Periodic Trend In Structure and Melting Point

Question 1

what is metallic bonding?

Answer 1

strong electrostatic attraction between cations and delocalised electrons

Question 2

what is the structure of all metals?

Answer 2

giant metallic lattice

Question 3

what are examples of giant covalent lattices?

Answer 3

• carbon (diamond, graphite and graphene)
• silicon

Question 4

what are solid covalent lattices?

Answer 4

networks of atoms bonded by strong covalent bonds to form giant covalent lattices

Question 5

what are the properties of metals?

Answer 5

• high melting and boiling point
• high electrical conductivity(able to conduct in solid and liquid states)
• insoluble

Question 6

why do metals have their properties?

Answer 6

• metallic bonding and the giant metallic lattice(high mp and bp)
• delocalised electrons(conductivity)

Question 7

what is the shape of a carbon(diamond) and silicon?

Answer 7

tetrahedral and bond angle 109.5

Question 8

what are the general properties of the giant covalent lattices?

Answer 8

• high melting and boiling points
• insoluble
• graphene and graphite being the only giant covalent structures to conduct electricity

Question 9

why do giant covalent lattices have a high melting and boiling point?

Answer 9

• giant covalent lattice
• strong covalent bonds between the atoms
• high amounts of energy needed to break these covalent bonds

Question 10

why are giant covalent lattices insoluble?

Answer 10

covalent bonds holding atoms together are too strong to be broken by interactions with any solvent

Question 11

why do giant covalent lattices like graphene and graphite conduct electricity?

Answer 11

• in graphene and graphite each carbon atom is bonded to 3 other carbon atoms
• so there is a delocalised electron to carry electrical charge around the structure

Question 12

why can’t carbon(diamond) and silicon conduct electricity?

Answer 12

• each bonding electron is covalently bonded to 4 other carbon atoms
• so there are no delocalised electrons to carry an electrical charge

Question 13

what is the trend in melting point across period 2 and period 3?

Answer 13

• melting point increases from groups 1-14(4)
• sharp decrease in melting point in group 15(5)
• melting points are low from group 15(5) to 18(0)

Question 14

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

Answer 14

change in structure from giant metallic/ionic lattices to simple molecules

Question 15

why do simple molecules have a low melting point?

Answer 15

• weak London forces, so less energy required to overcome these forces

Question 16

why do giant structures have a high melting point?

Answer 16

• strong electrostatic attractions which require a lot of energy to break

Question 17

where does the staircase begin, separating the giant molecules to the simple molecules?

Answer 17

under boron

Question 18

where does the melting point drop in period 2?

Answer 18

carbon to nitrogen

Question 19

where does the melting point drop in period 3?

Answer 19

silicon to phosphorus

Question 20

what are the changes in lattice across a period?

Answer 20

• giant metallic to giant covalent to simple molecular lattices