Why does aluminium deviate from the I.E trend?
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
Why does sulfur deviate from the I.E trend
One of the 3p orbital must contain two electrons . The repulsion between these paired electrons make it easier to remove them
What is the general trend for I.E down a group?
General decrease
Because the outer electron is in a main level that gets further from the nucleus in each case
Across period 2 which elements deviate from the ionisation trend?
Aluminium and sulfur
Describe how ions are formed in a time of flight (TOF) mass spectrometer
(electronspray ionisation)
- A high voltage is applied to a sample in a polar solvent
- the sample molecule, M, gains a proton forming MH+
(for electron impact ionisation)
- the sample is bombarded by high energy electrons
- the sample molecule loses an electron forming M+
Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer.
- Ions, not molecules, will interact with and be accelerated by an electric field
- Only ions will create a current when hitting the detector
Explain how the electron pair repulsion theory can be used to deduce the shape of,
and the bond angle in, PF3
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°
