Covalent Bonding

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

octet rule

Answer 4

tendency of atoms to form a stable arrangement of eight electrons in their outer shell

Question 5

lone pairs

Answer 5

pairs of electrons no involved in forming the bond

Question 6

bond length

Answer 6

measure of distance between two bonded nuclei

Question 7

bond strength

Answer 7

measure of energy required to break bond (described in terms of bond enthalpy)

Question 8

short bonds are – bonds

Answer 8

• strong
• atomic radius increases down group
• atoms form molecules with longer bonds
• shared electron pair further from pull of nuclei so bond weaker

Question 9

multiple bonds are — and — than single bonds

Answer 9

• shorter and stronger
• greater number of shared electrons
• stronger force of electrostatic attraction between bonded nuclei
• greater pulling power of nuclei bringing them closer together

Question 10

structure of graphite

Answer 10

• 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 11

electrical conductivity of graphite

Answer 11

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

Question 12

thermal conductivity of graphite

Answer 12

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

Question 13

appearance of graphite

Answer 13

• non-lustrous
• grey
• crystalline solid

Question 14

special properties of graphite

Answer 14

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

Question 15

structure of diamond

Answer 15

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

Question 16

electrical conductivity of diamond

Answer 16

• non-conductor
• all electrons bonded therefore non-mobile

Question 17

thermal conductivity of diamond

Answer 17

• very efficient thermal conductor
• better than metals

Question 18

appearance of diamond

Answer 18

• highly transparent
• lustrous crystal

Question 19

special properties of diamond

Answer 19

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

Question 20

structure of fullerene (C60)

Answer 20

• bonded in sphere of 60 carbon atoms - consists of 12 pentagons and 20 hexagons
• closed spherical cage
• each carbon bonded to three others
• not a giant molecule because has fixed formula

Question 21

electrical conductivity of fullerene

Answer 21

• semi conductor at normal temperature and pressure
• some electron mobility
• easily accepts electrons to form negative ions

Question 22

thermal conductivity of fullerene

Answer 22

very low thermal conductivity

Question 23

appearance of fullerene

Answer 23

yellow crystalline solid

Question 24

special properties of fullerene

Answer 24

• soluble in benzene
• very light and strong
• reacts with K to make superconducting crystalline material
• low melting point

Question 25

structure of graphene

Answer 25

* each C atom covalently bonded to 3 others forms hexagons with bond angles 120 * single layers * exist as 2D material only * honeycomb or chicken wire structure

Question 26

electrical conductivity of graphene

Answer 26

* very good electrical conductor * one delocalised electron per atom gives electron mobility across layers

Question 27

thermal conductivity of graphene

Answer 27

* best known thermal conductor * better than diamond

Question 28

appearance of graphene

Answer 28

almsot completely transparent

Question 29

special properties of graphene

Answer 29

* thinnest and strongest material to ever exist * very flexible * very high melting point

Question 30

structure of silicon

Answer 30

* 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 31

What is silicon dioxide also known as?

Answer 31

silica or quartz

Question 32

structure of silicon dioxide

Answer 32

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

Question 33

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

Answer 33

* strong * insoluble in water * high melting point * non-conductor