What does the particle model assume about the particles that make up a substance?

It assumes that all substances are made of tiny particles that are constantly moving and are attracted to one another.

Describe the arrangement and movement of the particles in a solid.

They are packed closely together in a regular arrangement and vibrate about fixed positions.

Describe the arrangement and movement of the particles in a liquid.

They are still close together but arranged randomly, and they move around and slide past one another.

Describe the arrangement and movement of the particles in a gas.

They are far apart and arranged randomly, and they move quickly in all directions.

Name the change of state in which a liquid becomes a gas, and the reverse change.

A liquid becoming a gas is boiling or evaporating, and a gas becoming a liquid is condensing.

OCR GCSE Combined Science Chemistry J250

Chemical Reactions

Topic overview Writing formulae of elements and compounds Balanced equations, and deducing formulae from ions Ionic equations, and state symbols The mole and the Avogadro constant Conservation of mass, and changes of mass in open systems Stoichiometry, and calculating reacting masses Exothermic and endothermic reactions, and reaction profiles Activation energy, and bond energy calculations Oxidation and reduction, by oxygen and by electrons Acids, alkalis and neutralisation The ionic equation for neutralisation, and reactions of acids Dilute and concentrated, weak and strong The pH scale, and hydrogen ion concentration pH as a factor of ten, and measuring pH Products at the electrodes, and molten ionic compounds Electrolysis of aqueous solutions Inert and non-inert electrodes

Elements, Compounds and Mixtures

Topic overview Purity, and melting point data Relative formula mass and empirical formulae Formulations, and separating mixtures Paper and thin layer chromatography Interpreting chromatograms and Rf values Choosing a purification method Metals and non-metals in the Periodic Table Electron arrangement and position in the Periodic Table Ionic, covalent and metallic bonding compared Dot and cross diagrams, and the limits of models Reactions, electron arrangement and Mendeleev's table Carbon's four bonds, and the variety of organic compounds Diamond, graphite, fullerenes and graphene Bond strength, intermolecular forces and predicting state Bulk properties of ionic, molecular and giant structures

Global Challenges

Topic overview Extracting metals by reduction and by electrolysis Biological methods of metal extraction Life cycle assessment Recycling, and the decisions behind it Fractional distillation of crude oil The fractions, and crude oil as a feedstock Dependence on hydrocarbons, and cracking The Earth's early atmosphere, and how oxygen developed The greenhouse effect, and evidence for climate change Effects of carbon dioxide and methane, and air pollutants Producing potable water

Monitoring and Controlling Chemical Reactions

Topic overview Mass of solute, concentration and dilution calculations Measuring the rate of a reaction, and rate graphs Factors affecting rate, and collision theory Surface area and rate Catalysts and how they work Reversible reactions and dynamic equilibrium Changing the conditions of an equilibrium Activation energy, and enzymes as catalysts

Particles

Topic overview The particle model and changes of state Limitations of the particle model How the atomic model changed, and the structure of the atom The size of atoms, and the subatomic particles Calculating protons, neutrons and electrons

Predicting and Identifying Reactions

Topic overview Groups 1, 7 and 0, and why they behave as they do Predicting reactivity from the Periodic Table Reactivity of metals with water and acids Tests for oxygen, hydrogen, carbon dioxide and chlorine

Particles

The particle model and changes of state

3 things to know
Paper 9 (Chemistry)

Overview

What the particle model assumes, the arrangement and movement of particles in solids, liquids and gases, melting, freezing, boiling, condensing and sublimation, why melting needs energy and gases compress, what physical and chemical changes are and how to tell them apart, why melting, freezing and dissolving salt are physical while burning magnesium is chemical, and why physical changes reverse easily.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Define a physical change and a chemical change, and explain in terms of the particle model why melting counts as physical.

Key term

Name the changes of state between solid, liquid and gas, and explain why a gas can be compressed but a solid cannot.

Key term

Name the change of state in which a solid becomes a liquid, and the reverse change.

Questions from this subtopic

Each one with the model answer underneath.

1
What does the particle model assume about the particles that make up a substance?
Model answer
It assumes that all substances are made of tiny particles that are constantly moving and are attracted to one another.
2
Describe the arrangement and movement of the particles in a solid.
Model answer
They are packed closely together in a regular arrangement and vibrate about fixed positions.
3
Describe the arrangement and movement of the particles in a liquid.
Model answer
They are still close together but arranged randomly, and they move around and slide past one another.
4
Describe the arrangement and movement of the particles in a gas.
Model answer
They are far apart and arranged randomly, and they move quickly in all directions.
5
Name the change of state in which a solid becomes a liquid, and the reverse change.
Model answer
A solid becoming a liquid is melting, and a liquid becoming a solid is freezing.
6
Name the change of state in which a liquid becomes a gas, and the reverse change.
Model answer
A liquid becoming a gas is boiling or evaporating, and a gas becoming a liquid is condensing.

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Chemical Reactions

Elements, Compounds and Mixtures

Global Challenges

Monitoring and Controlling Chemical Reactions

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BKI, because potassium loses one electron and iodine gains one.

CCaCl₂, because a calcium atom loses two electrons and each chlorine atom gains one.

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