Year 10 Science | Victorian Curriculum 2.0
Periodic table & atomic properties
Topic 03 | Chemical sciences | Answer key

Year 10 answers

Fluency

Table literacy

    1. A group is a vertical column; a period is a horizontal row. Group members share valence-electron count; period members share their outermost shell number.
    2. Hydrogen, lithium, sodium, potassium, rubidium. (H is sometimes placed separately.)
    3. Helium, neon, argon, krypton.
    4. Metals: left and centre. Non-metals: upper right.
    5. Elements on the diagonal “staircase” with some metallic and some non-metallic properties. Examples: silicon, germanium, boron.
    6. Their outer electron shells are full, so they have no tendency to gain, lose or share electrons.
Fluency

Electron configuration

    1. (a) C: 2,42, 4. (b) O: 2,62, 6. (c) Ne: 2,82, 8. (d) Na: 2,8,12, 8, 1.
    2. Group 16. Sulfur.
    3. Group 1. Potassium.
    4. 55 valence electrons.
    5. Mg (2,8,22, 8, 2): two electrons in inner shell, eight in second, two in outer.
Fluency

Ions and bonding

    1. Group 1: +1+1. Group 2: +2+2.
    2. Group 17: −1-1. Group 16: −2-2.
    3. Ionic — a metal (Na) bonded with a non-metal (Cl); electrons transfer.
    4. Covalent — both elements are non-metals (C and H); electrons are shared.
    5. MgO.
Reasoning

Trends and explain

    1. Down Group 1, outer electrons are further from the nucleus and more easily lost, so metals become more reactive. Down Group 17, atoms are larger and less able to attract an extra electron, so non-metal reactivity falls.
    2. Sodium is more reactive. Na loses 11 electron to form Na+^+; Mg must lose 22 electrons to form Mg2+^{2+}, which requires more energy.
    3. They have the same number of valence electrons; chemistry is determined by the outer shell.
    4. Atoms form ions to reach a full outer shell (the noble-gas configuration), which is energetically stable.
    5. Helium has only 22 electrons, but its outer shell (11s) is full at 22. It is chemically inert like the other noble gases, so it belongs in Group 18 by behaviour.
Problem solving

Applications

    1. Lithium is the lightest metal and has the highest energy-to-mass ratio; it is also less violently reactive than sodium or potassium when managed in non-aqueous electrolytes, and its ion is small enough to move quickly between electrodes.
    2. Argon is inert — it will not react with the hot filament. Oxygen would oxidise (burn) the filament; nitrogen is less reactive but still less safe than argon.
    3. HF is most vigorous; going down Group 17 reactivity decreases, so F >> Cl >> Br.
    4. (a) KCl, ionic. (b) CaO, ionic. (c) CO2_2, covalent. (d) NH3_3, covalent.
Reasoning

Challenge

    1. The table’s pattern meant each gap had predictable properties from its neighbours (mass, melting point, reactivity). The switch to atomic number resolved anomalies (e.g. tellurium and iodine appear out of order by mass but in the right order by proton count), and atomic number reflects the true physical basis of chemistry.
    2. Group 1 and 17 elements are typically one electron away from a noble-gas configuration, giving one clearly preferred ion. Transition metals have inner-shell (d-orbital) electrons of similar energy that can also be removed, giving multiple stable ions.
    3. Na loses its one outer-shell electron, collapsing to the inner 2,82, 8 shell — much smaller. Cl gains an electron into its outer shell; electron-electron repulsion and a weaker effective nuclear pull per electron expand the radius.
    4. Water is polar: the O end is slightly negative, the H end slightly positive. Polar water molecules surround the Na+^+ and Cl−^- ions, pulling them out of the crystal lattice — dissolution.
Year 10 Science study companion | Answer key