Atomic Structure (AQA AS Chemistry): Exam Questions

Atoms are made up of three subatomic particles; protons, neutrons and electrons. 

Table 1 below shows data about these particles.

Table 1

Use the data from Table 1, and the Periodic Table, to calculate the mass of one atom of carbon in kg. 

¹²C, ¹³C and ¹⁴C are all isotopes of carbon.

State the difference between these three isotopes in terms of subatomic particles. 

A student claims that the different isotopes of carbon will have different chemical properties. 

Is the student correct? Explain your answer. 

Table 2 shown below contains data on the relative isotopic abundance of a chemical element, E. 

Table 2

i) Complete Table 2 by calculating ‘X’.

ii) Use the data from Table 2 to calculate the relative atomic mass, A_r, to 1 decimal place and use the Periodic Table to identify the element, E. 

A and B are different chemical elements, from different groups in the Periodic Table.

Explain why ^mA and ⁿA have identical chemical properties, but ^mA and ^pB have different chemical properties. 

An atom has twice as many protons, and twice as many neutrons, as an atom of 19F. Determine the chemical symbol for this atom, including the mass number, and deduce the number of electrons.

Elements exist as a mixture of isotopes.

i) Name an instrument which would be used to measure the relative abundances of isotopes of an element. 

ii) Explain the graph which would be produced, and how that graph and the data obtained would be used to calculate the relative atomic mass of the element in question. 

Helium has been found to react with sodium and form a stable compound.

This discovery by scientists was very unexpected. Explain why.

This question is about atomic structure. 

Write the full electron configuration for Ca and Ca²⁺.

All elements have a value for a first ionisation energy. 

i) Define the term first ionisation energy of an element. 

ii) Write the equation for the first ionisation energy of calcium.

Table 1 below gives the successive ionisation energies of a Period 3 element. 

Table 1

Identify the element, justifying your choice.

Explain why the value of the first ionisation energy of calcium is higher than that of potassium.

TOF (time of flight) mass spectrometry is a powerful instrumental method of analysis. 

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

In a TOF (time of flight) mass spectrometer, the ions formed are accelerated, detected and their abundance is determined. Explain how these three steps occur. 

An element, Z, has 4 isotopes, ⁸²Z, ⁸³Z, ⁸⁴Z and ⁸⁶Z.

i) Write an equation, including state symbols, to show how an atom of element Z is ionised by electron impact.

ii) Give the m/z value of the ion that would reach the detector first.

In a TOF mass spectrometer, the time of flight, t, of an ion is shown by the equation

Where d is the length of the flight tube in metres, m is the mass of an ion in kg and KE is the kinetic energy of the ions in the mass spectrometer. 

The time of flight of a ⁸²Z⁺ ion is 1.243 × 10⁻⁵ s

KE of an ion in the flight tube is 1.029 × 10⁻¹⁵ J

The Avogadro constant, L, is 6.022 x 10²³ mol^-1 

Calculate the time of flight of the ⁸⁴Z⁺ ion.

The Bohr model of an atom represents a central nucleus, consisting of protons and neutrons, with electrons surrounding it moving in circular orbits. This model was proposed by Niels Bohr in 1913 and after some further research, energy levels and sublevels were recognised, and the model was refined.  

Using your knowledge of atomic structure, complete Table 1 below for the particles found in an atom. 

Table 1

State the block in the Periodic Table in which silicon is placed and explain your answer.

A mass spectrometer can be used to detect isotopes of an element, such as silicon. For these to be detected in the mass spectrometer, a sample containing the isotopes must first be vapourised and then ionised.

State the sample must be ionised.

The graph below in Figure 1 shows the mass spectrum of a sample of silicon.

i) Using Figure 1, calculate the relative atomic mass, Ar, of this sample of silicon to 1 decimal place. 

ii) Suggest why the relative atomic mass on the Periodic Table might be different to the relative atomic mass of a sample analysed using a mass spectrometer. 

Successive ionisation energies provide the evidence for the arrangement of electrons in atoms. In Table 1, the successive ionisation energies of oxygen are given.

Table 1

i) Give the equation, including state symbols for the third ionisation energy of oxygen.

ii) Explain how this data shows evidence of two energy shells in oxygen.

Give the full electron configuration of the following atoms and ions.

i) Tellurium, Te

ii) Zinc(II) ion, Zn²⁺ 

iii) Copper(I) ion, Cu²⁺ 

Chlorine has two naturally occurring isotopes. ³⁵Cl with a mass of 34.969 and ³⁷Cl with a mass of 36.966. The relative atomic mass of Cl is 35.5. Calculate the abundance of each isotope to 2 d.p.

In order to ionise the sample of chlorine atoms in the Time of Flight (TOF) mass spectrometer, the sample must be ionised. 

i) Suggest why electron bombardment would be a more suitable method for a sample of chlorine, rather than electrospray ionisation. 

ii) Predict whether the atomic radius of ³⁵Cl or ³⁷Cl would be the greatest and give a reason for your answer. 

A sample of Cerium, Ce, was analysed in a Time of Flight (TOF) mass spectrometer. The relative abundances of three of the four main isotopes that were identified are shown in Table 1. 

A sample of Cerium, Ce, has four isotopes that have a known relative abundance. This sample has an Ar of 140.12.

Table 1

Use the data from Table 1 to calculate m, the mass number and the abundance of isotope ^mCe. 

A time of flight (TOF) mass spectrum for a sample of Cerium, Ce, was obtained. The sample analysed was ionised by electron impact. Identify the ion of Cerium, Ce, in Table 1 with the shortest time of flight and justify your answer.

An ⁸⁶Sr⁺ ion travels through the TOF mass spectrometer with a kinetic energy of 1.921 x 10^-15 J. 

The ion takes 1.09 x 10^-5 s to reach the detector. 

Calculate the length of the flight tube in meters. Give your answer to 3 significant figures.

    KE = mv²     v =    L = 6.02 x 10²³

A ⁷⁹Se⁺ ion travels through the flight tube with an energy of 6.27 x 10^-16 J.

Calculate the velocity of the ion.

A sample of element Z was extracted from a meteorite. Table 1 shows the relative abundance of each isotope in a mass spectrum of this sample of Z. Calculate the relative atomic mass of Z and suggest an identity of Z. Give your answer to 1 d.p. 

Table 1

TOF (time of flight) mass spectrometry is a powerful instrumental method of analysis. In order to obtain a mass spectrum of Z, a gaseous sample must first be ionised. Describe how ionisation takes place and give two reasons why ionisation is necessary. Include an equation to show the process of ionisation.

Sometimes in the mass spectrum on Z a very small peak with an m/z value of 32 is present. Explain the occurrence of this peak.

Calculate the mass of a single ⁶⁸Z⁺ ion in kg. Assume the mass of the ⁶⁸Z⁺ is the same as the ⁶⁸Z atom. Give your answer to 3 significant figures.

(The Avogadro Constant L = 6.02 x 10²³)

Amorphous, unorganised solid form, boron is used as a rocket fuel igniter and in pyrotechnic flares.

i) Write an equation, including state symbols to show the process that occurs when the first ionisation of boron, B, is measured. 

ii) Suggest why the ionisation energy of boron is lower than that of beryllium going against the general trend in ionisation energies across the period.

A naturally occurring sample of the element boron, B, has two isotopes and a relative atomic mass of 10.8.

i) Give the definition of relative isotopic mass.

ii) Calculate the relative abundances of both isotopes in the sample of boron, B.

Ions of boron, B, are deflected in a TOF mass spectrometer. Give one reason why isotopes of the same mass and velocity are deflected by different amounts in the same magnetic field.

A sample of another group three element Aluminum, Al, is analysed in a TOF mass spectrometer. The ²⁷Al⁺ ion travelled down a 5 m flight tube with a kinetic energy of 1.45 x 10^-13 J.

    KE = mv²     v =    L = 6.02 x 10²³

i) Calculate the mass of 1 aluminium atom in kg.

ii) Calculate the velocity of the Al+ ion travelling through the flight tube and give your answer to 3 significant figures.

iii) Calculate its time of flight and give your answer to 3 significant figures. 

Give the full electron configuration of the Cu⁺ ion. 

A sample of copper atoms were placed through a TOF mass spectrometer. Two isotopes of copper were detected, one of them being ⁶³Cu and the other being ⁶⁵Cu.

Calculate the velocity of the ⁶³Cu if it travels down a 5 m flight tube in 4.200 x 10^-6 s. Give your answer to 3 significant figures.

Calculate the percentage relative abundance of ⁶³Cu with a mass of 62.9296 and ⁶⁵Cu with a mass of 64.9278, when the average mass of the Cu isotope is 63.546. Give your answer to 3 significant figures.

Palladium is another transition metal that is primarily used in a catalytic converter in cars. 

i) Give the electron configuration for the Zirconium 2+ ion, Zr²⁺, starting with [Kr]. 

ii) Give the equation including state symbols to represent the third ionisation energy of Zirconium, Zr.