Explain why leaving out the forces between particles makes the model poor at explaining boiling points.

Boiling requires enough energy to overcome the attraction between the particles, so a model with no forces cannot explain why different substances boil at different temperatures.

Why is it a limitation that the model draws every particle as a sphere of the same size?

Real particles differ in size from substance to substance, and that size affects how the substance behaves.

What does the simple model get wrong about the space between particles?

It shows the spheres as touching or evenly spaced, but the amount of space between real particles differs between the states and is not represented properly.

Explain why real particles cannot be solid spheres.

An atom is mostly empty space, with a tiny nucleus and electrons in the space around it, so it is not solid throughout.

OCR GCSE Chemistry A J248

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 Nanoparticles: size and surface area to volume Uses and risks of nanoparticulate materials

Global Challenges

Topic overview Extracting metals by reduction and by electrolysis Biological methods of metal extraction Rate against yield in industry, and reaction conditions The Haber process and fertiliser production Nitrogen, phosphorus and potassium in agriculture Life cycle assessment Recycling, and the decisions behind it Alloys, and the corrosion of metals Comparing glass, ceramics, polymers, composites and metals Functional groups and homologous series Predicting the products of organic reactions Addition polymerisation Condensation polymerisation, and making a polymer DNA and other natural polymers Fractional distillation of crude oil The fractions, and crude oil as a feedstock Dependence on hydrocarbons, and cracking Chemical cells and fuel cells 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 Concentration in mol/dm³, and titration Titration calculations, and the mass of a solute Molar gas volume and the volumes of gases Theoretical mass and percentage yield Atom economy, and choosing a reaction pathway 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 Transition metals Predicting reactivity from the Periodic Table Reactivity of metals with water and acids Tests for oxygen, hydrogen, carbon dioxide and chlorine Tests for aqueous cations and anions Flame tests, and identifying metal ions Identifying a species from test results Instrumental methods of analysis

Particles

Limitations of the particle model

3 things to know
Paper 3

Overview

How the simple model pictures particles as solid spheres, the forces, size differences and spacing it leaves out, why real atoms are not solid, why it cannot explain condensing, and why it is still useful.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How does the simple particle model picture particles, what property is left out, and why does leaving out forces make boiling points hard to explain?

Key term

In the simple particle model, how are the particles pictured?

Key term

State one important property of real particles that is ignored when they are drawn as solid spheres.

Questions from this subtopic

Each one with the model answer underneath.

1
In the simple particle model, how are the particles pictured?
Model answer
As solid, inelastic spheres, rather like tiny bowling balls, with nothing acting between them.
2
State one important property of real particles that is ignored when they are drawn as solid spheres.
Model answer
The forces of attraction that act between the particles are ignored.
3
Explain why leaving out the forces between particles makes the model poor at explaining boiling points.
Model answer
Boiling requires enough energy to overcome the attraction between the particles, so a model with no forces cannot explain why different substances boil at different temperatures.
4
Why is it a limitation that the model draws every particle as a sphere of the same size?
Model answer
Real particles differ in size from substance to substance, and that size affects how the substance behaves.
5
What does the simple model get wrong about the space between particles?
Model answer
It shows the spheres as touching or evenly spaced, but the amount of space between real particles differs between the states and is not represented properly.
6
Explain why real particles cannot be solid spheres.
Model answer
An atom is mostly empty space, with a tiny nucleus and electrons in the space around it, so it is not solid throughout.

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Chemical Reactions

Elements, Compounds and Mixtures

Global Challenges

Monitoring and Controlling Chemical Reactions

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