bonding

Question 1

define ionic bonding

Answer 1

the electrostatic attraction between positive and negative ions

Question 2

name two examples of common cations

Answer 2

metal ions
ammonium ions

Question 3

name two examples of common anions

Answer 3

non-metal ions
polyatomic ions

Question 4

describe the structure of an ionic compound

Answer 4

each ion attracts oppositely charged ions in all directions, so the result is a giant ionic lattice structure containing billions of ions.

Question 5

describe the properties of ionic compounds

Answer 5

• high melting and boiling points
• only conduct electricity when liquid or aqueous
• tend to dissolve in polar solvents such as water

Question 6

explain why ionic compounds have high melting/boiling points

Answer 6

the electrostatic attraction between oppositely charged ions is strong and therefore requires a large amount of energy to overcome, which can only be provided by high temperatures

Question 7

explain why ionic compounds only conduct electricity when liquid or aqueous

Answer 7

in a solid state the ions are in a fixed position and cannot move, so there are no mobile charge carriers
when liquid or aqueous the solid ionic lattice breaks down, meaning the ions are now free to move and carry charge

Question 8

explain why ionic compounds tend to dissolve in polar solvents

Answer 8

the dipoles on the water molecules can bind to oppositely charged ions and break them apart

Question 9

what does solubility depend on?

Answer 9

the relative strengths of the attractions within the giant ionic lattice and the attractions between ions and water molecules

Question 10

define covalent bonding

Answer 10

the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 11

what is a dative covalent bond?

Answer 11

a covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only. the shared electron pair was originally a lone pair.

Question 12

what is the difference between a single and a double covalent bond?

Answer 12

in a single covalent bond only one pair of electrons are shared (2), whereas in a double covalent bond two pairs of electrons are shared (4)

Question 13

define metallic bonding

Answer 13

the strong electrostatic attraction between positive ions (cations) and delocalised electrons

Question 14

how many electrons would be in a metallic bond with metals of a 2+ charge?

Answer 14

twice as many electrons as cations (each atom donated its outer shell electrons to the ‘shared pool’ of delocalised electrons)

Question 15

what are the properties of metals?

Answer 15

high melting/boiling points
high electrical conductivity
strong metallic bonds

Question 16

explain why most metals have high melting and boiling points

Answer 16

high temperatures are needed to provide the large amounts of energy required to overcome the strong electrostatic attraction between the cations and delocalised electrons

Question 17

what does the melting/boiling point depend on?

Answer 17

the strength of the bonds holding together the atoms in the lattice

Question 18

explain why metals have a high electrical conductivity in both solid and liquid states

Answer 18

they have delocalised electrons which can move throughout the structure and carry charge

Question 19

name the three elements that form a giant covalent lattice

Answer 19

boron, carbon, silicon (and silicon dioxide)

Question 20

what are the three allotropes of carbon?

Answer 20

diamond, graphite and graphene

Question 21

what are the properties of diamond?

Answer 21

tetrahedral structure
high melting/boiling point
does not conduct electricity, as all four outer shell electrons in each atom are involved in covalent bonding with other atoms (this makes diamond very strong)

Question 22

what are the properties of graphite?

Answer 22

high melting/boiling point
can conduct electricity
hexagonal layers bonded by weak London forces

Question 23

what is the difference between graphite and graphene?

Answer 23

graphene is one layer of graphite

Question 24

why can graphite/graphene conduct electricity?

Answer 24

only three electrons in the outer shell of each carbon atom are involved in covalent bonding, so the other electron is delocalised and can move, carrying charge

Question 25

describe the variation of melting point across periods 2/3 in terms of structure and bonding

Answer 25

the melting point increases from group 1 to 4, and then sharply decreases between groups 4 and 5. This marks the change from giant to simple molecular structures. simple molecular structures have lower melting points as the bonds between them are weaker, requiring less energy to overcome.