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Copy - IB Chemistry > Covalent Bonding > Flashcards

Covalent Bonding Flashcards

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1
Q

covalent bond

A

electrostatic attraction between a pair of electrons and positively charged nuclei

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2
Q

How does covalent bonding come about?

A
  • 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
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3
Q

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

A

by forces of repulsion between two nuclei

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4
Q

octet rule

A

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

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5
Q

lone pairs

A

pairs of electrons no involved in forming the bond

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6
Q

bond length

A

measure of distance between two bonded nuclei

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7
Q

bond strength

A

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

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8
Q

short bonds are – bonds

A
  • strong
  • atomic radius increases down group
  • atoms form molecules with longer bonds
  • shared electron pair further from pull of nuclei so bond weaker
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9
Q

multiple bonds are — and — than single bonds

A
  • 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
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10
Q

structure of graphite

A
  • 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
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11
Q

electrical conductivity of graphite

A
  • good electrical conductor
  • contains one non-bonded delocalised electron per atom that gives electron mobility
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12
Q

thermal conductivity of graphite

A

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

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13
Q

appearance of graphite

A
  • non-lustrous
  • grey
  • crystalline solid
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14
Q

special properties of graphite

A
  • soft and slippery due to slippage of layers over each other
  • brittle
  • very high melting point
  • most stable allotrope of carbon
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15
Q

structure of diamond

A
  • each C atom is covalently bonded to four others
  • arranged in tetrahedral with bond angles 109.5
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16
Q

electrical conductivity of diamond

A
  • non-conductor
  • all electrons bonded therefore non-mobile
17
Q

thermal conductivity of diamond

A
  • very efficient thermal conductor
  • better than metals
18
Q

appearance of diamond

A
  • highly transparent
  • lustrous crystal
19
Q

special properties of diamond

A
  • hardest known natural substance
  • cannot be scratched by anything
  • brittle
  • very high melting point
20
Q

structure of fullerene (C60)

A
  • 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
21
Q

electrical conductivity of fullerene

A
  • semi conductor at normal temperature and pressure
  • some electron mobility
  • easily accepts electrons to form negative ions
22
Q

thermal conductivity of fullerene

A

very low thermal conductivity

23
Q

appearance of fullerene

A

yellow crystalline solid

24
Q

special properties of fullerene

A
  • soluble in benzene
  • very light and strong
  • reacts with K to make superconducting crystalline material
  • low melting point
25
Q

structure of graphene

A
  • 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
26
Q

electrical conductivity of graphene

A
  • very good electrical conductor
  • one delocalised electron per atom gives electron mobility across layers
27
Q

thermal conductivity of graphene

A
  • best known thermal conductor
  • better than diamond
28
Q

appearance of graphene

A

almsot completely transparent

29
Q

special properties of graphene

A
  • thinnest and strongest material to ever exist
  • very flexible
  • very high melting point
30
Q

structure of silicon

A
  • 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
31
Q

What is silicon dioxide also known as?

A

silica or quartz

32
Q

structure of silicon dioxide

A
  • forms giant structures based on tetrahedral arrangement
  • O forms bridges between S atoms
33
Q

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

A
  • strong
  • insoluble in water
  • high melting point
  • non-conductor

Copy - IB Chemistry (23 decks)

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