Ionic compounds generally have:

Ionic compounds are compounds formed by the transfer of electrons from one atom to another, usually from a metal to a non-metal. The atom that loses electrons becomes a positive ion (cation), and the atom that gains electrons becomes a negative ion (anion). The strong electrostatic force of attraction between oppositely charged ions is called an ionic bond or electrovalent bond. Common examples are sodium chloride (NaCl), potassium bromide (KBr), magnesium oxide (MgO) and calcium chloride (CaCl2).

In the solid state, ionic compounds form a regular, three-dimensional arrangement of ions called a crystal lattice. Each ion is surrounded by many ions of opposite charge, so the forces holding the lattice together are very strong. A lot of energy is needed to break these forces. This is why ionic compounds have high melting and boiling points. For example, sodium chloride melts at about 801°C, and magnesium oxide melts at about 2,852°C.

Other properties of ionic compounds include:

• They are usually hard, brittle crystalline solids.
• They are generally soluble in water, but insoluble in organic solvents such as kerosene and petrol.

They do not conduct electricity in the solid state, because the ions cannot move. But they conduct electricity when molten or dissolved in water, because the ions are then free to move.

Covalent compounds, formed by sharing electrons, such as methane and carbon tetrachloride, usually have low melting and boiling points, are often liquids or gases at room temperature, dissolve in organic solvents and are poor conductors of electricity.

Why not the other options?

• ✗Low melting and boiling points are typical of covalent compounds.
• ✗Ionic compounds do conduct electricity in the molten state.
• ✗Ionic compounds are generally insoluble in kerosene and other organic solvents.