Home / AS & A Level Chemistry 9.1 Periodicity of physical properties of the elements in Period 3 Exam Style Practice Questions Paper 1
Which graph correctly shows the relative melting points and electronegativities of the Period 3 elements magnesium, aluminium, silicon and phosphorus?
Correct Answer: \( \boxed{\mathrm{B}} \)
Across Period 3:
Graph B correctly represents both the melting point trend and the increase in electronegativity across the period.
Therefore, the correct answer is (B).
X and Y are different elements in Period 3.
Atoms of X and Y each have only one completely filled orbital in their highest occupied energy sub-shell.
Y has a greater first ionisation energy than X.
Which row shows the structure and bonding in X and Y?
| X | Y | |
|---|---|---|
| A | giant metallic | giant metallic |
| B | giant metallic | simple molecular |
| C | giant covalent | simple molecular |
| D | simple molecular | simple molecular |
Correct Answer: \( \boxed{\mathrm{B}} \)
The Period 3 elements with only one completely filled orbital in their highest occupied sub-shell are magnesium (\(\mathrm{3s^2}\)) and sulfur (\(\mathrm{3p^4}\)).
Sulfur has a higher first ionisation energy than magnesium.
Magnesium has a giant metallic structure, while sulfur exists as simple molecular \(\mathrm{S_8}\) molecules.
Therefore, the correct answer is (B).
Sodium and sulfur react together to form sodium sulfide, \(\mathrm{Na_2S}\).
How do the atomic radius and ionic radius of sodium compare with those of sulfur?
| Atomic radius | Ionic radius | |
|---|---|---|
| A | sulfur is greater | sodium is greater |
| B | sulfur is greater | sulfur is greater |
| C | sodium is greater | sodium is greater |
| D | sodium is greater | sulfur is greater |
Correct Answer: \( \boxed{\mathrm{D}} \)
Across Period 3, atomic radius decreases from sodium to sulfur because nuclear charge increases while the number of occupied electron shells remains the same.
Therefore, sodium has the larger atomic radius.
Sodium forms the cation \(\mathrm{Na^+}\), which is much smaller than its atom because it loses its outer shell.
Sulfur forms the anion \(\mathrm{S^{2-}}\), which is larger than its atom because it gains electrons, increasing electron-electron repulsion.
Therefore, sodium has the larger atomic radius, while sulfur has the larger ionic radius, so the correct answer is (D).