NCEA 91164: bonding, structure, properties and energy changes (Level 2 Chemistry)

What NCEA 91164 assesses

NZQA says bonding, structure and energy changes in the standard (version 2) are limited to:

• ionic, covalent and metallic bonding, and intermolecular forces (you do not need to tell the types apart)
• Lewis structures, shape and polarity of simple molecules, with no more than four electron pairs about any atom
• molecular, ionic, metallic and covalent network substances
• exothermic and endothermic reactions, including enthalpy changes for different amounts of substance, changes of state, and making and breaking bonds
• calculations of energy changes using ΔrH and reaction stoichiometry, and bond enthalpy
• properties limited to hardness, malleability, ductility, electrical conductivity, melting and boiling points and solubility

The three grades go up in steps. Achieved describes, identifies, names, draws, calculates or gives an account of bonding, structure and properties and the energy involved in physical and chemical changes. Merit makes and explains links between the bonding, structure and properties of different substances and the energy involved. Excellence elaborates, justifies, relates, evaluates, compares and contrasts, or analyses those links. Every grade needs correct chemistry vocabulary, symbols and conventions, and Excellence needs them used consistently.

The NCEA 91164 exam in 2026 and 2027

NCEA 91164 is one of three Level 2 Chemistry externals, with 91165 (organic compounds) and 91166 (chemical reactivity). The 2026 exam is on Monday 16 November, in the afternoon session. NZQA's specifications for both years say the exam is on printed paper and 91164 is a 5-credit external.

• Three questions: you answer all three, and each has several parts. Questions may be set in contexts that are unfamiliar to you, and any context-specific formulae are given in the exam.
• Calculator: an approved scientific or graphics calculator is required.
• Resource booklet: it has the formulae you need, such as n = cV, and a periodic table with element symbols, atomic numbers and molar masses. Use the molar masses given with the question or on the periodic table.
• Calculations: show all working, round numerical answers to three significant figures and include the correct units.
• Conventions: symbols, nomenclature, spelling and formatting follow IUPAC conventions. The reference sheet for these is not provided in the exam.
• Solubility: NZQA says solubility in this standard refers to polar and non-polar solvents.

How NCEA 91164 is marked

Three questions are each scored N0 to E8 and added to a total out of 24. NZQA's report says the three questions asked you to link bonding, structure and properties and the energy involved, so a good answer names the particle type and the force before it mentions a property.

NCEA 91164 cut scores

This standard has the steadiest boundaries of the Level 2 chemistry externals: 8, 14 and 19 in all five years. The scores are where each grade begins, out of 24.

Cut scores 2025

2025 schedule: Achieved from 8, Merit from 14, Excellence from 19. The same as 2024.

Cut scores 2024

2024 schedule: Achieved from 8, Merit from 14, Excellence from 19. The same as 2023.

Cut scores 2023

2023 schedule: Achieved from 8, Merit from 14, Excellence from 19. The same as 2022.

Cut scores 2022

2022 schedule: Achieved from 8, Merit from 14, Excellence from 19. The same as 2021.

Cut scores 2021

2021 schedule: Achieved from 8, Merit from 14, Excellence from 19.

Worked examples at each grade

Achieved: shape and polarity

Give the shape of NH₃ and CO₂ and say whether each is polar. In ammonia, nitrogen uses three pairs to bond and keeps one non-bonding pair, so there are four regions of electron density, and the shape is trigonal pyramidal. The N-H bonds are polar and the shape is not symmetrical, so the bond dipoles do not cancel and NH₃ is polar. Carbon dioxide has two regions of electron density, so it is linear. The C=O bonds are polar, but they point in opposite directions and cancel, so CO₂ is non-polar.

Merit: linking structure to properties

Explain why solid magnesium conducts electricity but solid magnesium chloride does not, although molten magnesium chloride does. Magnesium is a metal: its atoms are held by attraction between the cations and a sea of delocalised electrons, and those electrons are free to move, so solid magnesium conducts. Magnesium chloride is an ionic lattice. In the solid, the ions sit in fixed places, so there are no mobile charged particles. On melting, the ions can move, so they carry charge through the liquid. NZQA's 2025 report says that conductivity needs mobile charged particles, and that attributing it only to mobile electrons was a common mistake.

The same ideas explain malleability. In a metal the bonding is non-directional, so layers of cations slide over each other and the lattice stays together. In an ionic crystal a shift of a layer brings like charges together, and the crystal breaks.

Excellence: energy calculations and a justified comparison

Take the equation 2H₂(g) + O₂(g) → 2H₂O(l), with ΔrH = −572 kJ for the equation as written. How much energy is released when 10.0 g of hydrogen burns? The molar mass of H₂ is 2.0 g mol⁻¹:

Now a bond enthalpy calculation, using the values given in a question (H-H 436, Br-Br 193 and H-Br 366 kJ mol⁻¹) for H₂ + Br₂ → 2HBr. Bonds broken take in energy and bonds formed release it:

The negative sign means the reaction is exothermic. NZQA's 2025 report says Excellence candidates gave correct signs, units and three significant figures. A justified comparison is the other half of Excellence. Why does diamond melt at a much higher temperature than iodine? Diamond is a covalent network: melting it means breaking strong covalent bonds throughout a 3D lattice, which takes a great deal of energy. Iodine is molecular: melting only overcomes weak intermolecular forces between molecules, and the covalent bonds inside each I₂ molecule stay intact. Use comparative language: "much stronger", "more energy".

Now work out the energy needed to break bonds in our Chemical Bonding course, then press Mark to check your answer in the course:

Exam answers

The answers and a worked mark scheme come with today's paper once it is marked. We do not publish official or past paper answers. Every question on the daily paper is our own.

Use the daily paper as a practice exam

The Level 2 Chemistry track above is a short timed mock of 8 questions, not a full exam and not written by NZQA (NCEA Level 2 Chemistry). It covers bonding and the shapes of molecules, intermolecular forces, and enthalpy changes, which support 91164. It also includes amounts of substance, redox, kinetics and periodicity, which belong to other standards or to a higher level, so treat those as extra. For the whole course, see the NCEA Level 2 Chemistry guide.

Is NCEA 91164 changing?

NZQA's 2027 chemistry specification repeats the 2026 notes for this standard, including that solubility means polar and non-polar solvents. Year 12 moves to the NZ Certificate of Education in 2029.

Common mistakes in NCEA 91164

• Using "particle" as a catch-all. NZQA's 2025 report says Not Achieved candidates did not name the type of particle: atom, ion or molecule.
• Missing that diamond is a 3D covalent network. Describe the structure, not just the word "strong".
• Calling NaCl a polar molecule. It is an ionic lattice with no molecules, and the report lists this error.
• Explaining malleability without non-directional bonding. Metal cations or atoms can slide over each other.
• Wrong signs or units. Give +/− on enthalpy changes, units, and three significant figures.
• Not comparing. At Merit and above, relate the ideas to the examples in the question and say what is similar and what is different.

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