M2 Electrons and Bonding

Question 1

Define a shell

Answer 1

A shell is an energy level. The further from the nucleus, the higher the energy level.

Question 2

Define an atomic orbital

Answer 2

An atomic orbital is a region around the nucleus that can hold up to 2 electrons, with opposite spins.

Question 3

What are the sub-shells?

Answer 3

A shell can contain different sub shells: s, p, d and f.

Question 4

Describe the s sub-shell

Answer 4

Number of orbitals: 1
Maximum electrons: 2
Orbital structure: sphere

Question 5

Describe the p sub-shell

Answer 5

Number of orbitals: 3
Maximum electrons: 6
Structure: 3d dumbbell shape

Question 6

Describe the d sub-shell

Answer 6

Number of orbitals: 5
Maximum electrons: 10

Question 7

Describe the f sub-shell

Answer 7

Number of orbitals: 7
Maximum electrons: 14

Question 8

Electron configuration of argon (18)

Answer 8

1s^2 2s^2 2p^6 3s^2 3p^6

Question 9

Rule with 3d and 4s

Answer 9

The highest energy level of the third shell overlaps with the lowest energy level of the fourth shell, therefore 4s is filled before 3d. But is written 3d before 4s
eg. Sc: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^1

Question 10

Describe the rules for filling orbitals

Answer 10

1. Electrons fill into sub-shells with the lowest energy first
2. Orbitals within a sub-shell will fill singly before pairing up
3. Paired electrons have opposite spin

Question 11

Define ionic bonding

Answer 11

Electrostatic attraction between positive and negative ions

Question 12

Describe the structure of ionic compounds

Answer 12

• Each ion attracts oppositely charged ions in all directions, resulting in a giant ionic lattice containing millions of ions.

Question 13

Describe the melting and boiling points of ionic compounds

Answer 13

• Nearly all solid at room temperature as there is not enough energy to overcome the strong forces of electrostatic attraction between oppositely charged ions.
• High temperatures are needed to provide a large amount of energy to overcome the strong electrostatic attraction between ions, therefore ionic compounds have high melting and boiling points.
• Melting and boiling points are higher for lattices containing ions with greater ionic charges, as there is a stronger force of attraction between ions. Size of ions also affects the force of electrostatic attraction.

Question 14

Describe the solubility of ionic compounds

Answer 14

• Many ionic compounds dissolve in polar solvents (such as water). Polar molecules break down the lattice and surround each ion in solution.
• In a compound made of ions with large charges, the ionic attraction may be too strong for water to break it down the lattice, so the compound is not soluble.
• The positive ions are attracted to the negative end of the water molecule, and the negative ions are attracted to the positive end of the water molecule.

Question 15

Are common salts of sodium, potassium and ammonium soluble?

Answer 15

Yes

Question 16

Are nitrates soluble?

Answer 16

Yes

Question 17

Are common carbonates and hydroxides soluble?

Answer 17

No, except sodium, potassium and ammonium ones

Question 18

Are common chlorides soluble?

Answer 18

Yes, except silver and lead chloride

Question 19

Are common sulfates soluble?

Answer 19

Yes, except lead, barium and calcium sulfate

Question 20

What does solubility depend on?

Answer 20

• Solubility requires the ionic lattice to be broken down and water molecules must attract and surround the ions.
• The solubility of an ionic compound in water therefore depends on the relative strengths of attractions within the giant ionic lattice, and the attractions between ions and water molecules.
• Attractions in the giant lattice have the greater effect, and solubility decreases as ionic charge increases.

Question 21

Describe the electrical conductivity of ionic compounds

Answer 21

• When solid, an ionic compound does not conduct electricity, but once melted or dissolved it does conduct electricity.
• In solid: the ions are fixed in the giant ionic lattice so there are no mobile charge carriers.
• In liquid: the solid ionic lattice breaks down and the ions are free to move as mobile charge carriers.

Question 22

Define a covalent bond

Answer 22

A covalent bond is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 23

What does covalent bonding occur in?

Answer 23

Non-metallic elements eg. H2
Compounds of non-metallic elements, eg. H2O
Polyatomic ions, eg. NH4 +

Question 24

What is single covalent bonding?

Answer 24

Two atoms share a pair of electrons

Question 25

What is multiple covalent bonding?

Answer 25

In a double bond, the electrostatic attraction is shared between two pairs of electrons and the nuclei of the bonding atoms

Question 26

What is dative covalent bonding?

Answer 26

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

Question 27

What is a triple covalent bond?

Answer 27

The electrostatic attraction is between three shared pairs of electrons and the nuclei of the bonding atoms.

Question 28

What is average bond enthalpy?

Answer 28

Average bond enthalpy serves as a measurement of covalent bond strength. The larger the value of average bond enthalpy, but the stronger the covalent bond.