Chapter 7.1: covalent bonding

Question 1

What are covalent bonds?

Answer 1

Bonds formed by sharing electrons between atoms

Question 2

What are the 2 structures of covalent substances?

Answer 2

Simple molecular structure and giant molecular structure

Question 3

What are the physical properties of simple molecular structures?

Answer 3

1) Low melting and boiling points
Eg. Bromine, Br2

• Within each bromine molecule, bromine atoms are held together by strong intramolecular covalent bonds
• However, between bromine molecules, only weak intermolecular forces that are easy to overcome hold them together

2) Usually insoluble in water and soluble in organic solvents

3) Do not conduct electricity in any state
- No free-moving ions or electrons to conduct electricity

Question 4

What are the physical properties of giant molecular substances?

Answer 4

1) Very high melting/boiling points
- Large number of atoms held together by strong covalent bonds
- Large amount of heat energy needed to break these bonds

2) Do not conduct electricity (except graphite)
- All outer electrons are used to form covalent bonds
- No free electrons to move through structure and conduct electricity

3) Insoluble in water and organic solvents
- Held together in strong covalent bonds
- Forces of attraction between structure and solvent molecules are not strong enough to break the bonds

Question 5

How was diamond account for its physical properties?

Answer 5

1) Hard and high melting point
- Each carbon atoms covalently bonds with 4 other carbon atoms
- 3-dimensional giant molecular structure with strong covalent bonds
- Difficult to break

2) Does not conduct electricity
- All outer electrons of carbon atoms used for bonding
- No free electrons to move through structure to conduct electricity

Question 6

How does graphite account for its physical properties?

Answer 6

1) Graphite has high melting/boiling point
- Each carbon atom covalently bonds with 3 other carbon atoms to form a continuous layer of hexagons
- Difficult to break these strong covalent bonds

2) Soft and slippery
- Layers of carbon atoms are held loosely by weak intermolecular forces of attraction
- Can slide over each other when force is applied
- Intermolecular forces are easily broken

3) Conducts electricity
- Each carbon atom has one outer electron unused for covalent bonding
- Can move freely along layers from one carbon atom to the next
- Delocalised electrons allow graphite conduct electricity

Question 7

How does silicon dioxide account for its physical properties?

Answer 7

1) High melting and boiling point
- Each silicon atom is bonded to 4 oxygen atoms and each oxygen atom bonds with 2 silicon atoms
- Forms 3d structure with hard-to-break covalent bonds

2) Does not conduct electricity
- No free electrons to move through structure and conduct electricity