1.1 Atomic Structure

Question 1

define relative atomic mass

Answer 1

average mass of an element compared to 1/12th of the mass of a carbon-12 atom

Question 2

define first ionisation energy

Answer 2

amount of energy needed to remove one mole of electrons from a mole of atoms in the gaseous state

Question 3

Answer 3

D

Question 4

What is the electron configuration of V^2+ in the ground state

Answer 4

1S2 2S2 2P6 3S2 3P6 3d3
Get rid of the 4s orbital first before the 3d orbital

Question 5

Define mass number of an atom

Answer 5

Number of protons and neutrons in the nucleus of the atom

Question 6

Describe how molecules are ionised using Electrospray ionisation
b) give the equation of C when it reached the detector using Electrospray ionisation

Answer 6

Sample is dissolved in a volatile solvent
Injected through needle at high voltage
Each molecule gains a proton / H+
b) C + H+ -> CH+.

Question 7

Between Magnesium & Alimunium, which has the lowest ionisation energy

Answer 7

Aluminium
Outer electron is in 3p Subshell
It is higher in energy, from the nucleus hence it is easier to remove

Question 8

The first ionisation energies of the elements in Period 2 change as the atomic number increases.
Explain the pattern in the first ionisation energies of the elements from lithium to neon.

Answer 8

General trend
- 1st IE increases
- more protons, nuclear charge increases, so stronger attraction to outer electron
- all have same shielding

Deviation from berylium to boron
- Boron lower than berylium
- Outer electron in 2P subshell which is an orbital higher in energy compared to 2S subshell

Deviation from Nitrogen to oxygen
- Oxygen lower than nitrogen
- 2 electrons in 2P need to pair
- pairing causes repulsion

Question 9

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

Answer 9

(for electrospray ionisation)
- A high voltage is applied to a sample in a polar solvent
- the sample molecule, M, gains a proton forming MH+
OR
(for electron impact ionisation)
the sample is bombarded by high energy electrons
the sample molecule loses an electron forming M+

Question 10

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

Answer 10

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

Question 11

A sample of ethanedioic acid was treated with an excess of an unknown alcohol in the presence of a strong acid catalyst. The products of the reaction were separated and analysed in a time of flight (TOF) mass spectrometer. Two peaks
were observed at m / z = 104 and 118.
(a) Identify the species responsible for the two peaks.

Answer 11

[CH3OCOCOOH]+
[CH3OCOCOOCH3]+

Question 12

Outline how the TOF mass spectrometer is able to separate two
species, of two different masses, to give two peaks.

Answer 12

• Positive ions are accelerated by an electric field
• To a constant kinetic energy
• as all have same KE, those with lower masses move travel faster and arrive at the detector first

Question 13

How is ionisation in electron impact done

Answer 13

high energy electrons
fired from electron gun
fired at sample
knocks off one electron

Question 14

Why is a negative charged plate used

Answer 14

positive ions are attracted to negative charged plate

Question 15

Explain how this current is generated.
b) Write an equation for the reaction that occurs when a tellurium ion hits the detector.

Answer 15

Electrons transferred from the detector To the positive ion
b) Te^+ + e^- -> Te

Question 16

The mass spectrum of tellurium also has a small peak at m / z = 64
Explain the existence of this peak.

Answer 16

2+ Ions formed / 2 electrons removed
From 128Te