WASSCE SHS
Ionic bonding is the transfer of electrons. Covalent bonding is the sharing of electrons. The type of bond helps explain melting point and conductivity.
A metal atom can lose one or more outer electrons and become a positive ion. A non metal atom can gain those electrons and become a negative ion. The attraction between the opposite charges is the ionic bond. Sodium chloride is the standard example: sodium ions and chloride ions in a giant lattice. The lattice is strong, so the melting point is high. Solid sodium chloride does not conduct, because the ions cannot move. Melted, or dissolved in water, the ions move and it conducts.
A covalent bond is a shared pair of electrons, usually between non metal atoms. In a simple molecule such as water or chlorine, the bonds inside the molecule are strong and the forces between molecules are weak, so the melting point is low and the liquid does not conduct. Do not say every covalent substance melts easily. Diamond is covalent and giant, and it does not. If the question says "simple covalent", talk about molecules. If it says "giant covalent", talk about a network.
Transfer versus sharing is the definition mark. Properties must follow. High melting point for sodium chloride because of the strong ionic lattice, not "because it is a salt" with no reason. Conductivity needs the state: solid ionic compounds do not conduct. Simple molecular substances do not conduct in the liquid either, because there are no mobile ions or electrons. Giant covalent is the exception you mention only when the substance is one, such as diamond or graphite. Graphite conducts along the layers. Diamond does not. Do not treat them as the same.
These are practice questions in the style of the paper, with a model answer and a mark scheme. They are not a promise of what your paper will ask.
3 marks
(a) State how an ionic bond is formed. (2 marks)
(b) State how a covalent bond is formed. (1 mark)
(a) Electrons are transferred from a metal atom to a non metal atom, and the ions that form attract each other.
(b) A pair of electrons is shared between two atoms.
3 marks
Explain why solid sodium chloride does not conduct electricity, but molten sodium chloride does. (3 marks)
The solid contains ions, but they are fixed in the lattice and cannot carry charge. When the solid melts, the ions are free to move, so the melt conducts.
3 marks
Water is a simple covalent substance. State two physical properties you would expect, and give a reason for one of them. (3 marks)
A low melting point, and it does not conduct electricity. The forces between the molecules are weak, so little energy is needed to separate them.
More questions on this topic are inside GLearn, marked as you answer, with the reason written out. The first ones need no account.
Practise Chemistry freeIonic bonding transfers electrons and forms ions that attract. Covalent bonding shares a pair of electrons. Sodium chloride is ionic. Water and chlorine molecules are simple covalent substances.
Both contain ions. In the solid the ions are locked in the lattice. In the melt they can move and carry the current. Simple covalent liquids do not conduct, because they have no ions to move. All WASSCE Chemistry past questions