1. Chem HL 1.1 Intro to particulate nature of matter

Define an element

A pure substance consisting of only one type of atom, cannot be broken down chemically.

Define a compound

A pure substance is formed when two or more elements are chemically bonded in fixed ratios

Define a mixture

A combination of two or more substances not chemically bonded in variable ratios

What is a molecule

Two or more atoms either same or different elements that are covalently bonded together

Uniform and Non-uniform meaning

Uniform - homogeneous, components distributed evenly

Non-uniform - heterogeneous, components not evenly distributed

Differentiate between a homogeneous and a heterogeneous mixture with an example each

Homogeneous, uniform composition and appears as a single phase e.g., salt water

Heterogeneous, non-uniform composition and appears as different phases e.g. oil and water

What is a lattice

A fixed, repeating pattern or arrangement of points in space - a highly ordered 3-dimensional arrangement

Describe the arrangement of particles in a solid

fixed position in the lattice, vibrating particles, but don't move freely.

Describe the arrangement of particles in a liquid.

Particles are close together, but free to move past each other

Describe the arrangement of particles in a gas.

Far apart, particles are moving randomly and at high speeds

What is sublimation, give 2 examples

Direct change from solid to gas without a liquid phase. e.g., CO2, dry ice, iodine

What is a physical change?

A change in state without altering chemical composition, e.g., melting

What is a chemical change?

A change that results in a new substance being formed e.g., rusting and combustion

How can you distinguish a chemical change from a physical one?

Chemical involves bond breaking/forming, often with energy changes, colour change, gas releas,e or precipitate

How can a mixture of sand and salt be separated

Dissolve salt in water, filter sand, evaporate water from salt soltuion

What technique separates liquids based on boiling points?

Distillation - vapourising the liquid with a higher boiling point, then condensing it.

What technique separates pigments in ink?

Chromatography - by separating a mixture's components based on their differing affinities for a stationary phase and a mobile phase.

What technique separates an insoluble solid from a liquid?

Filtration

Affinity meaning

The force of attraction or the tendency of substances to combine and form chemical bonds, leading to stable compounds

What is the difference between an atom and an ion?

Atom = neutral

Ion = charged due to loss or gain of electrons

What is the difference between an element and a compound at the particulate level?

Element = 1 type of atom

Compound = chemically bonded atoms of different elements

Why can mixtures be separated by physical methods but compounds cannot?

mixtures are not chemically bonded; compounds are

Why is CO considered a compound but O₂ a molecule?

CO has different elements chemically bonded; O2 has two identical atoms bonded.

What does atom economy tell us?

If the product produced is:

- more efficient/economically efficient

- if it is sustainable development (less inefficient ratio of product vs reactants)

- better use of natural resources

- reduces waste