Covalent Bonds and properties

Question 1

covalent bond

Answer 1

electrostatic attraction between a pair of electrons and positively charged nuclei

Question 2

How does covalent bonding come about?

Answer 2

when two non-metals react together
each want to gain an electron
able to achieve this by sharing electron pair
shared pair of electrons concentrated in region between two nuclei and is attracted to both atoms

Question 3

How are the forces of attraction between the nuclei and shared electrons balanced?

Answer 3

by forces of repulsion between two nuclei

Question 4

structure of graphite

Answer 4

each C atom is covalently bonded to three others
forms hexagons in parallel layers with bond angles of 120
layers only held together by weak London dispersion forces so can slide over each other

Question 5

electrical conductivity of graphite

Answer 5

good electrical conductor
contains one non-bonded delocalised electron per atom that gives electron mobility

Question 6

thermal conductivity of graphite

Answer 6

not a good thermal conductor unless heat can be force to conduct in direction parallel to crystal layers

Question 7

appearance of graphite

Answer 7

non-lustrous
grey
crystalline solid

Question 8

special properties of graphite

Answer 8

soft and slippery due to slippage of layers over each other
brittle
very high melting point
most stable allotrope of carbon

Question 9

structure of diamond

Answer 9

each C atom is covalently bonded to four others
arranged in tetrahedral with bond angles 109.5

Question 10

electrical conductivity of diamond

Answer 10

non-conductor
all electrons bonded therefore non-mobile

Question 11

thermal conductivity of diamond

Answer 11

very efficient thermal conductor
better than metals

Question 12

appearance of diamond

Answer 12

highly transparent
lustrous crystal

Question 13

special properties of diamond

Answer 13

hardest known natural substance
cannot be scratched by anything
brittle
very high melting point

Question 14

structure of silicon

Answer 14

S has four valence shell electrons
S can be covalently bonded to four other S (tetrahedral) in elemental form
forms a giant lattice structure like diamond

Question 15

What is silicon dioxide also known as?

Answer 15

silica or quartz

Question 16

structure of silicon dioxide

Answer 16

forms giant structures based on tetrahedral arrangement
O forms bridges between S atoms

Question 17

What are the properties of silicon dioxide due to strong holding atoms within lattice?

Answer 17

strong
insoluble in water
high melting point
non-conductor

Question 18

properties of covalent bonds

Answer 18

Low boiling points and melting points.
Various colours.
Poor conductors of heat and electricity.
Brittle solids.