Atomic Structure

Sample questions

Showing 10 of 70 questions from this chapter. The full bank is in the chapter test below.

1. 1

   Who concluded from the X-rays emitted by elements bombarded with cathode rays that atomic number is a fundamental property of an element?

   • A.✓ Moseley (correct answer)
   • B.Bohr
   • C.Schrodinger
   • D.Rutherford

   Why: In 1913 Moseley showed that the square root of the X-ray frequency is directly proportional to the atomic number Z of an element. Bohr and Schrodinger contributed models of the atom, but not this relationship.
2. 2

   Which property of an atom does its proton number represent?

   • A.The total number of electrons it contains
   • B.The sum of its protons and neutrons
   • C.The number of neutrons in its nucleus
   • D.✓ The number of protons in its nucleus (correct answer)

   Why: Atomic number and proton number mean the same thing, namely the number of protons in the nucleus. The sum of protons and neutrons is the nucleon (mass) number, and the electron count of an ion differs from the proton count.
3. 3

   Which pair of terms is used for the very same quantity?

   • A.Atomic number and nucleon number
   • B.Mass number and proton number
   • C.✓ Mass number and nucleon number (correct answer)
   • D.Proton number and neutron number

   Why: Mass number and nucleon number both stand for the total number of protons and neutrons in the nucleus. Atomic number is the proton number, which is a different quantity.
4. 4

   Which relation correctly gives the number of neutrons N in an atom?

   • A.N = A + Z
   • B.N = A x Z
   • C.N = Z - A
   • D.✓ N = A - Z (correct answer)

   Why: Nucleon number is the sum of protons and neutrons, A = Z + N, so N = A - Z. The reversed form N = Z - A would give a negative number for every element.
5. 5

   An atom is represented by the symbol 27-Al-13 (A = 27, Z = 13). What is the number of neutrons in it?

   • A.✓ 14 (correct answer)
   • B.13
   • C.27
   • D.40

   Why: N = A - Z = 27 - 13 = 14. Choosing 13 is the mistake of quoting the proton number, and 27 is the total number of nucleons, not the neutrons alone.
6. 6

   How many electrons are present in the $\ce{Al3+}$ ion formed when an aluminium atom (Z = 13, A = 27) loses three electrons?

   • A.13
   • B.✓ 10 (correct answer)
   • C.16
   • D.14

   Why: A neutral aluminium atom has 13 electrons and a 3+ ion has lost three of them, leaving 13 - 3 = 10. The number of protons (13) and neutrons (14) is unchanged by ion formation.
7. 7

   The chloride ion $\ce{Cl-}$ is formed from 35-Cl-17. What is the number of electrons in this ion?

   • A.16
   • B.35
   • C.✓ 18 (correct answer)
   • D.17

   Why: A chlorine atom has 17 electrons and gains one to give 18. Quoting 17 ignores the added electron, and 35 is the nucleon number.
8. 8

   For the oxide ion $\ce{O2-}$ formed from the atom 16-O-8, which set of numbers is correct?

   • A.8 protons, 8 neutrons, 8 electrons
   • B.8 protons, 16 neutrons, 10 electrons
   • C.10 protons, 8 neutrons, 8 electrons
   • D.✓ 8 protons, 8 neutrons, 10 electrons (correct answer)

   Why: The atom has 8 protons and 16 - 8 = 8 neutrons, and the 2- charge means two extra electrons, giving 10. Gaining electrons never changes the proton or neutron count.
9. 9

   Which one of the following is a fundamental particle with no charge and a mass slightly greater than that of a proton?

   • A.✓ Neutron (correct answer)
   • B.Electron
   • C.Proton
   • D.Positron

   Why: The neutron carries zero charge and its mass is 1.0087 amu, slightly larger than the proton's 1.0073 amu. The electron is far lighter than both.
10. 10

    What is the relative charge and approximate mass of an electron in atomic mass units?

    • A.Relative charge -1, mass 1.0073 amu
    • B.Relative charge +1, mass 0.00055 amu
    • C.Relative charge 0, mass 1.0087 amu
    • D.✓ Relative charge -1, mass 0.00055 amu (correct answer)

    Why: The electron has relative charge -1 and a mass of $5.4858 \times 10^{-4}$ amu, which is about 0.00055 amu. The other values belong to the proton and the neutron.