2.2.6 Covalent Bonding

Question 1

Carbon is in G4, how many covalent bonds does it form? Give an example.

Answer 1

• 4 covalent bonds

Question 2

Nitrogen is in G5, how many covalent bonds does it form? Give an example.

Answer 2

• 3 covalent bonds

Question 3

Oxygen is in G6, how many covalent bonds does it form? Give an example.

Answer 3

• 2 covalent bonds

Question 4

Hydrogen is in G1, how many covalent bonds does it form? Give an example.

Answer 4

• 1 covalent bond

Question 5

What is happening in covalent bonding? How do you measure the strength of a bond? Why does this happen?

Answer 5

1. The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
2. This attraction overcomes the repulsion between two +ive nuclei
3. Electrons are shared not transferred as with ionic b.
   . Measure the strength using average bond enthalpy (endothermic positive value)
   -This happens so bonding atoms achieve a noble gas config.

Question 6

What is a single bond? How are they written? Compare this to ionic bonding.

Answer 6

Atoms are bonded by one shared pair of electrons - vs ionic = in all directions. Written as H-H, eg. - single line.

Question 7

What is one single covalent bond?

Answer 7

Each shared pair of electrons

Question 8

Both water and NH3 have lone pairs, what are they?

Answer 8

An outer shell pair of electrons that is not involved in chemical bonding, to give a concentrated region of negative charge around the atom.

Question 9

What is a multiple bond? How are they drawn?

Answer 9

1. A double bond: two pairs in the space where one usually is - O2, CO2. Drawn with two ‘-‘ instead of one.
2. A triple bond: three pairs in the space where one usually is - N2. Drawn with three ‘-‘ instead of one.

Question 10

What is average bond enthalpy?

Answer 10

A measure of the average energy of a bond, and therefore the energy needed to break it

Question 11

Why is average bond enthalpy shown as a positive value? What unit is this value?

Answer 11

KJ/Mol-1 is positive because it is an endothermic value that requires energy

Question 12

O–O and C–C are both double bonds, which has stronger bond enthalpy and why?

Answer 12

C–C does, because it is in G4 and O is in G6

Question 13

C-H and H-H are both single bonds, which has a higher enthalpy and why?

Answer 13

H-H does, because C is in G4 and H is a noble gas