Which statement explains why sodium and potassium have different melting points?
Correct Answer: \( \boxed{\mathrm{A}} \)
Sodium and potassium are metals with metallic bonding.
Metallic bonding is the electrostatic attraction between positive metal ions (cations) and delocalised electrons.
Sodium ions are smaller than potassium ions, so the attraction between the cations and the delocalised electrons is stronger in sodium.
Therefore, sodium has a higher melting point, and the correct answer is (A).
Why does \(\mathrm{ICl}\) have a higher boiling point than \(\mathrm{Br_2}\)?
Correct Answer: \( \boxed{\mathrm{B}} \)
Both \(\mathrm{ICl}\) and \(\mathrm{Br_2}\) have similar relative molecular masses and therefore similar London dispersion forces.
However, \(\mathrm{ICl}\) is a polar molecule because chlorine is more electronegative than iodine. As a result, \(\mathrm{ICl}\) molecules experience permanent dipole-dipole attractions in addition to London dispersion forces.
In contrast, \(\mathrm{Br_2}\) is a non-polar molecule and has only London dispersion forces between its molecules.
Therefore, the correct answer is (B).
The diagram shows part of the lattice structures of solids X and Y.
What are the types of bonding present in X and Y?
| X | Y | |
|---|---|---|
| A | covalent | metallic |
| B | ionic | covalent |
| C | ionic | metallic |
| D | metallic | ionic |
Correct Answer: \( \boxed{\mathrm{B}} \)
Solid X shows a regular three-dimensional lattice containing two different types of particles arranged alternately, which is characteristic of a giant ionic lattice.
Solid Y consists of layers of hexagonally arranged atoms, similar to graphite. Each layer is held together by strong covalent bonds, with weak forces between the layers.
Therefore, the correct answer is (B).
