CIE iGCSE Co-Ordinated Science C2.2 Atomic structure and the Periodic Table Exam Style Questions Paper 3
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C2.2 — Atomic structure and the Periodic Table (Part (a)(i) & (a)(ii))
• Topic C7.1 — Characteristic properties of acids and bases (Part (b)(i) & (b)(ii))
• Topic C6.2 — Rate of reaction (Part (c))
• Topic C1.1 — Solids, liquids and gases (Part (d))
▶️ Answer/Explanation
(a)(i)
20
The number of protons is equal to the atomic number of the element, which is 20 for calcium. Ion formation involves gaining or losing electrons only — the proton number never changes and always identifies the element.
(a)(ii)
2
Calcium is in Group II and has 2 electrons in its outer shell. It loses these 2 outer-shell electrons to achieve the stable electron configuration of argon, forming the $\text{Ca}^{2+}$ ion with 18 electrons remaining.
(b)(i)
1. calcium sulfate ($\text{CaSO}_4$)
2. water ($\text{H}_2\text{O}$)
The reaction between a carbonate and an acid is a neutralisation reaction that always produces a salt, water, and carbon dioxide. Here the salt formed is calcium sulfate, since sulfuric acid provides the sulfate ion that replaces the carbonate in the product.
(b)(ii)
• $1.00\,\text{g}$ of $\text{CaCO}_3$ produces $240\,\text{cm}^3$ of $\text{CO}_2$
• Mass of $\text{CaCO}_3 = 1.00 \times \dfrac{360}{240}$
• $\boxed{\text{Mass of CaCO}_3 = 1.50\,\text{g}}$
The volume of gas produced is directly proportional to the mass of calcium carbonate used under constant conditions. Since $360\,\text{cm}^3$ is 1.5 times $240\,\text{cm}^3$, the mass required is simply $1.00 \times 1.5 = 1.50\,\text{g}$.
(c)
The two changes that decrease the rate are: decreasing the concentration of acid (fewer acid particles per unit volume reduces collision frequency) and using larger pieces of calcium carbonate (smaller surface area means fewer collisions per second between acid particles and the solid). Increasing temperature and adding a catalyst would both increase the rate instead.
(d)
• able to be compressed → G
• able to diffuse → G
• able to flow → G
• has a fixed shape → S
• has a fixed volume → S
Gas particles are widely spaced and move rapidly and randomly, allowing compression, diffusion, and flow. Solid particles are held in fixed positions in a closely packed lattice, giving them both a definite shape and a definite volume that cannot easily be changed.
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic C2.2 — Atomic structure and the Periodic Table (Part (a))
• Topic C8.1 — Arrangement of elements (Part (b)(i) & (b)(ii))
• Topic C8.2 — Group I properties (Part (b)(iii) & (b)(v))
• Topic C8.3 — Group VII properties (Part (b)(vi))
• Topic C8.5 — Noble gases (Part (b)(iv))
▶️ Answer/Explanation
(a)
The elements are listed in order of their proton / atomic number.
Moving from left to right across the Periodic Table, the elements become less metallic.
These metals form coloured compounds and are known as the transition elements.
As you move across a period, the increasing number of outer-shell electrons makes it progressively harder for atoms to lose electrons and behave as metals. Transition elements sit in the central block of the Periodic Table and are characterised by variable oxidation states, catalytic behaviour, and the formation of coloured ions and compounds.
(b)(i)
S, T, or V
S represents hydrogen (Group I, Period 1), which exists as the diatomic molecule $\text{H}_2$ at room temperature. T and V are halogens (Group VII) which also exist as diatomic molecules — fluorine ($\text{F}_2$) and chlorine ($\text{Cl}_2$) respectively — and are gases at room temperature. Any one of these three letters is a correct answer.
(b)(ii)
P, Q, or R
P, Q, and R are all metals located in Group I (alkali metals), and metals are solids at room temperature. They represent lithium, sodium, and potassium respectively, all of which have melting points well above room temperature. Any one of these three letters is a correct answer.
(b)(iii)
P, Q, or R
Alkali metals occupy Group I of the Periodic Table, excluding hydrogen (S, Period 1) which is a non-metal. P (lithium, Period 2), Q (sodium, Period 3), and R (potassium, Period 4) are all alkali metals with one outer-shell electron, making them highly reactive. Any one of these three letters is a correct answer.
(b)(iv)
X, Y, or Z
Noble gases are found in Group VIII (Group 0) of the Periodic Table and have a completely full outer electron shell. X represents helium (Period 1), Y represents neon (Period 2), and Z represents argon (Period 3) — all of which are monatomic, colourless, and extremely unreactive gases at room temperature. Any one of these three letters is a correct answer.
(b)(v)
R
Reactivity of alkali metals increases down Group I as the outer electron is further from the nucleus and more easily lost. Among the Group I metals shown, R sits lowest in the group (Period 4 — potassium) and is therefore the most reactive metal in Fig. 5.1.
(b)(vi)
T
Reactivity of halogens decreases down Group VII as each successive element has a greater atomic radius, making it harder to attract an additional electron. T sits higher in the group (Period 2 — fluorine) than V (Period 3 — chlorine), making T the most reactive halogen shown in Fig. 5.1.