Structure and Bonding (polarity and intermolecular forces)

Question 1

What is a polar molecule?

Answer 1

a molecule with a permanent dipole

Question 2

What is a dipole?

Answer 2

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

Question 3

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

Answer 3

• 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 4

What is electronegativity?

Answer 4

the ability of an atom to attract the electron pair

Question 5

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

Answer 5

The Pauling Scale

Question 6

What is the most electronegative element?

Answer 6

Flourine

Question 7

What is a permanent dipole?

Answer 7

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

Question 8

What is a requirement for a molecule to be polar?

Answer 8

It must have a permanent dipole

Question 9

When can a molecule with polar bonds not be polar?

Answer 9

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

Question 10

Are intermolecular forces or intramolecular forces stronger?

Answer 10

intramolecular forces

Question 11

What is an example of an intramolecular force?

Answer 11

a covalent bond

Question 12

What is an intermolecular force?

Answer 12

A force between molecules

Question 13

What are the three types of intermolecular forces?

Answer 13

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

Question 14

Which is the weakest intermolecular force?

Answer 14

London forces

Question 15

Which is the strongest intermolecular force?

Answer 15

Hydrogen bonds

Question 16

From what are London forces formed from?

Answer 16

From temporary dipoles

Question 17

How is a temporary dipole formed?

Answer 17

• 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 18

What is a temporary dipole?

Answer 18

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

Question 19

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

Answer 19

• 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 20

What is an induced dipole interaction?

Answer 20

• 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 21

What does the strength of London forces depend on?

Answer 21

• The number of electrons in a molecule

Question 22

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

Answer 22

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

Question 23

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

Answer 23

two permanently polar molecules

Question 24

What is a permanent dipole-dipole interaction?

Answer 24

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

Question 25

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

Answer 25

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

Question 26

What is a hydrogen bond?

Answer 26

• 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 27

Where are hydrogen bonds found?

Answer 27

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

Question 28

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

Answer 28

A strong permanent dipole-dipole interaction

Question 29

Why do hydrogen bonds form?

Answer 29

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