Covalent substances: Two kinds Flashcards

1
Q

What are the two kinds of covalent substances?

A
  • Simple molecular substances.

- Giant covalent structures (macromolecules).

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2
Q

In simple molecular substances what do the atoms form?

A

Very strong covalent bonds to form small molecules of several atoms.

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3
Q

In simple molecular substances what are the forces of attraction like between the bonds?

A

Very weak forces of attraction (intermolecular forces).

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4
Q

What happens as a result of the very weak forces of attraction in simple molecular substances?

A

Very low melting and boiling points.

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5
Q

Why are the melting and boiling points very low in simple molecular substances?

A

Because the molecules are easily parted from each other.

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6
Q

When simple molecular substances melt or boil what happens?

A

The weak intermolecular forces get broken (not the strong covalent bonds).

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7
Q

What are most simple molecular substances at room temperature?

A

Gases or liquids (although they can be solids).

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8
Q

What do simple molecular substances not do?

A

Conduct electricity.

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9
Q

Why don’t the simple molecular substances conduct electricity?

A

Because there no ions so there is no electrical charge.

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10
Q

What are giant covalent substances?

A

Macromolecules.

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11
Q

What are giant covalent structures similar to?

A

Giant ionic structures (lattices) except that there are no charged ions.

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12
Q

In macromolecules, what do the atoms form?

A

Strong covalent bonds (they are all bonded to each other).

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13
Q

In macromolecules what does their strong covalent bonds mean?

A

That they have very high melting and boiling points.

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14
Q

What don’t macromolecules do?

A

Conduct electricity (not even when molten).

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15
Q

What macromolecule is an exception to the rule that they don’t conduct electricity?

A

Graphite.

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16
Q

What are the main examples of macromolecules?

A
  • Diamond.
  • Graphite.
  • Silicon dioxide (silica).
17
Q

What are the bonds like in diamond?

A

Each carbon atom forms four covalent bonds.

18
Q

What structure does diamond form its covalent bonds in?

A

A very rigid giant covalent structure.

19
Q

What does diamonds structure make it?

A

The hardest natural substance.

20
Q

What is diamond used for?

A

Drill tips.

21
Q

What does diamond look like?

A

Sparkly.

22
Q

What is silica?

A

What sand is made of.

23
Q

In silica what is each grain of sand?

A

One giant covalent structure of silicon and oxygen.

24
Q

What are the bonds like in graphite?

A

Each carbon atom only forms three covalent bonds.

25
Q

What does graphite’s bonds mean?

A

That it creates layers which are free to slide over each other, so graphite is soft and slippery.

26
Q

How are the layers in graphite held together?

A

So loosely that they can be rubbed off onto paper (which is how a pencil works).

27
Q

Why are the layers in graphite held so loosely?

A

Because there are weak intermolecular forces between the layers.

28
Q

What is graphite the only?

A

Non-metal which is a good conductor of heat and electricity.

29
Q

What does each carbon atom have in graphite which allows it to conduct heat and electricity?

A

One delocalised electron (free electron).