Topic 2 - Bonding and Structure

Question 1

what is ionic bonding?

Answer 1

the strong electrostatic attraction between oppositely charged ions

Question 2

what is covalent bonding?

Answer 2

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

Question 3

what is metallic bonding?

Answer 3

the strong electrostatic attraction between the lattice of metal cations and the sea of delocalised electrons

Question 4

what is a dative covalent bond?

Answer 4

when the shared pair of electrons come from the same atom

Question 5

what is the shape/angle of a molecule with 3 bonding pairs and 0 lone pairs?

Answer 5

trigonal planar, 120`

Question 6

what is the shape/angle of a molecule with 2 bonding pairs and 1 lone pair?

Answer 6

bent/v-shape, 118

Question 7

what is the shape/angle of a molecule with 4 bonding pairs and 0 lone pairs?

Answer 7

tetrahedral, 109.5

Question 8

what is the shape/angle of a molecule with 2 bonding pairs and 2 lone pairs?

Answer 8

bent, 104.5

Question 9

what is the shape/angle of a molecule with 5 bonding pairs and 0 lone pairs?

Answer 9

trigonal bipyramidal, 120 and 90

Question 10

what is the shape/angle of a molecule with 6 bonding pairs and 0 lone pairs?

Answer 10

octahedral, 90

Question 11

what is the shape/angle of a molecule with 2 bonding pairs and 0 lone pairs?

Answer 11

linear, 180

Question 12

compare the sizes of anions, cations and atoms of the same element

Answer 12

the negative ion is bigger than the atom - more electrons for the attraction to be distributed, weaker pull

the positive ion is smaller - stronger attraction because less electrons, greater pull

Question 13

what are the physical properties of ionic compounds?

Answer 13

• high melting points
• non conductor of electricity when solid
• conductor of electricity when molten/aqueous
• brittle

Question 14

why do ionic compounds have high melting points?

Answer 14

the giant lattice has very strong electrostatic forces between oppositely charged ions

Question 15

why do ionic compounds not conduct electricity as a solid?

Answer 15

ions are fixed in a lattice, and cannot move to carry charge

Question 16

why do ionic compounds only conduct electricity when molten/aqueous?

Answer 16

ions are free to move and carry charge

Question 17

why are ionic compounds brittle?

Answer 17

when ionic compounds are hit (e.g. hammer) it brings ions of the same charge next to each other, and the repulsive forces cause it to shatter

Question 18

why does electronegativity decrease down a group?

Answer 18

a shell is added, shielding the outermost electrons from the nucleus, making it harder for the nucleus to attract electrons

Question 19

why do giant atomic structures like diamond and graphite have high melting points?

Answer 19

there are lots of strong covalent bonds that take a lot of energy to break

Question 20

what determines if a molecule is polar?

Answer 20

presence of polar bonds (electronegativity difference) and asymmetry

Question 21

what are London forces?

Answer 21

induced dipole-dipole interactions, they are present in all molecular substances apart from ionic.

Question 22

how are London forces caused?

Answer 22

they are caused by the random/constant movement of electrons. this creates temporary dipoles in neighbouring molecules.

Question 23

how does electron number affect the size of London forces?

Answer 23

the more electrons there are, the higher chance that they will form temporary dipoles. this makes the London forces stronger.

Question 24

how does the shape of the molecule affect the size of London forces?

Answer 24

long straight alkanes have a large surface area of contact between molecules for London forces to form, compared to branched alkanes.

Question 25

where are permanent dipole-dipole forces present?

Answer 25

they occur between polar molecules due to the permanent imbalance of charge

Question 26

what is hydrogen bonding?

Answer 26

when hydrogen is bonded to an atom more electronegative to it

Question 27

what three atoms are more electronegative than hydrogen?

Answer 27

nitrogen, oxygen and fluorine

Question 28

how do ionic substances dissolve in water?

Answer 28

the bonds in the ionic lattice are broken, and new bonds are formed between the metal ions and the water molecules

Question 29

what is the requirement for a solute to dissolve in a solvent?

Answer 29

the energy required to break the solute/solvent bonds has to be equal to the energy given out to make new bonds between them

Question 30

why are larger alcohols less soluble in water?

Answer 30

the hydroxyl group is what is able to form hydrogen bonds with water. however, once the hydrocarbon chain increases, the hydroxyl group becomes less significant.

Question 31

what are the three factors affecting the strength of metallic bonding?

Answer 31

1. number of protons - the more protons, the stronger the bond 2. number of delocalised electrons - the more electrons the stronger the bond 3. size of ion - smaller ion, the stronger the bond

Question 32

why do metals have high melting points?

Answer 32

the electrostatic attraction between positive ions and delocalised electrons require a lot of energy to break

Question 33

why are metal malleable?

Answer 33

the planes of ions in the lattice can easily slide over each other

Question 34

what type of structure is NaCl?

Answer 34

giant ionic lattice

Question 35

what type of structure is diamond?

Answer 35

giant covalent lattice

Question 36

what type of structure is graphite?

Answer 36

giant covalent lattice

Question 37

what type of structure is magnesium?

Answer 37

giant metallic lattice

Question 38

why can diamond not conduct electricity?

Answer 38

there are already 4 electrons per carbon atoms, which means they are localised and cannot move.

Question 39

why can graphite conduct electricity well?

Answer 39

there are delocalised electrons between layers that can carry charge (not from one layer to another)