Structure of the Atom

27 Grade 9 Integrated Science questions on Structure of the Atom, with worked marking schemes. 27 questions are available on this topic in full.

1. Question 1

   1 mark

   Element Q has an electron arrangement of 2, 8, 1. To which group of the periodic table does Q belong?

   A. Group VII

   B. Group I

   C. Group VIII

   D. Group II

   (1 mark)

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2. Question 2

   1 mark

   The mass number of an atom is the sum of

   A. neutrons and electrons

   B. protons and neutrons

   C. protons only

   D. protons and electrons

   (1 mark)

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3. Question 3

   5 marks

   An atom of an element has the symbol notation ¹⁹₉X.

   (a) State the number of protons, neutrons and electrons present in this atom. (3 marks)

   (b) Define the term mass number. (2 marks)

   (5 marks)

   Marking scheme

   (a) Protons = 9 (equal to the atomic number, the lower figure); Electrons = 9 (a neutral atom has equal protons and electrons); Neutrons = mass number − atomic number = 19 − 9 = 10. (b) Mass number is the total number of protons and neutrons (nucleons) present in the nucleus of an atom.

4. Question 4

   1 mark

   A neutral atom becomes a positively charged ion when it:

   A. Gains one or more electrons

   B. Loses one or more electrons

   C. Gains one or more protons

   D. Loses one or more neutrons

   (1 mark)

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5. Question 5

   1 mark

   Which of the following correctly compares the relative masses of the sub-atomic particles?

   A. A neutron is much lighter than an electron

   B. All three particles have equal mass

   C. A proton and a neutron have almost equal mass, while an electron is much lighter

   D. An electron is heavier than a proton

   (1 mark)

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6. Question 6

   1 mark

   The mass number of an atom is 23 and its atomic number is 11. How many neutrons does the atom contain?

   A. 12

   B. 34

   C. 23

   D. 11

   (1 mark)

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7. Question 7

   1 mark

   Protons have a

   A. no charge

   B. positive charge

   C. variable charge

   D. negative charge

   (1 mark)

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8. Question 8

   1 mark

   An atom of magnesium has 12 electrons arranged in energy levels. Using the arrangement 2, 8, 2, how many electrons are in its outermost energy level?

   A. 12

   B. 8

   C. 2

   D. 10

   (1 mark)

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9. Question 9

   4 marks

   Draw the electron arrangement of the following elements:

   (a) Sodium (atomic number 11)

   (b) Chlorine (atomic number 17)

   (4 marks)

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10. Question 10

    1 mark

    Elements in the same group of the periodic table have the same number of

    A. electrons in the outer shell

    B. protons in the nucleus

    C. neutrons in the nucleus

    D. total electrons

    (1 mark)

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11. Question 11

    3 marks

    A form of chlorine has a mass number of 35 and another form has a mass number of 37, but both have 17 protons.

    (a) What name is given to such atoms of the same element?

    (b) Explain why they still belong to the same element.

    (3 marks)

    Marking scheme

    (a) Isotopes (1 mark). (b) They have the same number of protons / same atomic number (1 mark), so they are atoms of the same element; they differ only in the number of neutrons / mass number (1 mark).

12. Question 12

    1 mark

    An element X has an atomic number of 8. How many protons are present in one atom of X?

    A. 6

    B. 2

    C. 8

    D. 16

    (1 mark)

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13. Question 13

    4 marks

    An element has an atomic number of 12 and a mass number of 24.

    Determine:

    (a) The number of protons

    (b) The number of neutrons

    (c) The number of electrons

    (d) The electron arrangement

    (4 marks)

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14. Question 14

    6 marks

    State three differences between a proton and an electron in terms of charge, mass and location in the atom.

    (6 marks)

    Marking scheme

    Charge: proton is positively charged (+1) while electron is negatively charged (-1) (1 mark each = 2). Mass: a proton has a relatively large mass (~1 unit) while an electron has a negligibly small mass (1 mark each = 2). Location: protons are found in the nucleus while electrons are found in energy levels/shells around the nucleus (1 mark each = 2).

15. Question 15

    1 mark

    The part of the atom that contains protons and neutrons is the

    A. electron shell

    B. nucleus

    C. valence shell

    D. orbit

    (1 mark)

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16. Question 16

    1 mark

    The atomic number of an element is equal to the number of

    A. electrons and neutrons

    B. protons

    C. protons and neutrons

    D. neutrons

    (1 mark)

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17. Question 17

    1 mark

    Which scientist is credited with discovering the electron?

    A. James Chadwick

    B. John Dalton

    C. J.J. Thomson

    D. Ernest Rutherford

    (1 mark)

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18. Question 18

    5 marks

    An atom of an element X has 17 protons and a mass number of 35.

    (a) State the number of electrons and the number of neutrons in atom X. (2 marks)

    (b) Draw the electron arrangement (energy level diagram) of atom X. (2 marks)

    (c) State the valency of element X. (1 mark)

    (5 marks)

    Marking scheme

    (a) Number of electrons = 17 (equal to the number of protons in a neutral atom). Number of neutrons = mass number - protons = 35 - 17 = 18 neutrons. (b) Electron arrangement: first energy level holds 2 electrons, second holds 8, third holds 7, i.e. 2,8,7 (a diagram showing three concentric shells around the nucleus with 2 electrons on the innermost, 8 on the middle and 7 on the outer shell). (c) Valency = 1, because the outer shell has 7 electrons and needs to gain 1 electron to attain a stable octet (8 electrons in the outer shell).

19. Question 19

    1 mark

    An atom has 11 protons and 12 neutrons. Its mass number is

    A. 12

    B. 23

    C. 11

    D. 1

    (1 mark)

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20. Question 20

    1 mark

    An atom is made up of three sub-atomic particles. These are

    A. neutrons, ions and electrons

    B. atoms, elements and compounds

    C. protons, neutrons and electrons

    D. protons, molecules and ions

    (1 mark)

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21. Question 21

    4 marks

    An atom of aluminium has an atomic number of 13 and a mass number of 27.

    (a) State the number of protons, neutrons and electrons in the atom.

    (b) Write down its electron arrangement.

    (4 marks)

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22. Question 22

    1 mark

    A learner is told that an atom of sodium has 11 protons, 12 neutrons and 11 electrons. Which particle in the atom carries no charge?

    A. Electron

    B. Neutron

    C. Proton

    D. Nucleus

    (1 mark)

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23. Question 23

    1 mark

    Electrons are arranged in energy levels (shells). The maximum number of electrons in the first shell is

    A. 32

    B. 2

    C. 8

    D. 18

    (1 mark)

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24. Question 24

    2 marks

    Define the following terms as used in the structure of the atom: (a) Atomic number (b) Mass number.

    (2 marks)

    Marking scheme

    (a) Atomic number = the number of protons in the nucleus of an atom (1 mark). (b) Mass number = the total number of protons and neutrons in the nucleus of an atom (1 mark).

25. Question 25

    5 marks

    During a science lesson, learners studied an atom of sodium with mass number 23 and atomic number 11.

    (a) State the number of protons, neutrons and electrons in this atom. (3 marks)

    (b) Explain why the atom as a whole is electrically neutral. (2 marks)

    (5 marks)

    Marking scheme

    (a) Protons = 11 (equal to the atomic number); Neutrons = mass number − atomic number = 23 − 11 = 12; Electrons = 11 (equal to the number of protons in a neutral atom). (3 marks: 1 each) (b) The atom is electrically neutral because the number of positively charged protons (11) is exactly equal to the number of negatively charged electrons (11), so the positive and negative charges cancel out / balance, leaving no overall charge. (2 marks)

26. Question 26

    1 mark

    During a lesson, a teacher draws a diagram showing a small dense central region of an atom containing protons and neutrons. What is this region called?

    A. Nucleus

    B. Electron shell

    C. Ion

    D. Energy level

    (1 mark)

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27. Question 27

    4 marks

    An atom of an element has a mass number of 23 and an atomic number of 11.

    (a) State the number of protons, neutrons and electrons in this atom. (3 marks)

    (b) State one difference between the mass number and the atomic number of an atom. (1 mark)

    (4 marks)

    Marking scheme

    (a) Protons = 11 (equal to the atomic number); Electrons = 11 (equal to the number of protons in a neutral atom); Neutrons = mass number - atomic number = 23 - 11 = 12. (b) The mass number is the total number of protons and neutrons in the nucleus, while the atomic number is the number of protons only (which also equals the number of electrons in a neutral atom).

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