Question

Phosphate, PO43- is an oxyanion.

     Deduce the formula of calcium phosphate.                                                               [1]

 

 

1.7 Sulfur combines with carbon to give carbon disulfide, CS2.

      Draw a ‘dot-and-cross’ diagram of the carbon disulfide molecule.

      Show outer electrons only.                                                 

Answer 1

### Part 1: Formula of Calcium Phosphate

Calcium (Ca) has a charge of +2, and the phosphate ion (PO₄³⁻) has a charge of -3. To form a neutral compound, we need to balance the charges by adjusting the ratio of calcium to phosphate.

- To balance +2 from calcium and -3 from phosphate, we use the least common multiple of the charges, which is 6.
- Therefore, we need three calcium ions (3 × +2 = +6) and two phosphate ions (2 × -3 = -6).

Thus, the formula for calcium phosphate is **Ca₃(PO₄)₂**.

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### Part 2: Dot-and-Cross Diagram of Carbon Disulfide (CS₂)

To draw the dot-and-cross diagram for carbon disulfide (CS₂), you represent the outer electrons of each atom with distinct dots and crosses.

1. **Carbon (C)** has 4 outer electrons.
2. **Sulfur (S)** has 6 outer electrons, and there are two sulfur atoms.

The bonding involves the carbon atom sharing its electrons with both sulfur atoms.

**Diagram:**

```
S S
•• ••
| \ / |
| •• •• |
| C |
| •• •• |
| / \ |
•• ••
```

Where:
- “C” is at the center representing the carbon atom.
- The “••” around the sulfur atoms represent the outer electrons of sulfur.
- The lines (or pairs of dots) between carbon and sulfur illustrate the shared electrons (covalent bonds).

In this case, each sulfur shares two of its electrons with carbon, resulting in double bonds between carbon and both sulfur atoms.

**Note:** In the diagram, the dots correspond to electrons from carbon, and crosses correspond to electrons from sulfur.