

CH4 CH3Cl PCl3 OF2

no lone pairs

no lone pairs

lone pairs lone pairs

Do now:

How could you tell if a whole molecule is polar or non-polar?

Has an overall dipole

Has polar bonds

Has no symmetry

Has a lone pair of electrons on the central atom

Polarity of moleculesAs well as describing bonds as polar or non-polar we can describe molecules as polar or non-polar. This is called polarity.

Polar molecules:• Have polar bonds and are unsymmetrical so

the polar bonds do not cancel out so the molecule has an overall dipole.

Cl P Cl

Cl

H C H

F

H• Have a lone pair of electrons on the central atom, so the molecule has an overall dipole.

OR

Polarity of moleculesAs well as describing bonds as polar or non-polar we can describe molecules as polar or non-polar. This is called polarity.

Non-polar molecules:• Have polar bonds and are symmetrical so

the polar bonds cancel out so the molecule has no overall dipole. H C H

H

HS C S

O O

• Have non-polar bonds and no lone pair on the central atom so the molecule has no overall dipole.

OR

Polarity of molecules

SciPad pg 60

Is polar or non-polar?

Does it have a lone pair on the central atom?Does it have polar bonds?Do the polar bonds cancel because of symmetry?

NoYes

No

Polar

Does it have a lone pair on the central atom?Does it have polar bonds?Do the polar bonds cancel because of symmetry?

NoYes

Yes

Non-polarIs polar or non-polar?

2013 Exam Q1 (c)

What do we need to cover to explain polarity?

What polarity is (a dipole)Bond polarityShape/symmetry

2013 Exam Q1 (c)What grade would you give this answer? Why?

Achieved

2013 Exam Q1 (c)Student discusses shape then…

Answering Exam QuestionsUsing a writing frame can help with your answer.

• State or explain the shape• Explain what polarity is and what determines if a molecule is

polar or non-polar• State the polar bonds and explain why they are polar (difference

in electronegativity)• Discuss the symmetry of the molecule and lone pairs around the

central atom• State if the bond dipoles cancel or not due to these reasons• State the polarity

• If asked compare polarities of different molecules

2014 Exam Q1 (c)

Do now:

What factors determine if a compound is polar or non-polar?

Jot down some key words

Are these compounds polar or non-polar, why?

polar non-polar polar

Covalent molecular compounds

So far we have learnt to:• Draw Lewis diagrams of compounds• Determine their shape• Explain their shape• Determine their polarity• Explain their polarity

We can also:• Explain their melting and boiling point or their state• Explain their electrical conductivity

We need to:• Explain their solubility in water

Usually Q1 in exam

Usually Q2 in exam

Links to CHEM2.2

Solubility

When two liquids have the same polarity they are miscible.

Soluble in each otherForm one continuous layer

When two liquids have different polarities they are immiscible.

Not soluble in each otherForm two distinct layers

This solubility rule is commonly known as ‘like dissolves like’.

Solubility

We are going to test the solubility of 5 different substances in water. (pg 65 SciPad)

Lets figure out if the compounds we are going to test are polar or non-polar.

C OH

H

H

H

C OC

H

HH

H

H

H

C OC

OH

H

H

H

C

C

C

C

C

C

H

H

H

H

H HH

H

H

H

H H

methanol ethanol ethanoic acid

cyclohexane

Solubility

Once you have finished your solubility experiments, practise explaining what you have seen by completing the SciPad pg 66 and 67.