Home / iGCSE Chemistry (0620) Theory (Core):2.2 Atomic structure and the Periodic Table: Exam Style Questions Paper 3

iGCSE Chemistry (0620) Theory (Core):2.2 Atomic structure and the Periodic Table: Exam Style Questions Paper 3- New Syllabus

iGCSE Chemistry Theory (Core) Paper 3 - All Chapters

Question

The symbol for an atom of xenon is shown:
\( \frac{131}{54}\mathrm{Xe} \)
(a) Complete Table 2.1 to show the number of neutrons and nucleons in one atom of \( \frac{131}{54}\mathrm{Xe} \).
(b) Xenon is a gas at room temperature and pressure.
A sample of xenon is placed in a sealed syringe with a freely moving plunger.
Complete Table 2.2 to show the effect, if any, on the volume of xenon when:
  • the temperature of the xenon is decreased
  • the pressure of the xenon is decreased.
Use the words increases, decreases or no change in your answer.
(c) When xenon is cooled, it becomes a solid.
Describe the arrangement and motion of the particles in solid xenon.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• Topic 2.2 — Atomic structure and the Periodic Table (Part (a))
• Topic 1.1 — Solids, liquids and gases (Parts (b), (c))

▶️ Answer/Explanation

(a)
Number of neutrons: 77
Number of nucleons: 131

The mass number (nucleon number) is given as 131, which represents the total number of protons and neutrons (nucleons). The atomic (proton) number is 54. Therefore, the number of neutrons is calculated as \( 131 – 54 = 77 \).

(b)
Temperature is decreased: decreases
Pressure is decreased: increases

According to the kinetic particle theory, decreasing the temperature reduces the average kinetic energy of the gas particles, causing them to move slower and occupy less volume. Conversely, decreasing the pressure allows the gas to expand, increasing the volume. (Note: The mark scheme specifies this follows Charles’s and Boyle’s laws for a flexible container.)

(c)
Particle arrangement: regular / in rows
Particle motion: vibrate

In a solid state, atoms have low energy. They are held in fixed positions by strong forces and are arranged in a regular, repeating lattice. The particles cannot move freely; they can only vibrate about their fixed points.

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