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IBDP Chemistry -Structure 1.2 The nuclear atom - IB Style Questions For SL Paper 2 -FA 2025

IB DP Chemistry SL Paper 2 - All Topics

Question

Iron has three main naturally occurring isotopes which can be investigated using a mass spectrometer.
A sample of iron has the following isotopic composition by mass.
Isotope\(^{54}\mathrm{Fe}\)\(^{56}\mathrm{Fe}\)\(^{57}\mathrm{Fe}\)
Relative abundance / %5.9591.882.17
a. Calculate the relative atomic mass of iron based on this data, giving your answer to two decimal places. [2]
b. Calculate the number of electrons in the ion \(^{56}\mathrm{Fe}^{2+}\). [1]
c. Describe the bonding in iron and explain the electrical conductivity and malleability of the metal. [4]

Most-appropriate topic codes (IB Chemistry 2025):

• Structure 1.1: Introduction to the particulate nature of matter — part a
• Structure 1.2: Atomic structure and electron configuration — part b
• Structure 2.1: Metallic bonding and properties — part c
▶️ Answer/Explanation
Detailed solution

a. [2]
\[ \text{Relative atomic mass} = \frac{(54 \times 5.95) + (56 \times 91.88) + (57 \times 2.17)}{100} \] \[ = 55.90 \]

b. [1]
Iron has atomic number \(26\).
The ion \(^{56}\mathrm{Fe}^{2+}\) has lost two electrons.
Number of electrons \(= 26 – 2 = \mathbf{24}\).

c. [4]
Iron exhibits metallic bonding, consisting of a lattice of positive metal ions surrounded by a sea of delocalized electrons.

Electrical conductivity: The delocalized electrons are free to move through the lattice and carry charge.

Malleability: Layers of metal ions can slide past each other without breaking the metallic bonds because the attraction between ions and electrons remains.

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