A checklist of the mistakes that most often cost marks in Form 4 Chemical Bond, from confusing electron transfer with sharing and forgetting lone pairs and charges, to explaining melting point or conductivity without naming the structure and force, each shown with the correct version.
Every mistake below is one our teachers see often in Chemical Bond answers. For each, we show what students write, why it loses marks, and the version that scores. Read them beside your own past answers and dot-and-cross diagrams.
Standard 5.1, Why atoms bond
1. “Atoms bond to become full.” This is too vague to score. Why it loses marks: it does not say what “full” means or why it matters. Correct version: atoms bond to achieve a stable electron arrangement like that of the nearest noble gas, a full outer shell (an octet, or a duplet for the smallest atoms).
2. Giving every atom an octet, including hydrogen and helium. Why it loses marks: hydrogen and helium are stable with a duplet (2 electrons), not 8. Writing 8 electrons around hydrogen is wrong. Correct version: hydrogen reaches stability with 2 electrons; the octet rule applies to the larger atoms.
3. Saying noble gases bond to become stable. Why it loses marks: Group 18 gases already have a full outer shell, so they are unreactive and do not normally bond. Correct version: other atoms bond because they are trying to reach the arrangement noble gases already have.
Standard 5.2, The ionic bond
4. Saying the metal “shares” electrons. Why it loses marks: ionic bonding is transfer, not sharing. Using “share” describes covalent bonding and contradicts the whole idea. Correct version: the metal transfers (loses) electrons to the non-metal, forming ions.
5. Leaving charges and brackets off ions in a dot-and-cross diagram. Why it loses marks: an ion without its charge looks like a neutral atom, so the diagram does not show that a bond formed. Correct version: draw square brackets around each ion and write the charge outside, e.g. [Na]⁺ and [ :Cl: ]⁻.
6. Getting the ion ratio wrong, e.g. writing MgCl or Na O. Why it loses marks: the charges do not balance. Correct version: balance total positive and negative charge, Mg²⁺ with two Cl⁻ gives MgCl₂; two Na⁺ with one O²⁻ gives Na₂O.
7. Describing the transfer but never naming the bond. Why it loses marks: the question asks how the bond forms; transfer alone is incomplete. Correct version: add that the oppositely charged ions are held by strong electrostatic forces of attraction, that attraction is the ionic bond.
Standard 5.3, The covalent bond
8. Forgetting the lone pairs. Why it loses marks: a diagram of H₂O, NH₃, O₂ or N₂ is incomplete without the unshared pairs, and each atom will not appear to have its octet. Correct version: draw the bonding pairs in the overlap and every lone pair.
9. Using single bonds where double or triple bonds are needed. Why it loses marks: single bonds in O₂, CO₂ or N₂ leave atoms short of an octet. Correct version: O₂ has a double bond, N₂ a triple bond, and CO₂ has a double bond on each side (O=C=O).
10. Drawing brackets and charges on a covalent molecule. Why it loses marks: a simple covalent molecule such as CH₄ or H₂O is neutral, it has no overall charge and no brackets. Correct version: show only shared and lone pairs; save brackets and charges for ions.
Standard 5.4, Dative and hydrogen bonds
11. Saying H⁺ brings an electron to the dative bond. Why it loses marks: H⁺ has no electrons at all. Correct version: in NH₄⁺ or H₃O⁺, both electrons of the new bond come from the lone pair on nitrogen or oxygen, that is what makes it a dative bond.
12. Treating a hydrogen bond as a bond inside a molecule. Why it loses marks: a hydrogen bond is a weak attraction between molecules, not a covalent bond within one. Correct version: describe it as an intermolecular attraction between a hydrogen (bonded to F, O or N) and a lone pair on a neighbouring molecule.
Standard 5.5, Properties from bonding
13. Saying covalent bonds break when a molecular solid melts. Why it loses marks: melting a simple molecular solid only overcomes the weak forces between molecules; the strong covalent bonds inside each molecule stay intact. Correct version: the low melting point is due to weak intermolecular forces being easily overcome.
14. Saying an ionic solid conducts, or that electrons carry the charge. Why it loses marks: a solid ionic compound does not conduct because its ions are fixed; and it is ions, not electrons, that carry charge. Correct version: an ionic compound conducts only when molten or in aqueous solution, where the ions are free to move.
15. Explaining a property with “strong forces” but no name. Why it loses marks: “strong forces” is not specific enough for the mark. Correct version: name the exact force and structure, “strong electrostatic forces of attraction between oppositely charged ions in the giant ionic lattice.”
More slips worth catching
16. Calling a bond between two non-metals “ionic”. Why it loses marks: ionic bonding needs a metal and a non-metal so that one can lose and the other gain electrons. Two non-metals cannot both lose electrons. Correct version: two non-metals form a covalent bond by sharing electrons; a metal with a non-metal forms an ionic bond.
17. Confusing “molecule”, “compound” and “ion”. Why it loses marks: using the wrong word makes the answer imprecise, for example calling NaCl a “molecule”. Correct version: NaCl is an ionic compound made of ions in a lattice, not molecules; CO₂ is a molecule; Na⁺ is an ion. Match the word to the structure.
18. Reversing the solubility rule. Why it loses marks: writing that ionic compounds dissolve in organic solvents and covalent ones in water is the wrong way round for the common cases. Correct version: ionic compounds generally dissolve in water; many simple covalent compounds dissolve in organic solvents, “like dissolves like”.
19. Saying a bigger charge always means a higher melting point, with no reasoning. Why it loses marks: a bare claim with no mechanism does not score. Correct version: explain that ions with higher charges attract more strongly, so more energy is needed to separate them and the melting point is higher, the reasoning carries the mark, not the claim.
How to use this list
Work through the checklist after each set of practice questions and tick which mistakes you tend to make. Most students lose marks in two or three predictable places, usually missing lone pairs, missing charges, or a property answer without a named force. Fixing those few habits lifts your bonding marks quickly. A one-to-one teacher can mark your dot-and-cross diagrams against this list and point out exactly which of these slips is costing you marks across the SPM Chemistry papers.
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