A level Chem 1.1 Atomic Structure

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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)

Br₂(g) + e⁻ → Br₂⁺(g) + 2e⁻ (1)

State how the detector enables the relative abundance of each ion to be determined(1)

The (relative) abundance is proportional to the size of the current. (1)

Tellurium has a relative atomic mass of 127.6 Iodine has a relative atomic mass of 126.9 Define relative atomic mass. Suggest one property of tellurium that justifies its position before iodine in the modern Periodic Table. (3) 

Definition : Average mass of one atom of an element / 1/12 mass of one atom of carbon 12 (2)

Property- Te has one fewer proton than I (1)

Tellurium has several other isotopes. Two of these isotopes are 126Te and 124Te A different sample of tellurium is analysed using a TOF mass spectrometer. Which statement about kinetic energy (KE) is correct?

The KE of 126Te+ is the same as the KE of 124Te+

The table below shows some successive ionisation energies for an element in Period 3

Identify the Period 3 element. Explain your answer.

sulfur/ S (1) 

large difference between ionisation energy 6 and 7 (1)

electron removed from the second shell which is closer to the nucleus (1) 

State how the ions are detected, and how the abundance of each ion is measured, in a TOF mass spectrometer.(2)

(ions hit a detector and) each ion gains an electron (generating a current) (1)

(the abundance is) proportional to (the size of) the current (1) 

State the meaning of the term electron impact ionisation.

(High energy) electrons (from an electron gun) are used to knock out an electron (from each molecule or atom.) (1)

Define the term relative atomic mass

average/mean mass of 1 atom (of an element) /1/12 mass of one atom of 12C

The relative atomic mass of a sample of rhenium is 186.3 The table below shows information about the two isotopes of rhenium in this sample

Calculate the relative isotopic mass of the other rhenium isotope. Show your working.

(185×10) +( X x 17) /27 =187.1 (2)

State how the relative abundance of 185Re+ is determined in a TOF mass spectrometer. (2)

at the detector/(negative) plate the ions/Re+ gain an electron (1)

(relative) abundance depends on the size of the current(1)

Define relative molecular mass (1)

average mass of one molecule x 12 /mass of a 12C (1) 

State the equation that links number of particles, no. of moles and avogardro’s constant (1)

N=nL (1) 

State the equation that links the mass of one ion, relative isotopic mass and avogardro’s constant

mass of an ion(kg) = relative isotopic mass x 10^-3 / 6.022 x10²³ (1)

What are four factors that affect the size of Ionisation energy?(4)

• size of nuclear charge (1)

• distance of outer electrons from the nucleus (1)

• shielding effect of inner electrons (1)

• Spin-pair repulsion (1)

What is spin-pair repulsion ? (1)

It is the repulsive force experienced between two electrons when they’re forced to occupy the same atomic model. (1)

What happens to IE across a period ? (1)

IE increases (1)

What happens to IE down a group? (1)

IE decreases (1)

State the equation in electron impact (1) 

X(g) → X⁺(g) + e⁻ (1)

State the equation in electrospray ionisation (1)

X(g)+H⁺ → XH⁺(g) (1)

Name four stages of mass spectrometry (4)

• Ionisation (1)

• Acceleration (1)

• Ion drift (1)

• Detection (1)