Atomic Structure Exam Qs

A sample of bromine (Br₂) is analysed in a mass spectrometer. The sample is ionised using electron impact ionisation.

Give an equation, including state symbols, for the process that occurs during the ionisation of bromine (1)

Three possibilities: (diatomic molecule)

1. ⁷⁹Br-⁷⁹Br = 79+79= 158
   → Probability: 0.5 × 0.5 = 0.25

2. ⁷⁹Br-⁸¹Br or ⁸¹Br-⁷⁹Br = 81+81=160
   → Probability: (0.5 × 0.5) + (0.5 × 0.5) = 0.5

3. ⁸¹Br-⁸¹Br = 81+81= 192
   → Probability: 0.5 × 0.5 = 0.25

Define relative atomic mass (2)

(5)

subtract 1 for the mass of H⁺

State the meaning of the term electron impact ionisation (1)

(high energy) electrons are used to knock out an electron

Identify the ion formed from this mixture that reaches the detector last

Justify your answer (2)

State why the isotopes of rhenium have the same chemical properties (1)