The method and the results are on the periodicity lab. Do the analysis yourself first, then check the answers below.
Quick answer: Periodicity means that properties repeat across the periodic table. These answers go with the Chemistry 11-12 lab on periodicity: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
These model answers use the sample readings in the results table. Compare your own calculations and explanations with them, paying attention to the way structure and bonding explain each observation and to the uncertainty analysis.
Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: A Level 3.2.1
It limits the current so the cells are not short-circuited when a low-resistance metal is connected, keeps the current within the ammeter range and prevents the sample heating, which would change its resistance. It protects the equipment and keeps the test fair.
Question 3 Ranking by conductivity
Mg ≈ Al > Si > S. Magnesium and aluminium have giant metallic lattices with delocalised electrons that carry charge. Silicon has a giant covalent lattice in which almost all electrons are held in bonds. Sulfur consists of S₈ molecules with no mobile charge carriers.
Question 4 Why silicon is in the middle
A few electrons in silicon have enough energy to escape from bonds and move, so it is a semiconductor. Sulfur’s electrons are firmly localised. Warming silicon frees more electrons, so the current increases, the opposite of a metal, whose resistance rises with temperature.
Question 5 Malleable or brittle
In a metal the layers of cations can slide past each other while the delocalised electrons keep the lattice bonded, so the metal bends. In silicon the directional covalent bonds are fixed and break along a plane when the lattice is deformed, so it shatters.
Question 6 Uncertainty
ΔR = 3.0 × 0.001 / (0.297)² = 0.034 Ω, so Mg = 0.10 ± 0.03 Ω and Al (same method, 0.034 Ω) = 0.14 ± 0.03 Ω. The ranges overlap, so this experiment cannot separate magnesium from aluminium.
Question 7 Improving the method
Oxide layers on Mg and Al add resistance: sand the surface just before the test. Poor clip contact adds resistance: use the same clamps at the same distance and add a voltmeter across the sample to measure its resistance directly.
Question 8 Prediction
Sodium conducts because it has a giant metallic lattice with one delocalised electron per atom. Liquid chlorine does not because it contains neutral Cl₂ molecules and no mobile charges.
