Chlorine reacts with sodium to form sodium chloride.
What happens to the sodium atoms during this reaction?
A) They gain electrons to form anions.
B) They lose electrons to form anions.
C) They gain electrons to form cations.
D) They lose electrons to form cations.
▶️ Answer/Explanation
Ans: D
Sodium is a Group 1 metal that readily loses its single valence electron to achieve a stable noble gas configuration.
In the reaction:
- Sodium atoms lose 1 electron each (oxidation) to become Na⁺ cations
- Chlorine atoms gain 1 electron each (reduction) to become Cl⁻ anions
Key points:
- Metals lose electrons to form positive ions (cations)
- Anions are negative ions formed by gaining electrons
- Sodium would never gain electrons as it’s already electron-deficient being a metal
Nitrogen monoxide, NO, is a simple molecular compound.
Which row shows the properties of nitrogen monoxide?
| boiling point | electrical conductivity | |
|---|---|---|
| A | high | good |
| B | high | poor |
| C | low | good |
| D | low | poor |
▶️ Answer/Explanation
Ans: D
Nitrogen monoxide (NO) is a simple molecular compound, which means:
- It has low boiling point because the intermolecular forces (van der Waals forces) between molecules are weak.
- It has poor electrical conductivity because it doesn’t contain free electrons or ions to carry charge.
Simple molecular compounds typically have these characteristics because they consist of small, discrete molecules with covalent bonds within the molecules but only weak forces between them.
Covalent bonds are formed when electrons are ……1…… .
Most covalent compounds have ……2…… electrical conductivity.
Which words correctly complete gaps 1 and 2?
| 1 | 2 | |
|---|---|---|
| A | shared | high |
| B | shared | low |
| C | transferred | high |
| D | transferred | low |
▶️ Answer/Explanation
Ans: B
Covalent bonds are formed by the sharing of electrons between atoms, not by transferring electrons (which is characteristic of ionic bonds).
Most covalent compounds have low electrical conductivity because:
- They don’t have free electrons or ions to carry charge
- They are typically molecular compounds that don’t ionize in solution
Exceptions include some covalent network structures like graphite, but the question specifies “most” covalent compounds.
Which row gives the number of covalent bonds in one molecule of ammonia and in one molecule of hydrogen chloride?
| ammonia | hydrogen chloride | |
|---|---|---|
| A | 3 | 1 |
| B | 3 | 2 |
| C | 4 | 1 |
| D | 4 | 2 |
▶️ Answer/Explanation
Ans: A
Ammonia (NH₃) has 3 covalent bonds – one between nitrogen and each hydrogen atom. Nitrogen has 5 valence electrons and forms 3 single bonds, leaving one lone pair.
Hydrogen chloride (HCl) has just 1 covalent bond between the hydrogen and chlorine atoms. Hydrogen can only form one bond, and chlorine needs just one more electron to complete its outer shell.
Therefore, the correct combination is 3 bonds in ammonia and 1 bond in hydrogen chloride.