EL - Covalent bonding

Question 1

What is covalent bonding?

Answer 1

When atoms share electrons with one another so they’ve got a full outer shell.

Question 2

What do covalent bonds do?

Answer 2

Hold atoms in molecules together.

Question 3

How are molecules formed?

Answer 3

When 2 or more atoms bond together, and are held together by covalent bonds.

Question 4

What doesn’t matter in a molecule?

Answer 4

Doesn’t matter if the atoms are the same or different.

Question 5

For a covalent bond to be maintained, what does there have to be a balance between?

Answer 5

The electrostatic attraction between the nuclei and the electrons and the repulsion between the positive nuclei.

Question 6

What does covalent bonding happen between?

Answer 6

2 non-metals.

Question 7

What are the typical properties of molecular substances?

Answer 7

Fairly low melting points and boiling points.
Don’t conduct electricity.
Usually insoluble in water (or only very slightly soluble).

Question 8

Why do molecular substances have fairly low melting and boiling points?

Answer 8

There is no giant structure that needs to be broken down.

Question 9

What state are molecular substance at standard temperature and pressure (usually)?

Answer 9

Usually liquids or gases.

Question 10

Why don’t molecular substances conduct electricity?

Answer 10

There are no charge carriers that are free to move.

Question 11

Why are molecular substances usually insoluble in water?

Answer 11

The polar water molecules are more attracted to each other than the molecular substance and so tend to leave it alone.

Question 12

What has to happen to melt or boil a simple molecular compound?

Answer 12

You only have to overcome the intermolecular forces between the molecules. These are weak compared to ionic or covalent bonds. You don’t need to overcome the much stronger covalent bonds that hold the atoms together in the molecule.

Question 13

What diagram can be used to show how electrons behave in covalent bonds?

Answer 13

Dot-and-cross diagrams.

Question 14

How are the bonded molecules drawn in a dot-and-cross diagram for to show covalent bonds?

Answer 14

Drawn with their outer atomic orbitals overlapping. The shared electrons that make up the covalent bond are drawn within the overlapping area.

Question 15

Which electrons are shown in dot-and-cross diagrams?

Answer 15

Electrons in the outer shells.

Question 16

How many electrons does the central atom end up with most of the time?

Answer 16

8 electrons in its outer shell - Good for the atom as it is a very stable arrangement.

Question 17

How many electrons do atoms share with each other?

Answer 17

Depends. Atoms don’t have to stick to forming single bonds (one pair), you can get atoms sharing multiple pairs of electrons (e.g. 2 or 3 - double or triple bonds).

Question 18

What is it called if a there is a bond containing two electron pairs?

Answer 18

A double bond.

Question 19

What is it called if a there is a bond containing three electron pairs?

Answer 19

A triple bond.

Question 20

How is a double bond formed?

Answer 20

If a there is a bond containing two electron pairs.

Question 21

How is a triple bond formed?

Answer 21

If a there is a bond containing three electron pairs.

Question 22

What is dative covalent bonding?

Answer 22

Where both electrons come from one atom.

Where one atom donates both electrons to a bond.

Question 23

What is a dative bond also called?

Answer 23

A coordinate bond.

Question 24

What are examples of molecules that contain dative bonds?

Answer 24

Carbon monoxide, CO.

Ammonium ion, NH4+.

Question 25

Why are some covalent compounds special cases - what doesn’t need to happen?

Answer 25

Not all atoms need 8 electrons in their outer shell to be happy - some have more, and some have less.

Question 26

What does it mean if some atoms use the d-orbitals to ‘expand the octet’?

Answer 26

Means they have more than 8 electrons in their outer shell.

Question 27

How do some atoms have more than 8 electrons in their outer shell?

Answer 27

In a few compounds, some atoms use the d orbitals to ‘expand the octet’.