Atomic Structure

Question 1

Why does aluminium deviate from the I.E trend?

Answer 1

The outer electron is in a 3p orbital which is of a slightly higher energy than the 3s orbital. It therefore needs less energy to remove it

Question 2

Why does sulfur deviate from the I.E trend

Answer 2

One of the 3p orbital must contain two electrons . The repulsion between these paired electrons make it easier to remove them

Question 3

What is the general trend for I.E down a group?

Answer 3

General decrease

Because the outer electron is in a main level that gets further from the nucleus in each case

Question 4

Across period 2 which elements deviate from the ionisation trend?

Answer 4

Aluminium and sulfur

Question 5

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

Answer 5

(electronspray ionisation)

1. A high voltage is applied to a sample in a polar solvent
2. the sample molecule, M, gains a proton forming MH+

(for electron impact ionisation)

1. the sample is bombarded by high energy electrons
2. the sample molecule loses an electron forming M+

Question 6

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

Answer 6

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

Question 7

Explain how the electron pair repulsion theory can be used to deduce the shape of,
and the bond angle in, PF3

Answer 7

Stage 1: electrons round P
• P has 5 electrons in the outside shell
• With 3 electrons from 3 fluorine, there are a total
of 8 electrons in outside shell
• so 3 bond pairs, 1 non-bond pair
Stage 2: Electron pair repulsion theory
• Electron pairs repel as far as possible
• Lone pair repels more than bonding pairs
Stage 3: Conclusions
• Therefore, tetrahedral / trigonal pyramidal shape
• With angle of 109(.5)° decreased to 107°