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Development of the atom for OCR A-level Chemistry

Development of the atom

This page covers the following topics:

1. The nuclear model

Ernest Rutherford used the results from the particle scattering experiment to propose the nuclear model describing a central positively charged nucleus with orbiting electrons. Niels Bohr described that electrons were occupying energy shells in this way surrounding the nucleus. In 1932 James Chadwick discovered the neutron which suggested that the nucleus consists of protons and neutrons. These discoveries led to the theory of the nuclear model, which is the model of the atom we know today, nucleus containing protons and neutrons surrounded by electrons in energy shells.

The nuclear model

1

Draw a diagram representing the nuclear model including subatomic particles.

In the nuclear model the nucleus containing protons and neutrons is surrounded by electrons in energy shells.

image

Draw a diagram representing the nuclear model including subatomic particles.

2

Where are the electrons in the atom?

Niels Bohr described that electrons were occupying energy shells in this way surrounding the nucleus.

shells around the nucleus

Where are the electrons in the atom?

3

Which scientist provided evidence to support the nuclear model, specifically the composition of the nucleus?

In 1932 James Chadwick discovered the neutron which suggested that the nucleus consists of protons and neutrons.

James Chadwick

Which scientist provided evidence to support the nuclear model, specifically the composition of the nucleus?

4

Describe how and why the atomic model has changed over time.

Dalton first suggested the atom as the tiny particle making up an atom but suggested it couldnโ€™t be divided any further. Thomson discovered the atom and theorised the plum pudding model where atoms are spheres of positive charge with negative charged electrons inside. Rutherford used the results from the particle scattering experiment to propose the nuclear model describing a central positively charged nucleus with orbiting electrons. Bohr described how electrons were occupying energy shells.

tiny sphere โ†’ plum pudding โ†’ particle scattering experiment โ†’ nuclear model

Describe how and why the atomic model has changed over time.

5

Where is the majority of mass in an atom according to the nuclear model?

Mass in an atom is centralised in the nucleus.

nucleus

Where is the majority of mass in an atom according to the nuclear model?

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