[7.3] periodic trends in bonding and structure

Question 1

what is metallic bonding?

Answer 1

the strong electrostatic force of attraction between cations and delocalised electrons

Question 2

what are the mobility of cations and delocalised electrons?

Answer 2

• cations are fixed in position, maintaining the structure and shape of the metal
• delocalised electrons are mobile and able to move through the structure

Question 3

what type of structure are the metal atoms held in?

Answer 3

in a metal structure, billions of metal atoms are held together by metallic bonding in a giant metallic lattice

Question 4

properties of most metals

Answer 4

1. strong metallic bonds (attraction between cations and delocalised electrons)
2. high electrical conductivity
3. high melting and boiling points

Question 5

how can metals conduct electricity in solid and liquid states?

Answer 5

delocalised electrons can move through the structure, carrying charge

Question 6

why do most metals have high melting and boiling points?

Answer 6

• high temperatures are necessary to provide the large amount of energy needed to overcome the strong electrostatic forces of attraction between the cations and electrons
• this strong attraction results in most metals having high melting and boiling points

Question 7

what is the solubility of metals?

Answer 7

metals do not dissolve
- any interaction between polar solvents and the charges in a metallic lattice would lead to a reaction, rather than dissolving

Question 8

what do non-metallic elements exist as?

Answer 8

simple covalently bonded molecules
- in solid state, these molecules form a simple molecular lattice structure held together by weak intermolecular forces
> these structures have low melting and boiling points

Question 9

what non-metal elements exist as giant covalent lattices instead?

Answer 9

boron, carbon, and silicon

Question 10

why do giant covalent lattices have high melting and boiling points?

Answer 10

• they have very strong covalent bonds
• high temperatures are necessary to provide the large quantity of energy needed to break the strong covalent bonds

Question 11

why are giant covalent lattices insoluble in almost all solvents?

Answer 11

the covalent bonds holding together the atoms in the lattice are too strong to be broken by interaction with solvents

Question 12

why can giant covalent lattices not conduct electricity (except for graphite and graphene)?

Answer 12

• in carbon (diamond) and silicon, all four outer-shell electrons are involved in covalent bonding, so none are available for conducting electricity
• there are no mobile delocalised electrons that are free to move through the structure and carry charge

Question 13

why can graphite and graphene conduct electricity?

Answer 13

only three electrons of the four outer-shell electrons are used in covalent bonding. the remaining electron is delocalised, which means electricity can be conducted

Question 14

what is the structure of graphite?

Answer 14

• it has parallel layers of hexagonally arranged carbon atoms
• giant covalent lattice

Question 15

what is the structure of graphene?

Answer 15

it is a single layer of graphite, composed of hexagonally arranged carbon atoms linked by strong covalent bonds

Question 16

describe the trend in melting points across periods 2 and 3 [3]

Answer 16

• melting point increases from group 1 to 14
• there is a sharp decrease in melting point between group 14 and group 15
• the melting points are comparatively low from group 15 to group 18

Question 17

why is there a sharp decrease in melting point from group 14 to 15?

Answer 17

this marks a change from giant to simple molecular structures
- giant structures have strong forces to overcome so have higher melting points
- simple molecular structures have weak forces to overcome, so have much lower melting points