Chapter 6 - Electronegativity and Intermolecular Forces

Question 1

Define electronegativity

Answer 1

The attraction of a bonded atom for the pair of electrons in a covalent bond

Question 2

Fill out the electronegativity differences
Covalent = _____
Polar covalent = _____
Ionic = _____

Answer 2

Covalent = 0
Polar covalent = 0-1.8
Ionic = higher than 1.8

Question 3

Define polar covalent bond

Answer 3

Where the electron pair is not shared equally between the two bonded atoms

Question 4

A bond will be nonpolar when…

Answer 4

• the bonded atoms are the same

- the bonded atoms have the same or similar electronegativity

Question 5

Define dipole in simple terms

Answer 5

Separation of opposite charges in a molecule where one region has a small positive charge and the other has a small negative charge

Question 6

What are the three types of dipoles?

Answer 6

1) permanent dipoles
2) instantaneous dipoles
3) induced dipoles

Question 8

Define permanent dipole

Answer 8

The dipole in a polar covalent bond

Question 9

What determines whether a molecule is polar or not? (two factors)

Answer 9

1. Must contain one or more polar bonds

2. The molecule must be asymmetrical so the dipole isn’t cancelled

Question 10

What elements can hydrogen from hydrogen bonds with?

Answer 10

Fluorine
oxygen
nitrogen

Question 11

What do you consider when comparing melting and boiling points of molecules? (3 things)

Answer 11

1. intermolecular forces
2. molecular mass
3. hydrogen bonds?

Question 12

Name three weak forces of attraction/intermolecular forces, in order of increasing strength

Answer 12

— London dispersion forces
— permanent – permanent dipole interactions
— Hydrogen bonds

Question 13

Name three strong forces of attraction/ not intermolecular forces

Answer 13

— ionic
— covalent
— metallic

Question 14

What properties or molecule the intermolecular forces influence/affect?

Answer 14

melting point
boiling point
solubility
vapour pressure

Question 15

What is the alternative name for London dispersion forces?

Answer 15

Temporary/instantaneous dipole induced dipole interactions

OR Induced dipole dipole interactions

Question 16

Does Van der waal’s forces include?

Answer 16

London forces and permanent interactions

Question 17

How do London forces arise? (3 detailed points)

Answer 17

—The random distribution of electrons in an atom/molecule causes one side of the molecule to become slightly more negatively charged and the other side. This is called an instantaneous dipole.
—The slightly more negative region of this particle repose electrons in a neighbouring particle creating an induced dipole/it polarises it
— This creates an attractive force between the negative and positive poles of the molecules

Question 18

What is and how does an instantaneous dipole arise?

Answer 18

When at a point in time the random shifting of electrons causes one side of a molecule to become more negatively charged than the other.

Question 19

What is an induced dipole and how does it arise?

Answer 19

The slightly more negative region in an instantaneous dipole repels electrons in the neighbouring molecule, polarising it and thus induces (creates) a dipole.

Question 20

What happens to the intermolecular forces and covalent bonds with a simple molecular lattice is broken apart during melting?

Answer 20

Intermolecular forces break

Covalent bonds don’t break

Question 21

Nonpolar simple molecular compounds tend to be what in polar solvents and why?

Answer 21

Insoluble because there is little interaction between the molecules in the lattice and the solvent molecules thus the molecule doesn’t dissolve

Question 22

Why do you simple molecular structures not conduct electricity?

Answer 22

No mobile charged particles so nothing to complete electric circuit

Question 23

Name a few anomalous properties of water

Answer 23

— Solid water/ice is less dense than liquid water
— Relatively high melting/boiling point
— High surface tension
— Low viscosity

Question 24

Why does water have a high melting and boiling point?

Answer 24

It has (as with all molecules) London forces BUT also has hydrogen bonds

Question 25

Why is solid ice (below 4°C) less dense than liquid water?

Answer 25

The orientation of hydrogen bonds means there is a limit to how close to molecules can get

Question 26

What do polar molecules have both of?

Answer 26

Induced dipole interactions AND permanent dipole dipole interactions

Question 27

Higher Mr/electron number effect in London forces?

Answer 27

Stronger London forces

Question 28

Polar compounds dissolved in ___ solvents.

Nonpolar compounds dissolved in ____ solvents.

Answer 28

Polar

nonpolar