1g - Covalent bonding

Question 1

What is the definition of a covalent bond?

Answer 1

Bond between Non-Metal and Non-Metal involving a shared pair of Electron between the two atoms in order to fill the outer shell, resulting in a strong attraction between the shared pair of Electrons and the Nuclei of the atoms involved.

Question 2

What are covalent bonds in terms of electrostatic attractions?

Answer 2

a strong attraction between a shared pair of electrons and two nuclei.

Question 3

What is a simple molecular structure?

Answer 3

Molecules with atoms joined by strong covalent bonds

Question 4

What are intermolecular forces of attraction?

Answer 4

Forces of attraction between molecules

Question 5

What is the melting point like with simple molecular structure?

Answer 5

Low melting and boiling point as they have weak intermolecular forces of attraction between Molecules, hence only small amounts of heat energy is needed to overcome forces and break down bonds. During the change of the state the covalent bonds within each molecule remain unbroken.

Question 6

Why do larger molecules tend to have a high melting and boiling point?

Answer 6

This is because larger molecules (molecules with more mass) have more forces of attraction between them. These forces, although weak, must be overcome if the substance is to boil, and larger molecules have more attractions which must be overcome.

Question 7

Do covalent compounds conduct electricity?

Answer 7

Electric current is a flow of charged particles that can move.

Covalent compounds do not conduct electricity.

Question 8

why do substances with giant covalent structures which are solids have high melting and boiling points?

Answer 8

they have a high melting point because it is a giant covalent structure with many strong covalent bonds that require a lot of energy to break.

Question 9

Explain why sodium bromide has a higher melting point then hydrogen bromide:

Answer 9

• NaBr has ionic bonding
• HBr has weak intermolecular forces
• ionic bonding is stronger

Question 10

What is a giant covalent structure?

Answer 10

Contains many Non-Metal atoms joined to adjacent atoms by Covalent Bonds, forming a Giant Lattice Structure

Question 11

Explain How the Structures of Diamond Influence their Physical properties Including Electrical Conductivity and Hardness: What are some uses?

Answer 11

1. HARD
   - Each Carbon atom is joined to four other Carbon atom to form a Giant Covalent Structure
   - Strong covalent bonds are difficult to break
2. HIGH MELTING POINT (SUBLIMATES)
   - Giant Covalent Structure so there are many strong covalent bonds that need to be broken down
   - Large amounts of heat energy is therefore needed to overcome forces and break down bonds
3. DOES NOT CONDUCT ELECTRICITY
   - All four valence Electrons are used in covalent bonds so there are no delocalised Electrons that are mobile to conduct electricity

USES:

• Cutting Tools
• Jewellery

Question 12

Explain How the Structures of Graphite Influence their Physical properties Including Electrical Conductivity and Hardness and what are some uses:

Answer 12

1. SOFT AND SLIPPERY
   - Forces of attraction between layers are weak so layers can easily slide over one another and be separated
2. HIGH MELTING (SUBLIMATES)
   - Giant Covalent Structure so there are many strong covalent bonds that needs to be broken down
   - Large Amounts of heat energy is needed to overcome forces and break down bonds
3. CONDUCTS ELECTRICITY
   - Only three valence Electrons are used in forming covalent bonds
   - Fourth Electron is delocalised and free to move between layers to conduct an electric charge

USES:

• Lubricant
• Electrodes for Electrolysis

Question 13

Explain How the Structures of C60 FULLERENE Influence their Physical properties Including Electrical Conductivity and Hardness and what are some uses:

Answer 13

1. SOFT
   - Each Carbon atom is joined to only three other Carbon atoms so has weak intermolecular forces of attraction between molecules
   - Bonds can be broken down easily making it soft
2. LOW MELTING AND BOILING POINT
   - Each Carbon atom is joined to only three other Carbon atoms so has weak intermolecular forces of attraction between molecules
   - Hence, only small amounts of heat energy is needed to overcome forces and break down bonds
3. CONDUCTS ELECTRICITY
   - Only three valence Electrons are used in forming covalent bonds
   - Fourth electron is delocalised and free to move to conduct an electric charge

USES:

• Drug Delivery System in the Body (Nanotubes)
• Lubricant
• Catalyst

Question 14

What are allotropes?

Answer 14

Allotropes are different forms of the same element. Three different allotropes of carbon are shown here as examples: diamond, graphite and C60 fullerene.

Question 15

Explain why carbon dioxide has a low melting and boiling point.

Answer 15

Carbon dioxide (CO2) has a simple molecular structure. This just means that it is made up of molecules.

Within each molecule are atoms bonded to each other covalently. These covalent bonds inside the molecules are strong.

However, between the molecules are weak forces of attraction that require little energy to break. These forces are not covalent bonds. This is why simple molecular substances such as carbon dioxide have a low boiling point.

Question 16

Why is carbon dioxide still made of carbon dioxide molecules after changing state?

Answer 16

So when carbon dioxide changes from a solid to a gas, for example, that process can be represented as:

CO₂ (s) → CO₂ (g)

Notice that even though there has been a dramatic change of state from solid to gas, the substance before and after the change is always made up of carbon dioxide molecules. During the change of the state the covalent bonds within each molecule remain unbroken. Instead it is the weak forces of attraction between the molecules which have been overcome.