2.2.2 Bonding and Structure (electronegativity, bond polarity and intermolecular forces)

Question 1

What is electronegativity?

Answer 1

the ability of an atom to attract the bonding electrons in a covalent bond towards itself

Question 2

What are the factors affecting electronegativity?

Answer 2

• nuclear charge
• atomic radius
• electron shielding

Question 3

If there is more nuclear charge, what happens to the electronegativity of a molecule?

Answer 3

it is more electronegative

Question 4

If there is a greater atomic radius, i.e. more distance, what happens to electronegativity?

Answer 4

more electronegative

Question 5

If there is more electron shielding, what happens to electronegativity?

Answer 5

less electronegative

Question 6

What happens to electronegativity along a period and down a group?

Answer 6

it increases along a period and decreases down a group

Question 7

What scale are the values of electronegativity measured on, that you need to know of?

Answer 7

The Pauling Scale

Question 8

What is a polar bond?

Answer 8

A bond that contains a permanent dipole

Question 9

What is a dipole?

Answer 9

where one side of the molecule has a slightly positive charge, and the other side of the molecule has a slightly negative charge

Question 10

What causes the build up of partial charge on one atom?

Answer 10

• in a bond between two unlike atoms, one atom will have a stronger attraction to the electron pair than the other
• this means that the electron pair will not be at the centre of the bond
• causing a build up of partial charge on one atom

Question 11

What is a polar molecule?

Answer 11

a molecule with a permanent dipole (that does not cancel out)

Question 12

What is the most electronegative element?

Answer 12

Flourine

Question 13

What is a permanent dipole?

Answer 13

regions of partial positive charge and regions of partial negative charge within the same molecule

Question 14

What is a requirement for a molecule to be polar?

Answer 14

It must have a permanent dipole

Question 15

When can a molecule with polar bonds not be polar?

Answer 15

if the bonds are arranged symmetrically about the centre, then the partial charges will be the same on each side of the molecule

Question 16

Why is CH4 a non-polar molecule?

Answer 16

As C and H have similar electronegativities

Question 17

Are intermolecular forces or intramolecular forces stronger?

Answer 17

intramolecular forces

Question 18

What is an example of an intramolecular force?

Answer 18

a covalent bond

Question 19

What is an intermolecular force?

Answer 19

A force between molecules

Question 20

What are the three types of intermolecular forces?

Answer 20

1. London forces
2. Permanent dipole-dipole interactions
3. Hydrogen bonds

Question 21

Which is the weakest intermolecular force?

Answer 21

London forces

Question 22

Which is the strongest intermolecular force?

Answer 22

Hydrogen bonds

Question 23

From what are London forces formed from?

Answer 23

From temporary dipoles

Question 24

How is a temporary dipole formed?

Answer 24

• the electron clouds around molecules are constantly in motion
• at one moment, all the electron density can be on one side of the molecule, and the next, it can be somewhere totally different

Question 25

What is a temporary dipole?

Answer 25

where there are partial charges in a molecule, but they change very rapidly

Question 26

If a molecule has a temporary dipole, what will its partial charges do to other molecules?

Answer 26

• its partial charges will exert a force on nearby molecules
• the partial charge on one molecule can push away the electrons in another, or attract them towards it

Question 27

What is an induced dipole interaction?

Answer 27

• where a temporary dipole will induce dipoles in nearby molecules
• once a dipole has been induced, it will be attracted to the initial dipole

Question 28

What does the strength of London forces depend on?

Answer 28

• The number of electrons in a molecule

Question 29

Why will molecules with lots of electrons have stronger London forces?

Answer 29

• as they will have larger fluctuations in electron density
• this leads to larger temporary dipoles and stronger dipole-dipole interactions

Question 30

What kind of molecules do permanent dipole-dipole interactions exist between?

Answer 30

two permanently polar molecules

Question 31

What is a permanent dipole-dipole interaction?

Answer 31

where the δ+ of one molecule will attract the δ- of another molecule

Question 32

Why are permanent dipole-dipole interactions only found between polar molecules?

Answer 32

as permanent dipole-dipole interactions are only possible in molecules that contain a permanent dipole

Question 33

What is a hydrogen bond?

Answer 33

• a very strong permanent dipole- permanent dipole force, that can be formed with some elements
• when these are strong enough to be considered a bond, it is called a hydrogen bond

Question 34

Where are hydrogen bonds found?

Answer 34

they are found when you have a hydrogen atom bonded to either, oxygen, nitrogen or fluorine

Question 35

What will the hydrogen atom form when bonded to either the oxygen, nitrogen or fluorine?

Answer 35

A strong permanent dipole-dipole interaction

Question 36

Why do hydrogen bonds form?

Answer 36

When hydrogen is bonded to an extremely electronegative element, it develops a strong δ+ charge.

Question 37

What are the two anomalous properties of water due to hydrogen bonding?

Answer 37

1. Relatively high melting and boiling points
2. Ice having a much lower density than liquid water

Question 38

Why does water have relatively high melting and boiling points?

Answer 38

Due to the strong hydrogen bonds that require a lot of energy to overcome

Question 39

Why does ice have a lower density than water?

Answer 39

• ice has an open lattice structure
• where the hydrogen bonds in ice hold the molecules in a rigid structure with lots of air gaps