Chemical Bond is a chapter where a student who understands two mechanisms, transferring electrons and sharing them, can answer almost anything the exam sets. The trick is that SPM tests the same skills in a fixed set of question shapes: form a bond, draw it, and then explain a property from it. This guide sorts those shapes, with the exact move that scores each.
Type 1: Forming an ionic bond
The first type asks how an ionic bond forms between a metal and a non-metal. The mechanism is electron transfer: the metal atom loses valence electrons to become a positive ion, the non-metal atom gains them to become a negative ion, and both reach a stable noble-gas arrangement.
Worked example: Describe the formation of sodium chloride. Sodium (2.8.1) loses one electron to form Na⁺ (2.8); chlorine (2.8.7) gains that electron to form Cl⁻ (2.8.8); the oppositely charged ions attract strongly to form NaCl. For magnesium oxide, magnesium (2.8.2) transfers two electrons to oxygen (2.6), giving Mg²⁺ and O²⁻. The full process is on our formation of an ionic compound page.
Type 2: Forming a covalent bond
The mirror type asks about two non-metals, where the mechanism is electron sharing. Each atom contributes electrons to shared pairs so that both reach a stable arrangement, forming a molecule.
Worked example: Describe the bonding in a water molecule. Oxygen (2.6) needs two more electrons, and each hydrogen (1) needs one; oxygen shares one electron with each of two hydrogen atoms, forming two single covalent bonds so that oxygen attains an octet and each hydrogen a duplet. Methane forms four bonds, and carbon dioxide forms two double bonds. See our formation of a covalent compound page for more.
Type 3: Drawing the dot-and-cross diagram
Almost every bonding question includes a dot-and-cross diagram, and marks are lost on small errors. Show only the valence electrons, use dots for one atom and crosses for the other, and for covalent bonds place the shared pair clearly in the overlap.
Worked example: For MgCl₂, magnesium loses two electrons, so you draw Mg²⁺ with an empty outer shell and two separate Cl⁻ ions each with eight electrons and a single negative charge. For a covalent molecule such as Cl₂, draw the two chlorine atoms sharing one pair, each surrounded by its remaining electrons. Neatness and the correct electron count are the whole mark.
Type 4: Comparing physical properties
The highest-value type gives an ionic and a covalent (molecular) substance and asks you to compare and explain their properties. The examinable contrasts are melting point, electrical conductivity and solubility.
Worked example: Explain why sodium chloride has a much higher melting point than a covalent substance such as naphthalene. Sodium chloride is a giant ionic lattice held by strong electrostatic forces between ions, which need a lot of energy to overcome; naphthalene is made of small molecules held by weak forces between molecules, which are easily overcome. The strength of the forces is the point, always compare it explicitly.
Type 5: Explaining electrical conductivity
A sharper property type focuses on conductivity, which is a favourite discriminator. State it precisely: an ionic compound does not conduct when solid (the ions are fixed in the lattice) but conducts when molten or in aqueous solution (the ions become free to move). A covalent compound does not conduct in any state because it has no free-moving ions or electrons.
Worked example: Explain why solid lead(II) bromide does not conduct electricity but molten lead(II) bromide does. In the solid the ions are held in fixed positions; when molten, the ions are free to move and carry charge. Tying conductivity to the freedom of the ions is what earns full marks.
Type 6: Deducing a formula from ions
A quick type gives ion charges and asks for the compound’s formula, using the rule that the total positive charge must balance the total negative charge.
Worked example: Deduce the formula of calcium chloride. Calcium forms Ca²⁺ and chloride forms Cl⁻, so two chloride ions balance one calcium ion, giving CaCl₂. Balancing the charges, not guessing, is the reliable method here.
Revising across the six
The efficient plan is to practise each move once: form an ionic bond, form a covalent bond, draw a clean dot-and-cross, compare melting points with the strength of forces, explain conductivity with the freedom of ions, and balance charges into a formula. That is how our online one-to-one lessons drill this chapter, in English from RM50 an hour with a paid one-hour trial, see how it works. Anchor every answer to electron transfer or sharing, and Chemical Bond becomes one of the most dependable chapters you have.
Ready for one-to-one help?
An experienced teacher can help your child put this into practice.
from RM50/hr · One-hour paid trial · Same-day reply