Topic 2 - Bonding and Structure

Question 1

Ionic bond

Answer 1

the strong electrostatic attraction between oppositely charged ions

Question 2

Effect of ionic radius on the strength of ionic bonding

Answer 2

larger ions with larger ionic radii will have a weaker attraction to the oppositely charged ion because attractive forces have to act over a greater distance

Question 3

Effect of ionic charge on the strength of ionic bonding

Answer 3

Ions with a greater charge will have a greater attraction to the other ions, resulting in stronger forces of attraction and therefore stronger ionic bonding

Question 4

Trend in ionic radii down a group

Answer 4

As you go down each group, the ions have more electron shells. Therefore, ionic radius increases.

Question 5

Trend in ionic radii across a period

Answer 5

Ionic radius decreases as number of protons increases. Positive charge of the nucleus increases, so electrons are pulled closer to the nucleus.

Question 6

Evidence for the existence of ions

Answer 6

• conduct electricity
• during electrolysis, positive ions in solution are attracted to cathode and
  negative ions in solution are attracted to the anode
• physical properties: high MP, soluble in water but not in non-polar solvents

Question 7

Relationship between bond length and bond strength in covalent bonds

Answer 7

inversely proportional

As bond length decreases, the strength of the covalent bond increases, as electrons involved are more tightly held when the distance between the nuclei of the bonded atoms is smaller

Question 8

Covalent bond

Answer 8

the strong electrostatic attraction between two nuclei and the shared pair of electrons between them

Question 9

Order of repulsion in covalent bonds

Answer 9

lone pair – lone pair > lone pair – bond pair > bond pair – bond pair

Question 10

Linear structure bond angle

Answer 10

180˚

Question 11

Trigonal planar structure bond angle

Answer 11

120˚

Question 12

Bent structure bond angle

Answer 12

104.5˚

Question 13

Pyramidal structure bond angle

Answer 13

107˚

Question 14

Tetrahedral structure bond angle

Answer 14

109.5˚

Question 15

Trigonal bipyramidal structure bond angles

Answer 15

120˚
90˚

Question 16

Octahedral structure bond angle

Answer 16

90˚

Question 17

Electronegativity

Answer 17

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

Question 18

Electronegativity difference needed for ionic bonds

Answer 18

𝜟x > 1.7

Question 19

Electronegativity difference needed for polar covalent bonds

Answer 19

1.7 ≥ 𝜟x ≥ 0.5

Question 20

Electronegativity needed for pure covalent bonds

Answer 20

𝜟x < 0.5

Question 21

London force (instantaneous dipole – induced dipole)

Answer 21

a temporary attractive force due to the formation of temporary dipoles in a non-polar molecule

the constant “sloshing around” of the electrons in the molecule causes rapidly fluctuating dipoles

Question 22

Permanent dipoles

Answer 22

weak intermolecular forces of attraction that arise between permanently polar molecules

Occur when two atoms in a molecule have substantially different electronegativity: one atom attracts electrons more than the other, becoming more negative, while the other atom becomes more positive

Question 23

Hydrogen bond

Answer 23

a special type of permanent dipole-dipole force that forms when hydrogen forms a covalent bond with a very electronegative element: either nitrogen, oxygen or fluorine

Question 24

Why water has a high melting/boiling temperature

Answer 24

Hydrogen bonds are relatively strong. These extra forces in addition to London forces require more energy to be overcome

Question 25

Why ice is less dense than water

Answer 25

Open lattice structure in ice means rigid hydrogen bonds hold the water molecules apart (hydrogen bonds in ice are longer) When ice melts, hydrogen bonds collapse, allowing water molecules to come closer together

Question 26

Trend in boiling temperature of alkanes with increasing chain length

Answer 26

Boiling point increases as there are more points of contact with each adjacent molecule, causing stronger London forces between adjacent molecules

Question 27

Branching on boiling temperatures in alkanes

Answer 27

Branching makes molecules more compact, reducing surface area. Branched alkanes will have lower boiling points than straight chain alkanes.

Question 28

Why alcohols have a low volatility and higher BP compared to alkanes with a similar number of electrons

Answer 28

They possess hydrogen bonds in addition to London forces and dipole-dipole interactions, whereas alkanes only have London forces

Question 29

The trends in boiling temperatures of the hydrogen halides, HF to HI

Answer 29

HF > HI > HBr > HCl HF can form hydrogen bonds while the others can't Increase from HCl to HI is caused by increasing London forces due to increasing number of electrons

Question 30

Water dissolving ionic compounds

Answer 30

water can break down or disrupt the ionic lattice and surround each ion in solution the greater the ionic charge, the less soluble an ionic compound is

Question 31

Water dissolving simple alcohols

Answer 31

Alcohols have a hydroxyl group that can form hydrogen bonds with water alcohols with longer carbon chains show decreased solubility due to the hydrocarbon chain's non-polar character overruling the polar hydroxyl group

Question 32

Water as a poor solvent for halogenoalkanes

Answer 32

The dipole moment of halogenoalkanes is too weak to form hydrogen bonds with water molecules. The hydrogen bonds between water molecules are stronger than the dipole interactions that can form between water molecules and the halogenoalkane so the compound does not dissolve

Question 33

Like dissolves like

Answer 33

Compounds which have similar intermolecular forces to those in the solvent will generally dissolve e.g., non-polar solvents will dissolve non-polar solutes as London forces can form between them

Question 34

Metallic bonding

Answer 34

the strong electrostatic attraction between metal ions and the delocalised electrons

Question 35

In what are giant lattices present?

Answer 35

- ionic solids (giant ionic lattices) - covalently bonded solids, such as diamond, graphite and silicon(IV) oxide (giant covalent lattices) - solid metals (giant metallic lattices)

Question 36

Diamond structure

Answer 36

- a giant lattice of carbon atoms with strong bonds in all directions - each carbon is covalently bonded to four others in a tetrahedral arrangement with a bond angle of 109.5˚ - the hardest substance known for this reason it is used in drills and glass-cutting tools

Question 37

Graphite structure

Answer 37

- 3 bonds - trigonal planar - sheets of hexagons -> slippery, single electrons are delocalised and conduct electricity - strong/lightweight - insoluble

Question 38

Graphene structure

Answer 38

- a single layer of carbon atoms that are bonded together in a repeating pattern of hexagons - 3 covalent bonds per atom and the 4th outer electron per atom is delocalised

Question 39

Dative covalent bond

Answer 39

both electrons of the covalent bond come from one atom (arrow instead of dash) e.g., NH4+