2.6 SHAPES OF MOLECULES AND INTERMOLECULAR FORCES

Question 1

What are molecules?

Answer 1

Molecules are two or more atoms bonded covalently

Question 2

What is the electron pair repulsion theory?

Answer 2

Electron pair repulsion theory:
-e and e both negative
-e pairs repel as far away as possible
-lone pairs repel greater than bonded pairs

lone and lone = greatest repulsion
lone and bonded = less repulsion
bonded and bonded = least repulsion

Question 3

What shape and angle is 2 bonded pairs?

Answer 3

2 bonded pairs = linear, 180

Question 4

What shape and angle is 3 bonded pairs?

Answer 4

3 bonded = triaganol planar, 120

Question 5

What shape and angle is 4 bonded pairs?

Answer 5

4 bonded = tetrahedral, 109.5

Question 6

What shape and angle is 5 bonded pairs?

Answer 6

5 bonded = triagonal bi-pyramidal, 90

Question 7

What shape and angle is 6 bonded pairs?

Answer 7

6 bonded = octahedral, 90

Question 8

What shape and angle is 2 bonded pairs and 2 lone pairs?

Answer 8

2 bonded 2 lone = non-linear, 104.5

Question 9

What shape and angle is 3 bonded pairs and 1 lone?

Answer 9

3 bonded 1 lone = pyramidal, 107

Question 10

What is polarity?

Answer 10

Molecules that have a separation of charge are polar. As nuclear charge increases, molecules become more polar

Question 11

What is electronegativity?

Answer 11

Electronegativity is the ability to attract electrons in a covalent bond.
Fluorine is the most electronegative, then oxygen, then nitrogen

Question 12

What does electronegativity depend on?

Answer 12

Electronegativity depends on:
1. nuclear charge
2. distance between outer electrons and nucleus
3. level of shielding by other electron shells

Question 13

What happens to electronegativity?

Answer 13

Electronegativity increases across a period as nuclear charge increases and decreases down a group as shielding increases.
Ionic bonding is the degree of separation (the degree of ability to attract electrons to itself)

Question 14

What are intermolecular forces?

Answer 14

Intermolecular forces are weak interactions between the dipoles of different molecules

Question 15

What are the types of intermolecular forces?

Answer 15

Types of intermolecular forces:
London forces = exist in all molecules, easily broken
permanent dipole-dipole interactions
hydrogen bonding

Question 16

What are dipoles?

Answer 16

Dipoles:
-created when electrons move towards more electronegative atoms
-separation of opposite charges
-in symmetrical molecules, dipoles cancel out
-permanent dipoles = occur between permanent delta negative and positive ends of molecules
-induced dipoles (London forces) = exist between all molecules

Question 17

How are London forces made?

Answer 17

London forces are made by:
1. random movement of electrons introduces and instantaneous dipole
2. this dipole will induce another dipole in a neighbouring molecule
3. induced dipole introduces more dipoles which attract one another

Question 18

What is hydrogen bonding?

Answer 18

Hydrogen bonding occurs between the hydrogen atom that is bonded to either nitrogen, oxygen or fluorine and another electronegative atom
-electronegativity of O, N, F atom pulls electron away from H atom which gives it a small positive charge- forms a hydrogen bond with one pair of electrons on N, O or F atom
-strongest and hardest to overcome