Which particle did Thomson discover, and what did its discovery show about the atom?

He discovered the electron, which showed that atoms contain even smaller, negatively charged particles and so are not indivisible.

Describe the experiment carried out by Geiger and Marsden.

They fired alpha particles at a very thin sheet of gold foil and recorded the directions in which the particles travelled afterwards.

Explain how Rutherford interpreted the results of the alpha scattering experiment.

He concluded that an atom is mostly empty space with its positive charge and nearly all its mass concentrated in a tiny nucleus at the centre.

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

How the atomic model changed, and the structure of the atom

3 things to know
Paper 9 (Chemistry)

Overview

How the model of the atom developed from Dalton's solid sphere through Thomson's electron and plum pudding model, Geiger and Marsden's alpha scattering experiment and Rutherford's nucleus to Bohr's shells and Chadwick's neutron, why models change with new evidence, and the structure of the atom: its charged nucleus, its tiny size, where its mass lies, and why it is neutral and mostly empty space.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How did Dalton describe the atom?

Key term

Describe the plum pudding model of the atom.

Key term

What two results of the alpha scattering experiment were unexpected?

Questions from this subtopic

Each one with the model answer underneath.

1
How did Dalton describe the atom?
Model answer
As a tiny solid sphere that could not be broken down, with all the atoms of a particular element being identical.
2
Which particle did Thomson discover, and what did its discovery show about the atom?
Model answer
He discovered the electron, which showed that atoms contain even smaller, negatively charged particles and so are not indivisible.
3
Describe the plum pudding model of the atom.
Model answer
The atom was pictured as a ball of positive charge with tiny negative electrons scattered through it.
4
Describe the experiment carried out by Geiger and Marsden.
Model answer
They fired alpha particles at a very thin sheet of gold foil and recorded the directions in which the particles travelled afterwards.
5
What two results of the alpha scattering experiment were unexpected?
Model answer
Most of the alpha particles passed straight through the foil, but a very small number were deflected through large angles or bounced straight back.
6
Explain how Rutherford interpreted the results of the alpha scattering experiment.
Model answer
He concluded that an atom is mostly empty space with its positive charge and nearly all its mass concentrated in a tiny nucleus at the centre.

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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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