Shapes Of Molecules And Intermolecular Forces 2.6.1

Question 1

Electron pair repulsion theory

Answer 1

-Electron pairs around the central atom repel each other as far apart as possible
-The greater the number of electron pairs, the smaller the bond angle
- Lone pairs of electrons repel more strongly than bonded pairs of electrons

Question 2

Linear

Answer 2

180• 2 bonded pairs with no lone pairs

Question 3

Trigonal planar

Answer 3

120• Three bonded pairs of electrons

Question 4

Tetrahedral

Answer 4

109.5• 4 bonding pairs of electrons

Question 5

Octahedral

Answer 5

90• 6 bonded pairs of electrons

Question 6

Pyramidal

Answer 6

107• 3 bonded pairs of electrons and one lone pair repelling more

Question 7

Non linear

Answer 7

104.5• 2 bonded pairs and two lone pairs repelling more

Question 8

Electronegativity

Answer 8

The ability of an atom of an element to attract electrons towards itself in a covalent bond

Question 9

How does electronegativity increase?

Answer 9

The further up and right you go in the periodic table (excluding noble gases) the more electronegative the element is.

Question 10

What are the most electronegative elements?

Answer 10

FONCL

Question 11

Electronegativity difference in purely covalent bonding?

Answer 11

0 (non-polar)

Question 12

Electronegativity difference in a polar covalent structure?

Answer 12

0 to 1.8

Question 13

Electronegativity difference in an ionic bonding?

Answer 13

Greater than 1.8, the bigger the difference in Electronegativity, the more ionic the compound will be.

Question 14

What leads to a polar molecule?

Answer 14

An uneven distribution of charge

Question 15

Factors that affect electronegativity

Answer 15

• Atomic radius
• Electron shielding
• Nuclear charge

Question 16

How does atomic radius affect electronegativity?

Answer 16

As the radius of an atom increases, the bonding pairs of electrons become further from the nucleus = less attracted to the positive charge of the nucleus =lower electronegativivity

Question 17

How does nuclear charge affect electronegativity?

Answer 17

The greater the number of protons in a nucleus, the greater the attraction to the electrons in a covalent bond = resulting in a higher electronegativity

Question 18

How does electron shielding affect electronegativity?

Answer 18

As electron shielding increases the electron shielding decreases, as the electrons are further away from the positively charged nucleus, lowers ability to pull in electrons, decreasing the electronegativity.

Question 19

How can a molecule be asymmetrical?

Answer 19

If the dipoles don’t cancel each other out then they are arranged asymmetrically - overall they are polar.

Question 20

Strength of intermolecular forces (Weakest to Strongest)

Answer 20

• London forces/ Induced dipole (non-polar)
• Permanent dipole-dipole interactions (polar)
• Hydrogen forces

Question 21

How do induced dipole forces arise?

Answer 21

• Electrons are constantly moving so the instantaneous dipole is constantly shifting
• The instantaneous dipole induces a dipole on a neighbouring molecule
• The induced dipole induces further dipoles on neighbouring molecules which then attract one another

Question 22

Permanent dipole-dipole interactions

Answer 22

Polar molecules have permanent dipoles, will always have a negatively and positively charged end, they are attracted to each other.

Question 23

Melting and boiling points of simple molecular substances

Answer 23

Have a low melting and boiling point- only the weak intermolecular forces break, the covalent bonds are strong and do not break

Question 24

Solubility of non polar simple molecular substances

Answer 24

Non polar solvent can dissolve non polar substance

Question 25

Solubility of polar solvent

Answer 25

A polar solvent can dissolve a polar solution

Question 26

Why does the London forces increase as you go down the group (group 7)

Answer 26

Increase in size = more electrons = more London forces being established = more energy required to over come the intermolecular forces

Question 27

What is hydrogen bonding formed between?

Answer 27

NOF (e.g water can form two hydrogen bonds because Oxygen has two lone pairs)

Question 28

What are the anomalous properties in water?

Answer 28

-High melting and boiling points
- High surface tension
- Density of ice compared to water

Question 29

Why does ice have a lower density than liquid water?

Answer 29

The hydrogen bonds are held together in an open lattice, holding the water molecules further apart, decreasing the density. However when ice melts the ice lattice collapses and the molecules are closer together, so liquid water is more dense

Question 30

Boiling point of water

Answer 30

Water has a high boiling point because they have hydrogen forces above the London forces, so a higher amount of energy is needed to overcome the hydrogen bonds in water.

Question 31

What lattice is iodine in and what forces are it held by?

Answer 31

Crystal lattice held by weak intermolecular forces. Because it is non polar, it is held together due to instantaneous induced dipole interactions (weakest) and sublimes.

Question 32

What vapour is released when iodine sublimes?

Answer 32

Purple vapour

Question 33

What can reduce the surface tension of water

Answer 33

Detergents

Question 34

Conductivity of covalent substances

Answer 34

Do not contain any freely moving charged particles- unable to conduct electricity in either the solid or liquid state however some polar covalent molecules can ionise and will conduct electricity.