IAL Chemistry Topic 2

Question 1

Isotope

Answer 1

Isotopes are different atoms of the same element that have the same number of protons but a different number of neutrons

Question 2

Atomic number

Answer 2

Atomic number is the number of protons in the nucleus of an atom.

Question 3

Mass number

Answer 3

Mass number is the sum of the number of protons and the number of neutrons in the nucleus of an atom.

Question 4

Relative isotopic mass

Answer 4

Relative isotopic mass is the mass of an atom of a particular isotope relative to 1/12 mass of a carbon-12 atom.

Question 5

How does a mass spectrometer work?

Answer 5

Vaporise sample into gas → passes through ionisation chamber to make positive ions → pass through electric field which are accelerated → pass through the magnetic field which are deflected (different paths) → detected by the ion detector

Question 6

Electronic configuration

Answer 6

The electronic configuration of an atom of an element is the distribution of electrons among atomic orbitals.

Question 7

Ionisation energy

Answer 7

Ionisation energy is the energy required to remove one electron from each atom in one mole of gaseous atoms of the element.
Energy of electrons when removed - energy of electrons in the orbital

Question 8

Trend of ionisation energy

Answer 8

The more electrons removed, the less electron-electron repulsion so the ionisation energy increases.
- across a period there is an increase in the first ionisation energy (more protons)
- down a group the first ionisation energy decreases

Question 9

Electron-electron repulsion effect

Answer 9

raises the energy in the shell of the electrons to the value they would have if there was no repulsion between them –> lower ionisation energy

Question 10

Factors that affect the energy of an electron

Answer 10

• the orbital in which the electron exists
• nuclear charge of the atom (number of protons)
• repulsion experienced by the electron from the other electrons in the atoms (high energy orbital increases repulsion / doubly occupied orbital increases repulsion)
• increase repulsion causes decrease in ionisation energy

Question 11

Which group has the highest energy in s,p,d orbital?

Answer 11

s orbital: group 1 and 2
p orbital: group 2-8
d orbital: transition metals

Question 12

How to measure the atomic radius?

Answer 12

→ distance from the nucleus to the boundary of an electron cloud. (orbitals → definite edge)
→ distance between 2 nuclei and divide it by two

Question 13

Type of radius and their type of atoms

Answer 13

Covalent radius (two bonded atoms)
Van Der Waals’ radius (two non-bonded atoms)
Metallic radius (metal atoms)

Question 14

Trend of atomic radii across a group

Answer 14

Atomic radii decrease across a period.
Electrons are being added to the same energy level and protons are being added to the nucleus.
This resulted in an increased nuclear charge (as the number of protons increases) and therefore the attractive force between the nucleus and electrons increases.
This force counterbalances the increased electron-electron repulsion that would occur due to the additional electrons in the quantum shells.

Question 15

Trend of atomic radii down a group

Answer 15

Atomic radii increase down a group
The number of occupied quantum shells increases making atoms bigger

Question 16

Melting and boiling points of different structures

Answer 16

Elements with giant lattice structures have high melting and boeing points.
Elements with simple molecular structures have low melting and boiling points.
Metallic → high
Covalent lattice → very high
Covalent molecular → low

Question 17

Trend of first ionisation energy across a period

Answer 17

Increase in the first ionisation energy.
More protons are being added to the nuclei of the atoms. This results in an increase in nuclear charge.
The electrons in the outer energy levels will be more tightly held (decrease energy IN SHELL) and more difficult to remove.
The increase in nuclear charge is stronger than the increase in electron-electron repulsion. Thus, increased attraction, higher ionisation energy.

Question 18

Trend of first ionisation energy down a group

Answer 18

First ionisation energy decreases.
Electrons removed from the outer energy level are increasingly distant from the nucleus as a result of the additional quantum shell. The attraction of the positive nucleus is decreased and it becomes easier to remove.
The outer electrons experience increased repulsion from the inner electrons which leads to a decreased ionisation energy.

Question 19

First ionisation anomalies

Answer 19

1. First ionisation of boron is lower than that of beryllium. Although the nuclear charge of the boron atom is greater than that of the beryllium atom, the outer electron of boron has more energy as it is in a 2p orbital as opposed to the 2s orbital for beryllium.
2. First ionisation of oxygen is lower than that of nitrogen. Although the nuclear charge of the oxygen atom is greater than that of the nitrogen atom, the electron-electron repulsion decreases the first ionisation energy of oxygen atom.