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

  2. 2.Nitrogen's electronic configuration is 2, 5. What is its valency? Answer with a number.

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

    Groups: Positive charge · Negative charge · No charge

    • Proton
    • Electron
    • Neutron

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

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

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

  6. 6.Why do the isotopes of an element behave the same way chemically?

    • a) They have the same melting and boiling points
    • b) They have the same number of electrons, arranged the same way
    • c) They have the same mass number
    • d) They have the same number of neutrons

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

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

  8. 8.Two atoms have the same atomic number but different mass numbers. What are they called?

    • a) Two molecules of one compound
    • b) Ions of the same element
    • c) Isotopes of the same element
    • d) Two different elements

Answer key — Year 9 Science — Inside the atom

  1. 1. 2
  2. 2. 3
  3. 3. Proton → Positive charge; Electron → Negative charge; Neutron → No charge
  4. 4. 30
  5. 5. c) Tritium
  6. 6. b) They have the same number of electrons, arranged the same way
  7. 7. c) It is largely unreactive, its octet being complete
  8. 8. c) Isotopes of the same element