Science 9 · Unit 2: Properties of materials · Cambridge Lower Secondary Science Stage 9

Questions

1. 1. Which ion is the same as the atom except that it has one fewer electron?

   • a negative ion with a charge of 1−
   • an atom of the next element
   • a positive ion with a charge of 2+
   • a positive ion with a charge of 1+
   Check

2. 2. Match each atom with the ion it forms.

   • sodium (2,8,1)
   • magnesium (2,8,2)
   • oxygen (2,6)
   • chlorine (2,8,7)

   • O²⁻
   • Na⁺
   • Cl⁻
   • Mg²⁺
   Check

3. 3. What is an ionic bond?

   • a pair of electrons shared between two atoms
   • the attraction between two positive ions
   • the force holding protons and neutrons together
   • the electrostatic attraction between a positive ion and a negative ion
   Check

4. 4. Which of these compounds is held together by ionic bonds?

   • magnesium oxide, MgO
   • methane, CH₄
   • carbon dioxide, CO₂
   • water, H₂O
   Check

5. 5. What is a covalent bond?

   • an electron passed from a metal to a non-metal
   • two nuclei joined together
   • the attraction between a positive and a negative ion
   • a pair of electrons shared between two atoms
   Check

6. 6. How does a hydrogen molecule, H₂, form?

   • The two nuclei join to make one atom.
   • Each atom loses its electron.
   • One hydrogen atom gives its electron to the other.
   • The two hydrogen atoms share their electrons, so each has two in its shell.
   Check

7. 7. In a dot and cross diagram of sodium chloride, why are the electrons drawn as dots and crosses?

   • to show positive and negative electrons
   • because dots are protons and crosses are electrons
   • to show which electrons are in the nucleus
   • to show which atom each electron came from
   Check

8. 8. A lithium atom has the electronic structure 2,1. Which shell has the highest energy level?

   • the nucleus
   • Both shells have the same energy.
   • the inner (first) shell, with two electrons
   • the outer (second) shell, with one electron
   Check

9. 9. A lithium atom (2,1) forms an ion. What is the electronic structure of the lithium ion?

   • 2
   • 1
   • 2,1
   • 2,2
   Check

10. 10. What is the symbol for a lithium ion?

    • Li²⁺
    • Li⁺
    • Li⁻
    • Li
    Check

11. 11. A fluorine atom is 2,7. What is the electronic structure of a fluorine ion?

    • 2,7
    • 2
    • 2,6
    • 2,8
    Check

12. 12. What is the symbol for a fluorine ion?

    • F
    • F²⁻
    • F⁻
    • F⁺
    Check

13. 13. Sodium has atomic number 11. What happens when a sodium atom becomes an ion?

    • It loses 1 electron and becomes Na⁺ (2,8).
    • It loses 1 proton and becomes Na⁺ (2,8,1).
    • It gains 1 electron and becomes Na⁻ (2,8,2).
    • It gains 7 electrons and becomes Na⁷⁻ (2,8,8).
    Check

14. 14. Chlorine has atomic number 17. What is the electronic structure of a chloride ion, Cl⁻?

    • 2,8,8
    • 2,8,6
    • 2,8
    • 2,8,7
    Check

15. 15. A chlorine atom has 17 protons and mass number 35. How many neutrons does it have?

    • 52
    • 35
    • 17
    • 18
    Check

16. 16. What holds the electrons in place around the nucleus of an atom?

    • the electrons sticking to each other
    • magnetic forces from the neutrons
    • gravity from the nucleus
    • electrostatic forces between the positive protons and the negative electrons
    Check

17. 17. Why do atoms form ions?

    • Losing or gaining electrons gives them a full outer shell, which is more stable.
    • To change into a different element.
    • To make their nucleus bigger.
    • Ions are lighter than atoms.
    Check

18. 18. A calcium atom (2,8,8,2) forms an ion. What is the electronic structure of the calcium ion?

    • 2,8,8
    • 2,8,8,4
    • 2,8,10
    • 2,8,8,2
    Check

19. 19. Calcium chloride is CaCl₂. Why are there two chloride ions for each calcium ion?

    • Chlorine atoms are smaller than calcium atoms.
    • Ca²⁺ has a charge of 2+ and each Cl⁻ has 1−, so two are needed to balance it.
    • Chlorine is a gas, so it comes in pairs.
    • Calcium has two shells of electrons.
    Check