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AQA Chemistry > Bonding & Structure: Covalent Bonding > Flashcards

Bonding & Structure: Covalent Bonding Flashcards

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1
Q

What is a covalent bond?

A

A shared pair of electrons between two atoms.

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2
Q

What properties do simple molecular covalent substances have?

A
  • do not conduct electricity
  • low melting and boiling points
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3
Q

What is a simple covalent molecule in terms of its structure?

A
  • contain only a few molecules (<100 atoms)
  • held together by covalent bonds
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4
Q

Why do simple covalent molecules not conduct electricity?

A

They do not have any free electrons or ions.

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5
Q

Why do simple covalent molecules have low melting and boiling points?

A

Little energy is needed to overcome the weak intermolecular forces

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6
Q

What is strong in a simple covalent molecule, what is weak?

A
  • strong covalent bonds between atoms
  • weak intermolecular forces between molecules
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7
Q

How do intermolecular forces change as the mass/size of the molecule increases?

A

They increase

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8
Q

What do stronger intermolecular forces mean for a substance‘s melting and boiling points?

A
  • increases melting and boiling points
  • more energy needed to overcome these forces
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9
Q

What are giant covalent substances?

A

Atoms covalently bonded in a giant lattice (regular repeated structure)

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10
Q

What properties do giant covalent substances have?

A
  • high melting and boiling points
  • most dont conduct electricity (dont normally have delocalised e-
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11
Q

Why do giant covalent substances have high melting and boiling points?

A

They have strong covalent bonds which require a lot of energy to overcome.

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12
Q

What are some allotropes of carbon?

A
  • diamond
  • graphite
  • fullerenes
  • nanotubes
  • graphene
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13
Q

What is an allotrope?

A

Different forms of an element that are bonded differently

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14
Q

Describe the structure of diamond.

A
  • each carbon atom is joined to 4 other carbon atoms by strong covalent bonds
  • the carbon atoms form a regular tetrahedral structure
  • no delocalised electrons
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15
Q

Why is diamond very hard?

A

It has strong covalent bonds.

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16
Q

Why does diamond have a very high melting and boiling point?

A

It has strong covalent bonds.

17
Q

Why is diamond not a conductor of electricity?

A

It has no delocalised electrons - all are involved in bonding

18
Q

What properties does diamond have?

A
  • very hard
  • very high melting point
  • not a conductor of electricity
19
Q

Describe the structure of graphite.

A
  • 3 covalent bonds per carbon atom
  • layers of hexagonal rings
  • weak forces of attraction between layers
20
Q

What properties does graphite have?

A
  • slippery, makes a good lubricant
  • conductor of electricity
  • softer than diamond
21
Q

Why is graphite slippery?

A

Layers can slide due to weak intermolecular forces

22
Q

Why is graphite soft?

A

The intermolecular forces of attraction between layers are weak

23
Q

Why can graphite conduct electricity?

A

Only bonded to 3 other carbons so one delocalised electron per carbon atom which can carry a charge through the structure.

24
Q

Describe the structure and properties of silicon dioxide.

A
  • SiO2: made up of silicon and oxygen
  • has the same structure and properties as diamond
25
Q

What are fullerenes?

A
  • hollow tubes or balls
  • made of carbon atoms
26
Q

What are the properties of fullerenes?

A
  • very strong
  • conduct electricity
27
Q

What are nanotubes?

A

Cylindrical fullerene with high length to diameter ratio

28
Q

What properties do nanotubes have?

A
  • high tensile strength
  • conductive
29
Q

Why can nanotubes conduct electricity?

A

Have delocalised electrons

30
Q

Why do nanotubes have a high tensile strength?

A

strong covalent bonds

31
Q

What is graphene in terms of structure?

A

a single layer of graphite

32
Q

What are some properties of graphene?

A
  • strong (strong bonds)
  • high melting point (strong bonds)
  • good conductor of electricity (delocalised electrons)
  • flexible
33
Q

Why do metals have high melting and boiling points?

A

Strong forces of attraction that require more energy toovercome

34
Q

What is a covalent bond between?

A

2 non-metals

AQA Chemistry (29 decks)

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