← Back to the activity

Class 9 Science — Inside the atom

Count protons, neutrons and electrons from an atomic number and a mass number, fill the shells and read off a valency, and say what makes two atoms isotopes.

Name: ________________________

Before you start

The parts of an atom, each one named.

1234
  1. 1. The centre
  2. 2. The nearest ring
  3. 3. The middle ring
  4. 4. The furthest ring

The centre is the nucleus, holding the protons and neutrons. The rings are the shells, filled from the inside out: K first, then L, then M.

  1. 1.An atom of atomic number 26 has 56 nucleons. How many neutrons has it? Answer with a number.

  2. 2.Put the shells in the order electrons fill them, starting from The K shell, nearest the nucleus.

    • The M shell
    • The K shell, nearest the nucleus
    • The N shell
    • The L shell

  3. 3.Oxygen's electronic configuration is 2, 6. What is its valency? Answer with a number.

  4. 4.An atom's outermost shell holds 8 electrons. What does the chapter say to expect of it?

    • a) It reacts readily, needing to gain eight more
    • b) It has a valency of eight
    • c) It is largely unreactive, its octet being complete
    • d) It reacts readily, needing to shed its eight

  5. 5.Match each element to its symbol.

    • Iron
    • Sodium
    • Potassium
    • Silver
    • Gold
    • K
    • Ag
    • Na
    • Au
    • Fe

  6. 6.Sort each subatomic particle by the charge it carries.

    Groups: Positive charge · Negative charge · No charge

    • Proton
    • Electron
    • Neutron

  7. 7.Using the rule that a shell numbered n holds at most 2n² electrons, what is the greatest number the M shell, where n is 3, can hold? Answer with a number.

  8. 8.Hydrogen occurs as three isotopes. Which one has two neutrons?

    • a) Each of the three has two
    • b) Protium
    • c) Tritium
    • d) Deuterium

Answer key — Class 9 Science — Inside the atom

  1. 1. 30
  2. 2. 1. The K shell, nearest the nucleus 2. The L shell 3. The M shell 4. The N shell
  3. 3. 2
  4. 4. c) It is largely unreactive, its octet being complete
  5. 5. Iron → Fe; Sodium → Na; Potassium → K; Silver → Ag; Gold → Au
  6. 6. Proton → Positive charge; Electron → Negative charge; Neutron → No charge
  7. 7. 18
  8. 8. c) Tritium