ASChemistryEdexcelExam Questions1. Physical Chemistry1.1 Atomic Structure

Atomic Structure (Edexcel AS Chemistry)

Exam Questions

57 mins16 questions
Easy
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1a
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Bromine exists as two stable isotopes. The two isotopes are represented by the symbols begin mathsize 14px style Br presubscript 35 presuperscript 79 end style and begin mathsize 14px style Br presubscript 35 presuperscript 81 end style.

Give one similarity and one difference between these two isotopes by referring to the number of particles in the nuclei of the two isotopes.

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1b3 marks

The relative abundance of the two isotopes in a sample cannot be found in a chemical test.

i)
Give the reason why, despite the difference in atomic structure, the isotopes have the same chemical reactions.

(1)

ii)
State how the relative abundance of the two isotopes can be found.

(2)

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1c2 marks

i)

Complete the electronic configuration of a bromine atom.
(1)
1s2 2s2 ...........................................................................................

ii)
What is the number of electrons in the fourth quantum shell of bromine?
(1)
  ☐ A 2
  ☐ B 7
  ☐ C 17
  ☐ D 18

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2a1 mark

This is a question about atoms, isotopes and ions.

Which of the following pairs of ions is isoelectronic?

  ☐ A N3– and Cl–
  ☐ B O2– and S2–
  ☐ C Na+ and K+
  ☐ D Na+ and Mg2+

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2b1 mark

Which is a correct definition of relative isotopic mass?

  ☐ A

the weighted mean mass of an atom of an element relative to one twelfth of the mass of an atom of the isotope carbon-12
  ☐ B

the mass of one atom of an isotope relative to one twelfth of the mass of an atom of the isotope carbon-12
  ☐ C

the weighted mean mass of an atom of an element relative to 12g of the isotope carbon-12
  ☐ D

the mass of one atom of an isotope relative to the mass of 12g of the isotope carbon-12

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2c
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The percentage composition of the two bromine isotopes in a sample is given in the table.

Isotope Relative isotopic mass Percentage abundance
bromine-79 78.918 50.52
bromine-81 80.916 49.48

Calculate the relative atomic mass of bromine in this sample.
Give your answer to two decimal places.

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3a1 mark

This question is about atoms, molecules and ions.

The numbers of subatomic particles in an straight O presuperscript 18 atom are

  ☐ A 8 protons, 10 neutrons and 8 electrons
  ☐ B 9 protons, 9 neutrons and 9 electrons
  ☐ C 10 protons, 8 neutrons and 10 electrons
  ☐ D 18 protons, 18 neutrons and 18 electrons

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3b1 mark

The mass spectrum of a sample of bromine molecules with approximately equal proportions of the 79Br and 81Br isotopes is

q1b-9cho-al-1-june-2019-qp-edexcel-a-level-chem

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3c1 mark

The total number of electrons in all the occupied p orbitals in a chloride ion, Cl– ,is

  ☐ A 5
  ☐ B 6
  ☐ C 12
  ☐ D 18

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3d1 mark

Which of these isoelectronic ions has the largest ionic radius?

  ☐ A N3-
  ☐ B O2-
  ☐ C Na+
  ☐ D Al3+

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1a4 marks

This question is about chlorine.

Chlorine has two isotopes with mass numbers 35 and 37.

i)
Complete the table to show the numbers of subatomic particles in a 35Cl atom and a 37Cl− ion.

(2)

Particle Protons Neutrons Electrons
35Cl atom      
37Cl− ion      

ii)
A sample of chlorine contained 75% of 35Cl and 25% of 37Cl.

Complete the mass spectrum to show the peaks you would expect for the molecular ion straight C l subscript 2 superscript plus from this sample of chlorine gas.

(2)

q1aii-9cho-al-3-oct-2021-edexcel-a-level-chem

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1b1 mark

Write the formula of potassium chlorate(V).

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1c2 marks

Write the equation for the first electron affinity of chlorine. Include state symbols.

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1d2 marks

The standard electrode potential for the chlorine / chloride ion half-cell is

1⁄2Cl2 (aq) + e− ⇌ Cl− (aq)   E subscript cell superscript ⦵ = +1.36 V

i)
Identify an oxidising agent from the Data Booklet that will convert chloride ions into chlorine under standard conditions.

(1)

ii)
Calculate the value of E subscript cell superscript ⦵ for the reaction in (d)(i).

(1)

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2a
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This question is about atoms, molecules and ions.

Lithium exists as two isotopes.

Complete the table to show the numbers of subatomic particles in a 6Li atom and a 7Li+ ion.

Particle Protons Neutrons Electrons
6Li      
7Li+      

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2b
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The mass spectrum of a diatomic molecule, X2, has peaks at the following m / z values for the X2+ ion:

32, 33, 34, 35, 36

Deduce the formulae of all the species responsible for each of the peaks in the mass spectrum of X2, identifying element X and showing clearly the isotopes present.

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2c3 marks

Complete the table to show the maximum number of electrons which can fill each region of an atom.

Region Maximum number of electrons
the 1s orbital  
the 2p subshell  
the third quantum shell  

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3a2 marks

This question is about isotopes.

State, in terms of subatomic particles, what is meant by the term isotopes.

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3b
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The element gallium has a relative atomic mass of 69.735 and only contains two isotopes.

A sample of gallium contained the isotope 69Ga, with a relative abundance of 63.25 %.

Calculate the mass number of the other isotope.
You must show all your working.

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4a7 marks

This question is about isotopes.

The table shows data for some isotopes of potassium.

Isotope Relative isotopic mass Abundance %
39K 38.9637 93.218
40K 39.9340 0.012
41K 40.9618 6.770

i)
State what is meant by the terms ‘relative isotopic mass’ and ‘relative atomic mass’.
(3)

ii)

State what is meant by the term ‘isotopes’. Illustrate your answer by referring to the isotopes of potassium.

(2)


iii)
Use the data in the table to calculate the relative atomic mass of potassium.
Give your answer to 4 significant figures.
(2)

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4b5 marks

The relative isotopic abundances of an element can be measured using a mass spectrometer.
A simplified and incompletely labelled diagram of a mass spectrometer is shown.

q4b-8cho-as-1-nov-2020-qp-edexcel-a-level-chem

i)
Name the feature of the mass spectrometer responsible for the behaviour of the ions in the region indicated by the arrow X.

(1)

ii)
Explain the three ion pathways, A, B and C, shown in the region indicated by the arrow X.

(3)

iii)
Give a reason why the mass spectrometer must be operated under vacuum.
(1)

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