Atomic structure quiz: 25 questions with answers

Questions and answers

By CanQuiz

An AI wrote the questions in this quiz from its creator’s material. It may contain mistakes.

1. 1.Where in an atom are protons and neutrons found?

   • In the nucleus
   • In the electron shells
   • In the outermost electron shell only
   • Spread evenly through the whole atom
   Show answer

   Answer: In the nucleus

   Explanation: Protons and neutrons are packed together in the nucleus at the centre of the atom. Electrons occupy the shells around it.

2. 2.What is the relative charge of a neutron?

   • +2
   • +1
   • -1
   • 0
   Show answer

   Answer: 0

   Explanation: A neutron is electrically neutral, so its relative charge is 0. Protons carry +1 and electrons carry -1.

3. 3.Compared with a proton, roughly how heavy is an electron?

   • About 1/10 of a proton's mass
   • About 1/1840 of a proton's mass
   • About twice a proton's mass
   • About the same mass as a proton
   Show answer

   Answer: About 1/1840 of a proton's mass

   Explanation: An electron's mass is tiny: close to 1/1840 of a proton's, which is why it is often treated as almost zero when working out the mass of an atom.

4. 4.The atomic number of an element is equal to the number of which particles in its atoms?

   • Protons plus neutrons
   • Neutrons
   • Protons
   • Occupied electron shells
   Show answer

   Answer: Protons

   Explanation: The atomic number is the proton number. Every atom of a given element has the same number of protons, and that number fixes which element it is.

5. 5.Most of the mass of an atom is concentrated in its nucleus.

   • True
   • False
   Show answer

   Answer: True

   Explanation: Protons and neutrons, which are far heavier than electrons, are both in the nucleus. So nearly all of the atom's mass sits there, in a very small volume.

6. 6.A sodium atom has atomic number 11 and mass number 23. How many neutrons does it contain?

   • 34
   • 23
   • 11
   • 12
   Show answer

   Answer: 12

   Explanation: Neutrons = mass number minus atomic number, so 23 - 11 = 12.

7. 7.Two isotopes of the same element differ in their number of what?

   • Neutrons
   • Occupied electron shells
   • Protons
   • Electrons in the neutral atom
   Show answer

   Answer: Neutrons

   Explanation: Isotopes have the same number of protons (so they are the same element) but different numbers of neutrons, which gives them different mass numbers.

8. 8.What does the mass number of an atom tell you?

   • The total number of protons and electrons
   • The total number of protons and neutrons
   • The number of neutrons only
   • The number of protons only
   Show answer

   Answer: The total number of protons and neutrons

   Explanation: The mass number counts the particles in the nucleus: protons plus neutrons. Electrons are left out because their mass is so small.

9. 9.Magnesium has atomic number 12. How many electrons does a magnesium ion, Mg2+, have?

   • 12
   • 14
   • 2
   • 10
   Show answer

   Answer: 10

   Explanation: A neutral magnesium atom has 12 electrons. The 2+ charge means it has lost two of them, leaving 10.

10. 10.In every neutral atom, the number of electrons equals the number of neutrons.

    • True
    • False
    Show answer

    Answer: False

    Explanation: In a neutral atom the number of electrons equals the number of protons, so the charges cancel. The number of neutrons can be different, as in sodium-23 with 11 electrons and 12 neutrons.

11. 11.What is the maximum number of electrons the first electron shell can hold?

    • 1
    • 8
    • 2
    • 18
    Show answer

    Answer: 2

    Explanation: The first shell, closest to the nucleus, holds at most 2 electrons. In the simple shell model used at this level, the next two shells hold up to 8 each.

12. 12.Calcium has atomic number 20. What is its electron arrangement?

    • 2,18
    • 2,8,10
    • 2,8,9,1
    • 2,8,8,2
    Show answer

    Answer: 2,8,8,2

    Explanation: The 20 electrons fill the shells in order: 2 in the first, 8 in the second, 8 in the third, and the last 2 go into the fourth shell.

13. 13.Which element has atoms with the electron arrangement 2,8,7?

    • Sulfur
    • Chlorine
    • Fluorine
    • Argon
    Show answer

    Answer: Chlorine

    Explanation: 2 + 8 + 7 = 17 electrons, so the atomic number is 17: chlorine. Fluorine is 2,7, sulfur is 2,8,6 and argon is 2,8,8.

14. 14.In the gold foil experiment, most alpha particles went straight through the foil. What did this show?

    • An atom is mostly empty space
    • The nucleus contains neutrons
    • Atoms are solid spheres that cannot be divided
    • Electrons are arranged in shells
    Show answer

    Answer: An atom is mostly empty space

    Explanation: If most alpha particles pass through without being deflected, most of the atom must be empty. The few that bounced back showed a small, dense, positive nucleus.

15. 15.Isotopes of the same element have the same chemical properties because they have the same electron arrangement.

    • True
    • False
    Show answer

    Answer: True

    Explanation: Chemical reactions depend on electrons, mainly those in the outer shell. Isotopes have the same number of electrons arranged the same way, so they react in the same way, even though their masses differ.

16. 16.Which scientist showed in 1932 that the nucleus contains neutrons?

    • Ernest Rutherford
    • James Chadwick
    • Niels Bohr
    • J. J. Thomson
    Show answer

    Answer: James Chadwick

    Explanation: Chadwick identified the neutron in 1932, about twenty years after the nucleus itself was discovered. Thomson discovered the electron, Rutherford the nucleus, and Bohr proposed fixed energy levels.

17. 17.How did the plum pudding model describe the atom?

    • Electrons in fixed energy levels around a nucleus
    • A small, dense positive nucleus with electrons orbiting it
    • A tiny solid particle with no internal parts
    • A ball of positive charge with electrons embedded in it
    Show answer

    Answer: A ball of positive charge with electrons embedded in it

    Explanation: In the plum pudding model, negative electrons were scattered through a sphere of spread-out positive charge. The gold foil experiment later replaced it with the nuclear model.

18. 18.What was the key new idea in Bohr's model of the atom?

    • Electrons orbit the nucleus in fixed energy levels at set distances
    • Electrons sit inside a sphere of spread-out positive charge
    • The nucleus holds most of the atom's negative charge
    • Electrons can have any energy as they move around the nucleus
    Show answer

    Answer: Electrons orbit the nucleus in fixed energy levels at set distances

    Explanation: Bohr proposed that electrons can only occupy certain energy levels, or shells, at fixed distances from the nucleus. This explained why atoms give out light only at particular wavelengths.

19. 19.The radius of an atom's nucleus is roughly what fraction of the radius of the whole atom?

    • About 1/100
    • About 1/10
    • Less than 1/10,000
    • About 1/2
    Show answer

    Answer: Less than 1/10,000

    Explanation: A typical atom is about 0.1 nanometres across, while its nucleus is tens of thousands of times smaller. The nucleus takes up a tiny fraction of the atom's volume.

20. 20.Hydrogen-1, the most common isotope of hydrogen, has no neutrons.

    • True
    • False
    Show answer

    Answer: True

    Explanation: Hydrogen-1 has a mass number of 1 and an atomic number of 1, so its nucleus is a single proton with no neutrons. Deuterium (hydrogen-2) has one neutron.

21. 21.Why is the relative atomic mass of chlorine about 35.5 rather than a whole number?

    • Chlorine is a mixture of chlorine-35 and chlorine-37, with more chlorine-35
    • The electrons add about 0.5 to the mass
    • Each chlorine atom contains half a neutron
    • Chlorine-35 and chlorine-37 are present in equal amounts
    Show answer

    Answer: Chlorine is a mixture of chlorine-35 and chlorine-37, with more chlorine-35

    Explanation: Relative atomic mass is a weighted average of the isotopes' masses. About three quarters of chlorine atoms are chlorine-35 and one quarter chlorine-37, giving about 35.5; equal amounts would give 36.

22. 22.An element is 69% of an isotope with mass number 63 and 31% of an isotope with mass number 65. What is its relative atomic mass, to one decimal place?

    • 64.0
    • 63.6
    • 63.0
    • 64.4
    Show answer

    Answer: 63.6

    Explanation: Weighted average: (69 x 63 + 31 x 65) / 100 = (4347 + 2015) / 100 = 63.62, which rounds to 63.6. This is copper.

23. 23.In which period of the periodic table is an element with the electron arrangement 2,8,3?

    • Period 1
    • Period 2
    • Period 3
    • Period 4
    Show answer

    Answer: Period 3

    Explanation: The period number equals the number of occupied electron shells. 2,8,3 uses three shells, so the element (aluminium) is in period 3.

24. 24.Which pair of atoms are isotopes of each other?

    • Argon-40 and calcium-40
    • Carbon-14 and nitrogen-14
    • Sodium-23 and magnesium-24
    • Carbon-12 and carbon-14
    Show answer

    Answer: Carbon-12 and carbon-14

    Explanation: Isotopes are atoms of the same element. Carbon-12 and carbon-14 both have 6 protons but 6 and 8 neutrons; the other pairs are different elements.

25. 25.The mass number of an atom can be smaller than its atomic number.

    • True
    • False
    Show answer

    Answer: False

    Explanation: The mass number is protons plus neutrons, and the atomic number is protons alone. Since the number of neutrons cannot be negative, the mass number is never smaller than the atomic number.