Chemical bonding TYS questions - Combined Chemistry

Answer: C is not correct

• A is correct as sodium chloride is an ionic compound made up of sodium positive ions and chloride negative ions. The oppositely charged ions attract each other.
• B is correct as most ionic compounds can dissolve in water to form aqueous solutions.
• C is wrong. Ionic compounds have a high melting point, because the electrostatic forces of attraction between the oppositely charged ions are strong. Therefore, a large amount of energy is required to overcome them.
• D is correct, as many oppositely charged ions attract one another to form a giant ionic crystal lattice.

Answer: B

STEP 1: Recall and state the charge of the common ion
Sulfate anion has a charge of 2- and hence is SO₄^2-.

STEP 2: Calculate the charge of the unfamiliar ion
A formula unit has 3 sulfate ions with a combined negative charge of 6-. To balance it, the combined positive charge must be 6+. Since there are only 2 chromium ions, each chromium ion has a positive charge of 6+ ÷ 2 = 3+.

This is a harder inference question. To do it, you need to have memorised the charges of sulfate ion, which is an ion commonly tested in the O Level. Then, you infer the charge of the unknown chromium ion.

There is no way to directly tell the charge of the chromium ion, because it is a transition metal ion that can take on different charges in different compounds.

Answer: C is not correct

• A is correct. Sodium is a metallic element that loses electron to form a positive ion. Chlorine is a non-metallic element that gains electron to form a negative ion.
• B is correct. The strong electrostatic forces of attraction between sodium cations and chloride anions require a large amount of energy at high temperature to overcome.
• C is wrong. In the solid state, the oppositely charged ions are held in fixed position by the strong electrostatic forces of attraction between them. Therefore, the ions are not mobile to conduct electricity. Instead, ionic compounds only conduct electricity in the liquid and aqueous states.
• D is correct. Sodium chloride has a giant ionic lattice structure comprising many oppositely charged ions arranged in a regular pattern.

Answer: A is not correct

• A is wrong because only the outer shell electrons are shown. Element A has at least one inner shell with 2 more electrons, as its outer shell contains 5 electrons.
• B is correct. The ‘dot-and-cross’ diagram shows a covalent compound whereby atoms share electrons. And most covalent compounds are formed between non-metallic atoms.
• C is correct. Atom A has 5 valence electrons represented by the 5 dots. Therefore, it must be from Group V.
• D is correct. Atom B has 1 valence electron represented by the 1 cross. The only non-metal with 1 valence electron is hydrogen.

Answer: B

In a covalent bond, two atoms share electrons. The atoms are non-metallic.

The most important step to answering this question is to first consider if the compound is covalent or ionic. This is hinted by the question. It tells us that sodium oxide and hydrogen sulfide have very different properties, suggesting that their structure and bonding are different.

Sodium oxide is ionic as it comprises a metallic element and a non-metallic element. In an ionic compound, the metallic element has lost its valence electrons to form positive ions while the non-metallic element has gained electrons to form negative ions. The ions formed have the noble gas electronic configuration.

However, hydrogen sulfide is covalent, as it is formed between non-metallic elements. In a covalent compound, the atoms share electrons to achieve the noble gas electronic configuration. In hydrogen sulfide, hydrogen has 2 valence electrons upon sharing, just like the noble gas helium. Sulfur has 8 valence electrons after sharing, like in the noble gas argon.

Sodium oxide has a giant ionic lattice structure. In the solid state, the ions held in fixed position are not mobile to conduct electricity.

Hydrogen sulfide has a simple molecular structure. In all states, there is no free-moving electrons or mobile ions to conduct electricity.

Sodium oxide has a giant ionic lattice structure. Upon melting, the strong electrostatic forces of attraction between oppositely charged ions are overcome, allowing the ions to be free-moving.

When something is molten, it has been melted at high temperature to form a liquid.

Carbon dioxide has a simple molecular structure. The intermolecular forces of attraction between carbon dioxide molecules are weak, such they can be overcome with a small amount of energy at a low temperature.