3.8 Covalent Bonding

Question 1

What type of atoms are held together by covalent bonds?

Answer 1

Non-metals

Question 2

What type of compounds does covalent bonding happen in?

Answer 2

Non-metal compounds

Question 3

Why are covalent bonds so strong?

Answer 3

The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces

Question 4

What does each singe covalent bond provide?

Answer 4

One extra shared electron for each atom

Question 5

What does having a full outer shell give non-metals?

Answer 5

The electronic structure of a noble gas, which is very stable

Question 6

Covalent bonds are directional. What does this mean>

Answer 6

The electron shells overlap in a particular direction

Question 7

Dot and cross diagrams (2)

Answer 7

• Electrons drawn in the overlap between the outer shells of two atoms are shared between those atoms.
• Dot and cross diagrams are useful for showing which atoms the electrons in a covalent bond come from, but they don’t show the relative sizes of the atoms, or how the atoms are arranged in space.

Question 8

Displayed formulas

Answer 8

• Displayed formulas show the covalent bonds as single lines between atoms.
• This is a great way of showing how atoms are connected in large molecules. However, they don’t show the 3D structure of the molecule. or which atoms the electrons in the covalent bonds have come from.

Question 9

Dimensional ball and stick models

Answer 9

• Dimensional ball and stick models show the atoms, the covalent bonds and their arrangement in space next to each other. But 3D models can quickly get confusing for large molecules where there are lots of atoms to include. They also don’t show where the electrons in the bonds have come from, either. 3D models also suggest that there are gaps between the atoms, when in fact, this space is where the shared electrons are.

Question 10

What are simple molecular substances, like chlorine, water and methane?

Answer 10

They are small molecules in which the atoms in the molecule are joined by strong covalent bonds. But, between the individual molecules, there are only weak intermolecular forces (which are easily broken).

Question 11

What are two groups of large substances that covalent bonds can make?

Answer 11

• Polymers
• Giant covalent structures

Question 12

What are giant covalent structures?

Answer 12

Things like silicon dioxide, diamond and graphite, which can involve billions or trillions of atoms, arranged in a regular lattice.

Question 13

Why are ‘simple molecules’ easily separated from each other?

Answer 13

The forces of attraction between separate molecules are weak, even though the covalent bonds between each group of atoms are very strong

Question 14

Why do simple molecules have low melting and boiling points?

Answer 14

The intermolecular forces (forces between molecules) only require a small amount of energy to break, which means they’ll break at low temperatures.