5.3 Covalent bonding

Question 1

What is covalent bonding

Answer 1

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 2

Where does covalent bonding occur

Answer 2

non-metallic elements, eg. H2 and O2
Compounds of non-metallic elements, for example H2O and CO2
Polyatomic ions for example NH4+

Question 3

What units can form by covalent bonds

Answer 3

Small molecule - eg. H2
Giant covalent structure - eg. SiO2
Charged polyatomic ion - eg. NH4+

Question 4

What is a covalent bond

Answer 4

An overlap of atomic orbitals each containing one electron to give a shared pair of electrons
Attraction is LOCALISED

Question 5

How does a covalent bond , bond

Answer 5

The shared pair of electrons is attracted to the nuclei of both the bonding atoms
The bonding atoms often have outer shells with the same electron structure as the nearest noble gas

Question 6

What is a molecule

Answer 6

The smallest part of a covalent compound that can exist while retaining the chemical properties of the compound

Question 7

Difference between ionic and covalent bonding

Answer 7

In covalent bonding, electrons are shared but in ionic bonding, the electrons are transferred

Question 8

What does the displayed formula show

Answer 8

The relative positioning of atoms and the bonds between them as lines
Ione pairs can also be added - eg. in H2O

Question 9

What are Ione pairs

Answer 9

Paired electrons that are not shared

Question 10

How many bonds are formed by carbon

Answer 10

4

Question 11

How many bonds are formed by nitrogen

Answer 11

3

Question 12

How many bonds are formed by oxygen

Answer 12

2

Question 13

How many bonds are formed by hydrogen

Answer 13

1

Question 14

When can ‘expansion of the octet’ take place

Answer 14

Only from the n=3 shell when a d-sub shell becomes available for the expansion
Example is sulfur hexafluoride

Question 15

When does a multiple covalent bond exist

Answer 15

When two atoms share more than one pair of electrons

Question 16

Where is the attraction in a double covalent bond

Answer 16

Electrostatic attraction is between two shared pairs of electrons and the nuclei of the bonding atoms

Question 17

Where is the attraction in a triple covalent bond

Answer 17

Between three shared pairs of electrons and the nuclei of the bonding atoms

Question 18

What is a dative covalent / coordinate bond

Answer 18

A covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only
In a dative covalent bond, the shared electron pair was originally a lone pair of electrons on one of the bonded atoms

Question 19

Example of a dative covalent bond

Answer 19

Formation of ammonium from ammonia and H+

Ammonia molecule donates its lone pair of electrons to a H+ ion
Dative covalent bond in NH4+ shown by a bond with an arrowhead -> to show that the nitrogen atom provides both electrons to the covalent bond
In an NH4+ ion, all four bonds are equivalent and you cannot tell which is the dative covalent bond. The arrow for the bond just helps with accounting for all electrons

Question 20

What is Average bond enthalpy

Answer 20

Serves as a measurement of covalent bond strength

The larger the value of the average bond enthalpy, the stronger the covalent bond