The table shows the type of bonding in three substances:
| Substance | Type of bonding |
|---|---|
| Nitrogen, N2\text{N}_2N2 | simple molecular (covalent) |
| Sodium chloride, NaCl\text{NaCl}NaCl | ionic |
| Diamond, C\text{C}C | giant covalent |
a.[4]
Describe and compare the types of bonding in these three substances. Predict which substance will have the lowest melting point.
b.[2]
Titanium is a strong transition metal. Metallic elements can be mixed with other elements to form alloys.
Explain why a metal alloy is harder than a pure metal element.
c.
[3]
In aerospace engineering, titanium-based alloys are often used to manufacture compressor blades for jet engines.
The table shows some properties of three titanium-based alloys.
| Alloy | Density (g/cm3\text{g/cm}^3g/cm3) | Tensile strength (MPa\text{MPa}MPa) | Operating temperature limit (∘C^\circ\text{C}∘C) |
|---|---|---|---|
| X | 4.50 | 950 | 500 |
| Y | 4.43 | 1100 | 900 |
| Z | 5.80 | 1100 | 900 |
If the engine compressor blades are designed to operate at a temperature of 800∘C800^\circ\text{C}800∘C, which alloy would be best to use? Explain your answer.