AS Bonding

Water reacts with H+ ions to form H3O+ ions. Identify the bonding within the H3O+ ion.

• covalent bonding only

• covalent and dative covalent bonding only

• covalent, dative covalent and ionic bonding

• ionic bonding only

Answer explanation

In H3O+, the bonding involves covalent bonds between oxygen and hydrogen atoms. The H+ ion donates a proton to water, forming a dative covalent bond. Thus, the correct answer is covalent and dative covalent bonding only.

What are the shapes of the AlCl3 and PH3 molecules?

• AlCl3: pyramidal, PH3: pyramidal

• AlCl3: pyramidal, PH3: trigonal planar

• AlCl3: trigonal planar, PH3: trigonal planar

• AlCl3: trigonal planar, PH3: pyramidal

Answer explanation

AlCl3 has a trigonal planar shape due to its three bonding pairs and no lone pairs on the central aluminum atom. PH3 has a pyramidal shape because it has one lone pair on phosphorus, causing a bent structure.

Which describes the polarity of the C–Cl bond and the polarity of the CCl4 molecule?

• C–Cl bond: non-polar, CCl4 molecule: non-polar

• C–Cl bond: non-polar, CCl4 molecule: polar

• C–Cl bond: polar, CCl4 molecule: polar

• C–Cl bond: polar, CCl4 molecule: non-polar

Answer explanation

The C–Cl bond is polar due to the difference in electronegativity between carbon and chlorine. However, CCl4 is a symmetrical molecule, causing the dipoles to cancel out, making it non-polar.

Which of the following correctly represents the outer shell electrons in magnesium chloride (MgCl2)?

• Mg atom loses two electrons, each Cl atom gains one electron, showing Mg2+ and two Cl- ions with full outer shells.

• Mg atom shares electrons with two Cl atoms, forming covalent bonds.

• Mg atom gains two electrons from two Cl atoms, forming Mg2- and two Cl+ ions.

• Mg atom and Cl atoms do not transfer or share electrons, remaining neutral.

Answer explanation

In magnesium chloride (MgCl2), the Mg atom loses two electrons, becoming Mg2+, while each Cl atom gains one electron, forming two Cl- ions. This results in full outer shells for all ions, confirming the correct choice.

Magnesium conducts electricity in the solid state, but magnesium chloride only conducts electricity when molten or dissolved in water. What explains these observations?

• Magnesium has free electrons in the solid state, while magnesium chloride has mobile ions only when molten or dissolved.

• Both magnesium and magnesium chloride have free electrons in the solid state.

• Magnesium chloride has free electrons in the solid state, but magnesium does not.

• Magnesium and magnesium chloride both conduct electricity only when molten.

Answer explanation

Magnesium conducts electricity due to free electrons in its solid state. In contrast, magnesium chloride only conducts when molten or dissolved because it requires mobile ions to carry the electric current.

Metallic bonding is the strong electrostatic attraction between

• anions and cations

• atoms and delocalised electrons

• +ve ions and delocalised electrons

• two nuclei and a shared pair of electrons

Answer explanation

Metallic bonding occurs due to the strong electrostatic attraction between positively charged ions (cations) and delocalised electrons. This interaction allows metals to conduct electricity and exhibit malleability.

The ionic radius of Al³⁺ is smaller than that of N³⁻. This is because Al³⁺ has

• fewer protons but more electrons than N³⁻

• more protons but fewer electrons than N³⁻

• more protons than N³⁻ but the same number of electrons as N³⁻

• the same number of protons as N³⁻ but fewer electrons

Answer explanation

Al³⁺ has more protons than N³⁻ but the same number of electrons (10). The greater positive charge in Al³⁺ pulls the electrons closer to the nucleus, resulting in a smaller ionic radius compared to N³⁻.

Which ion has the greatest polarising power?

• Cl⁻

• Mg²⁺

• Na⁺

• S²⁻

Answer explanation

Mg²⁺ has the greatest polarising power due to its high charge and small size, which allows it to distort the electron cloud of nearby anions more effectively than Cl⁻, Na⁺, or S²⁻.

Which species is not tetrahedral?

• CCl₄

• CH₄

• ICl₄⁻

• NH₄⁺

Answer explanation

ICl₄⁻ has a square planar geometry due to the presence of two lone pairs on the iodine atom, making it not tetrahedral. In contrast, CCl₄, CH₄, and NH₄⁺ all have tetrahedral shapes.

A dot-and-cross diagram of a nitrogen molecule shows how many shared pairs of electrons between the two nitrogen atoms?

• Three shared pairs

• One shared pair

• Two shared pairs

• Four shared pairs

Answer explanation

A nitrogen molecule (N2) has a triple bond, which consists of three shared pairs of electrons between the two nitrogen atoms. Therefore, the correct answer is three shared pairs.