The New Progress Tracker

The New Progress TrackerFor each section of the module you will be given a progress tracker booklet. This is designed to enable you to sign of when a section of the specification is complete or has been reviewed and to allow communication between you and your teachers about the best way to help you to progress.

Starter• Write a definition for the term

“Electronegativity”

• Which element has the greatest electonegativity on the periodic table?

• What do you think the term “Electropositivity” might mean?

Electronegativity•The ability or desire of a particular atom to

pull electrons towards it in a molecule

•Fluorine has the greatest electronegativity

•Electropositivity could be described as the ability to push electrons away in a molecule, but more realistically is its lack of ability to pull electrons towards it▫Why do you think this is?

Intermolecular Bonding

ObjectivesBe able to...•Define intermolecular bonding•Explain the link between intermolecular

bonding and melting and boiling points•Explain the importance of molecular

shapes in intermolecular bonding•Describe three different types of

intermolecular bonding and their comparative strengths

Specification...Where this comes from...

Can we explain this?

Comparing Boiling Points of the Noble Gases

Noble Gas Bpt/C No. of e-

He -269 2

Ne -246 10

Ar -186 18

Kr -152 36

Xe -107 54

Rn -62 86

Can we explain

this?

Can we explain this?

What about this?

Millard’s

Theory

What about this?

Millard’s

Theory

Intermolecular Forces•Van der Waals forces (instantaneous dipole-

induced dipole interactions) exist between all molecules whether polar or non polar

•They are:▫Weak intermolecular forces▫Caused by very small or instantaneous

dipoles in molecules , caused by the random movement of electrons within electron clouds

Induced Dipoles•Movement of electrons produces an

oscillating dipole (temporary) – this oscillating dipole induces a dipole in a neighbouring molecule which is induced onto further molecules – induced dipoles attract one another.

•As electrons are constantly moving, dipoles are always being created and destroyed, however the overall effect is constant and the atoms are attracted to each other.

Factors which affect the strength:•The greater the number of electrons in

each molecule•The larger the oscillating and induced

dipoles•The greater the attractive forces

between molecules•How well the molecules fit together in

3D space... Tetris theory!

Questions•Grades C-

D•Grades A-B

Permanent Dipole-Dipoles•What is a polar molecule?

▫(a molecule which atoms have significant differences in their electronegativity and a dipole is created)

•+ and - charges on polar molecules cause weak electrostatic forces of attraction between molecules E.g. in HCl(g) H-Cl….. H-Cl….. H-Cl

•Although they are weak forces they are still much greater then VdWaals

Hydrogen Bonding• Special type of permanent dipole – dipole

interaction

• Hydrogen bonding can only occur when Hydrogen is bonded covalently to Fluorine, Nitrogen, or Oxygen.

• Hydrogen has a high charge density as it is so small and F, N & O are highly electronegative.

• The bond is highly polarised• Molecules which have hydrogen bonding are

usually organic

Examples of H-Bonding

Effects of H-Bonding•Hydrogen bonding has a huge effect on

the properties of substances. They are soluble in water and have higher boiling and freezing points than non-polar of similar size.

•Why does ice float? ▫ (less dense than liquid water due to rigid

Hydrogen bonds which are relatively long, molecules held in an open lattice structure)

H-bonding and Ice•Ice has relatively high melting point, and

water a relatively high boiling point•Relatively strong H-bonds between H2O

molecules•Extra forces on top of VdWaals•The extra intermolecular forces from H-

bonds also explains high surface tension and viscosity in water

Exam Question•State and explain the overall trend in

boiling points for Group 6 Hydrides. Why is water’s boiling point higher than expected in comparison to the other group 6 hydrides?

[Total 5 marks]

Exam Answers1. Except for water there is an increase in

boiling point going down the group

2. The increase in the size/Mr and number of electrons…

3. Leads to an increase in VdWaals

4. More energy…

5. Is needed to break the hydrogen bonds between waster molecules

ObjectivesBe able to...•Define intermolecular bonding•Explain the link between intermolecular

bonding and melting and boiling points•Describe three different types of

intermolecular bonding and their comparative strengths

Three types of intermolecular bonding...•Instantaneous dipole-induced dipole

(otherwise known as Van der Waals)•Permanent dipole-induced dipole•Permanent dipole-Permanent dipole (of

which Hydrogen bonding is an extreme example)

Three types of intermolecular bonding...

Home Learning•Complete worksheet on Intermolecular

Bonding for next lesson.