The Periodic Table: Groups, Periods, Metals and Non-Metals — Answers
Answer sheet with model answers and success criteria for the 9th Grade chemical sciences worksheet.
Success TutoringWorksheetsAnswer sheet9th Grade · Science · Chemical SciencesThe Periodic Table: Groups, Periods, Metals and Non-Metals — Answers
Part A: How the table is arranged
The periodic table lists the elements in order of atomic number. The vertical columns are groups and the horizontal rows are periods.
For the main groups, elements in the same group have the same number of outer-shell electrons (group 1 has 1, group 2 has 2, group 17 has 7, group 18 has a full outer shell). The period number equals the number of electron shells.
- Amass number
- Batomic number
- Cdensity
- Dmelting point
Answer: atomic number
The modern periodic table is arranged by atomic number (the number of protons).
Answer: Period 3, because its electrons fill 3 shells. Group 2, because it has 2 electrons in its outer shell.
Answer: 2, 5 — nitrogen (atomic number 7).
Answer: True
They have the same number of outer-shell electrons, and the outer electrons decide how an element reacts.
Part B: Metals and non-metals
- Shiny when freshly cut
- Good conductors of electricity
- Malleable and ductile
- Brittle when solid
- Mostly poor conductors of heat
- Non-metals
- Non-metals
- Metals
- Metals
- Metals
Answer: Shiny when freshly cut → Metals; Good conductors of electricity → Metals; Malleable and ductile → Metals; Brittle when solid → Non-metals; Mostly poor conductors of heat → Non-metals
- Ametal
- Bnon-metal
- Cnoble gas
- Dalloy
Answer: non-metal
Dull, brittle and non-conducting are typical non-metal properties (for example sulfur).
Answer: A metalloid (semi-metal).
Answer: Metals are on the left and in the center (most elements are metals). Non-metals are on the right, with metalloids along the staircase line between them. Hydrogen is a non-metal placed at the top left.
Part C: Trends in groups
Group 1, the alkali metals, are soft metals that react quickly with water to produce a metal hydroxide and hydrogen gas. Reactivity increases down the group. Melting points (°C): lithium 181, sodium 98, potassium 63, rubidium 39.
Group 17, the halogens, are reactive non-metals made of two-atom molecules (F₂, Cl₂, Br₂, I₂). Reactivity decreases down the group. Boiling points (°C): fluorine −188, chlorine −34, bromine 59, iodine 184.
Group 18, the noble gases, such as helium, neon and argon, are colorless gases that hardly react at all.
Alkali metals and halogens are handled only by a teacher, in small amounts and with safety equipment.
Answer: Melting point decreases down the group; caesium about 28 °C (accept 20–35 °C)
- 181 → 98 → 63 → 39: each value is lower
- The drops are getting smaller (83, 35, 24), so the next drop is probably about 10–20 °C
- Prediction: about 28 °C (actual value 28 °C)
Answer: 2Na + 2H₂O → 2NaOH + H₂
- Left: Na 2, H 4, O 2
- Right: Na 2, O 2, H 2 + 2 = 4 (balanced)
Answer: Further down the group, atoms have more electron shells, so the single outer electron is further from the nucleus and more shielded. It is held less strongly and lost more easily, so the metal reacts more readily.
Answer: Fluorine: gas. Chlorine: gas. Bromine: liquid (melting point −7 °C, boiling point 59 °C). Iodine: solid.
- AFluorine
- BChlorine
- CBromine
- DIodine
Answer: Fluorine
Halogens react by gaining one electron. Fluorine's atoms are smallest, so the nucleus attracts an extra electron most strongly. Reactivity decreases down group 17.
Answer: Their atoms already have a full outer shell of electrons, so they do not need to gain, lose or share electrons.
Part D: Predict and explain
Model answer: Potassium would react more vigorously than sodium: it would fizz faster, move around quickly on the surface, melt into a ball and the hydrogen produced would catch fire with a lilac flame. Word equation: potassium + water → potassium hydroxide + hydrogen. Both atoms have one outer electron, which they lose when they react. Potassium has four shells while sodium has three, so potassium's outer electron is further from the nucleus and more shielded by inner electrons. It is attracted less strongly and lost more easily, so potassium is more reactive.
Success criteria:
- Predicts a more vigorous reaction with a relevant observation
- Correct word equation
- Both have one outer electron that is lost in reactions
- Potassium's outer electron is further from the nucleus, so it is lost more easily
Marking tips
- Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
- For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
- Celebrate what went well first, then pick one thing to work on next.