Physical I - AS

Question 1

Explain why the third ionisation energy of magnesium is much higher than the
second ionisation energy of magnesium.

Answer 1

Electron is removed from 2p sub-shell.
The electron being removed is less shielded than 3s.

Question 2

What is electronegativity?

Answer 2

The ability for an atom to attract a pair of electrons.

Question 3

Suggest, in terms of the intermolecular forces for each compound, why CBr4 has a
higher boiling point than CHBr3

Answer 3

CBr4 has van der Waals’ forces between molecules.
CHBr3 has van der Waals’ forces and dipole-dipole intermolecular
forces.
The van der Waals’ between CBr4 molecules are stronger than the
dipole-dipole and van der Waals’ forces between CHBr3.

Question 4

Describe how ions are formed in a time of flight (TOF) mass spectrometer.

Answer 4

A high voltage is applied to the sample (in polar solvent)
Molecules lose an electron

Question 5

Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer.

Answer 5

Ions, not molecules, will interact with and be accelerated by an
electric field
Only ions will create a current when hitting the detector

Question 6

Explain why CF4 has a bond angle of 109.5°

Answer 6

Around carbon there are 4 bonding pairs of electrons
Therefore, these repel equally and spread as far apart as possible