The table shows the type of bonding in three substances:
| Substance | Type of bonding |
|---|---|
| Chlorine, Cl2\text{Cl}_2Cl2 | simple molecular (covalent) |
| Magnesium oxide, MgO\text{MgO}MgO | ionic |
| Silicon dioxide, SiO2\text{SiO}_2SiO2 | 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.[3]
Aluminium is a lightweight metal element. Metal elements can be mixed with other metallic elements to form alloys.
Explain why a metal alloy is harder than a pure metal element.
c.
[3]
In medicine, aluminium alloys are sometimes used to make orthopedic bone plates for fixing fractures. The table shows some properties of three aluminium-based alloys.
| Alloy | Density (g/cm3\text{g/cm}^3g/cm3) | Tensile strength (MPa\text{MPa}MPa) | Contains toxic elements? |
|---|---|---|---|
| A | 2.70 | 310 | yes |
| B | 2.81 | 480 | no |
| C | 4.50 | 480 | no |
Which alloy would be best to use for a bone plate? Explain your answer.