Atomic Models, Subatomic Particles and Isotopes

Attempt the quiz above first, then review every question with its correct answer and a short explanation below.

1. Q1.The nucleus of the atom was discovered by:

   • A.Ernest Rutherford✓ Correct Answer
   • B.J. J. Thomson
   • C.James Chadwick
   • D.Niels Bohr

   Explanation: Rutherford's gold foil experiment revealed a small dense nucleus.

2. Q2.The neutron was discovered by:

   • A.Ernest Rutherford
   • B.Robert Millikan
   • C.James Chadwick✓ Correct Answer
   • D.Henry Moseley

   Explanation: Chadwick found it in 1932.

3. Q3.The charge on a neutron is:

   • A.positive
   • B.negative
   • C.variable
   • D.zero✓ Correct Answer

   Explanation: Neutrons are electrically neutral.

4. Q4.The atomic number of an element is equal to the number of:

   • A.neutrons
   • B.nucleons
   • C.protons✓ Correct Answer
   • D.molecules

   Explanation: It defines the identity of an element.

5. Q5.The mass number of an atom is the sum of its:

   • A.protons and neutrons✓ Correct Answer
   • B.protons and electrons
   • C.electrons and neutrons
   • D.electrons only

   Explanation: Protons and neutrons are together called nucleons.

6. Q6.The plum pudding model of the atom was proposed by:

   • A.Rutherford
   • B.Bohr
   • C.J. J. Thomson✓ Correct Answer
   • D.Dalton

   Explanation: Electrons were pictured embedded in a positive sphere.

7. Q7.Isotopes are atoms of the same element with the same:

   • A.mass number but different atomic numbers
   • B.neutrons only
   • C.atomic number but different mass numbers✓ Correct Answer
   • D.electrons but different protons

   Explanation: They differ in the number of neutrons.

8. Q8.Isobars are atoms with the same:

   • A.atomic number but different mass numbers
   • B.mass number but different atomic numbers✓ Correct Answer
   • C.number of neutrons
   • D.chemical properties

   Explanation: Argon-40 and calcium-40 are examples.

9. Q9.Isotones are atoms with the same number of:

   • A.protons
   • B.electrons
   • C.neutrons✓ Correct Answer
   • D.nucleons

   Explanation: They have different atomic numbers.

10. Q10.Bohr's model of the atom states that electrons revolve in:

    • A.random paths
    • B.the nucleus
    • C.straight lines
    • D.fixed circular orbits with definite energies✓ Correct Answer

    Explanation: Energy is emitted or absorbed only when electrons jump between orbits.

11. Q11.The maximum number of electrons in the K shell is:

    • A.2✓ Correct Answer
    • B.8
    • C.18
    • D.32

    Explanation: The maximum in a shell is 2n², and n = 1 here.

12. Q12.The maximum number of electrons in the L shell is:

    • A.2
    • B.8✓ Correct Answer
    • C.18
    • D.32

    Explanation: 2n² with n = 2 gives 8.

13. Q13.Which isotope of hydrogen has no neutron?

    • A.deuterium
    • B.protium✓ Correct Answer
    • C.tritium
    • D.none of them

    Explanation: Protium is the only common hydrogen isotope with just one proton and no neutron.

14. Q14.Which isotope is used for radiocarbon dating?

    • A.carbon-12
    • B.uranium-235
    • C.iodine-131
    • D.carbon-14✓ Correct Answer

    Explanation: Its radioactive decay gives the age of organic remains.

15. Q15.The number of valence electrons in a sodium atom is:

    • A.2
    • B.1✓ Correct Answer
    • C.8
    • D.11

    Explanation: Its configuration is 2, 8, 1.

16. Q16.The charge on a proton is:

    • A.negative
    • B.zero
    • C.double that of an electron
    • D.positive and equal in magnitude to that of an electron✓ Correct Answer

    Explanation: The two charges make a neutral atom.

17. Q17.Rutherford's alpha-particle scattering experiment used a thin foil of:

    • A.gold✓ Correct Answer
    • B.silver
    • C.copper
    • D.iron

    Explanation: Most particles passed straight through, a few were deflected sharply.

18. Q18.Heisenberg's uncertainty principle states that it is impossible to know simultaneously and exactly an electron's:

    • A.charge and mass
    • B.spin and colour
    • C.energy and shape
    • D.position and momentum✓ Correct Answer

    Explanation: It limits how precisely both can be defined.

19. Q19.Pauli's exclusion principle states that no two electrons in an atom can have:

    • A.the same charge
    • B.the same set of four quantum numbers✓ Correct Answer
    • C.the same mass
    • D.the same shell

    Explanation: So an orbital holds at most two electrons of opposite spin.

20. Q20.The fractional atomic mass of chlorine (35.5) arises because of its:

    • A.isotopes chlorine-35 and chlorine-37✓ Correct Answer
    • B.isobars
    • C.allotropes
    • D.impurities

    Explanation: It is the weighted average of the isotopes by natural abundance.