Chemistry NCEA L1 AS92023 - UNDERSTANDING

What does 92023 require you to explain?

How the physical properties of materials inform their use by linking properties to particle arrangement and the relative strength of attractive forces between particles.

What is the basic chain you should use in an answer?

Structure/particles → attractive forces or bonding → physical property → why the property makes the material suitable for its use.

What is the difference between Achievement, Merit and Excellence?

Achievement describes properties and use; Merit explains by linking properties to structure or bonding; Excellence evaluates by linking properties to both structure and attractive forces/bonding.

Why is particle arrangement important?

The arrangement and movement of particles affects the physical properties of a material.

Why are attractive forces important?

The strength of attractions between particles affects how easily particles can move or separate, influencing properties such as melting point, hardness and conductivity.

What are the five material types in 92023?

Molecular substances, metallic solids, ionic materials, natural and synthetic polymers, and covalent networks.

What are examples of molecular substances?

Water and iodine.

What are examples of metallic solids?

Lead pipe, magnesium alloy wheels, and copper wire.

What are examples of ionic materials?

Nitrate fertilisers and salt.

What are examples of polymers?

DNA, proteins, and non-stick coatings on cookware.

What are examples of covalent networks?

Diamond and graphite.

What are the particles in molecular substances?

Molecules.

What holds atoms together within a molecule?

Strong covalent bonds.

What holds separate molecules together?

Intermolecular forces.

Why do molecular substances often have relatively low melting and boiling points?

The forces between molecules are generally weaker than the covalent bonds within the molecules, so less energy is needed to separate the molecules.

Why does a molecular substance remain a molecule when it melts?

The intermolecular forces are overcome, but the covalent bonds within each molecule remain intact.

What happens to molecular substances when they dissolve?

Interactions between the solvent and molecules allow the molecules to separate and become dispersed through the solvent.

What particles make up a metallic solid?

Positive metal ions and delocalised electrons.

Why do metals conduct electricity?

Their delocalised electrons can move through the structure and carry electrical charge.

Why do metals conduct thermal energy?

Delocalised electrons can transfer energy through the structure efficiently.

Why are metals malleable?

Layers of metal ions can slide past one another while the metallic bonding remains because the delocalised electrons continue attracting the ions.

Why are metals generally strong?

Strong metallic bonding holds the positive metal ions and delocalised electrons together.

What happens when a metal is bent?

Layers of metal ions can move relative to each other without the structure completely breaking.

What particles make up an ionic material?

Positive and negative ions arranged in a repeating lattice.

Why are ionic materials often hard?

Strong electrostatic attractions hold oppositely charged ions in a rigid lattice.

Why do ionic solids have high melting points?

Strong electrostatic attractions between oppositely charged ions require a large amount of energy to overcome.

Why don't solid ionic materials conduct electricity?

The ions are fixed in position and cannot move through the solid to carry charge.

Why can molten ionic materials conduct electricity?

The ions are free to move when the lattice has been disrupted by melting.

Why can aqueous ionic substances conduct electricity?

The ions are separated and mobile in the solution.

Why are ionic materials often brittle?

If layers shift, similarly charged ions can become aligned, causing strong repulsion and the lattice to fracture.

What happens when an ionic material dissolves in water?

Water molecules interact with the ions and separate them from the lattice so the ions become dispersed and mobile.

What particles make up a covalent network?

Atoms joined by strong covalent bonds in a continuous network.

Why are covalent networks generally hard?

Strong covalent bonds connect atoms throughout the entire structure, making the network difficult to deform.

Why do covalent networks generally have high melting points?

A large number of strong covalent bonds must be broken to melt the structure.

Why is diamond very hard?

Each carbon atom is strongly covalently bonded to other carbon atoms in a rigid three-dimensional network.

Why doesn't diamond conduct electricity?

All of its outer electrons are involved in covalent bonds, so there are no mobile electrons available to carry charge.

Why does graphite conduct electricity?

Graphite has delocalised electrons that can move through its layers and carry electrical charge.

Why is graphite softer than diamond?

Graphite has strong covalent bonds within layers but much weaker attractions between layers, allowing the layers to slide over one another.

What are the particles in a polymer?

Very large molecules made from repeating units.

Why can polymers have different physical properties?

Different polymer structures, chain arrangements and attractive forces produce different properties.

Why can some polymers be flexible?

Their long chains can move or slide relative to one another, depending on their structure and intermolecular forces.

Why can some polymers be strong?

Strong attractions between polymer chains or cross-links can restrict chain movement and increase strength.

Why are some polymers good electrical insulators?

They generally do not have freely moving charged particles or delocalised electrons.

Why are polymers useful for non-stick coatings?

Their surface properties can reduce interactions with other substances, helping food and other materials resist sticking.

Why does structure determine physical properties?

The arrangement of particles and the strength of attractions determine how easily particles can move, separate or conduct energy and charge.

Why does stronger attraction generally mean a higher melting point?

More energy is required to overcome stronger attractions between particles.

Why does particle mobility matter for electrical conductivity?

Charge must be able to move through the material for electrical current to flow.

Why does the type of bonding matter when choosing a material?

Different bonding and particle arrangements produce different physical properties, making materials suitable for different purposes.