# Atomic structure for OCR GCSE Chemistry 1. Atomic models
2. Subatomic particles

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. Each element has a characteristic number of protons, called the atomic number, which can be found in the periodic table. In atoms the number of electrons is the same as the number of protons. Since they have opposite charges, this ensures that every atom is neutral.

In atoms:
number of protons = atomic number
number of electrons = atomic number
number of neutrons = mass number − atomic number

For charged ions, the number of negatively charged electrons changes. Negative ions will have a higher number of electrons since they have a negative charge that comes from the negative electrons. Thus, positive ions will have the usual number of electrons that belongs to the atoms minus their charge which indicates the number of electrons lost. # 1

Which part of an atom contains positively charged particles?

The nuclear model states that an atom is a nucleus cotaining protons and neutrons surrounded by electrons in energy shells. Since protons are positive, the positive charge in the atom is in the nucleus.

nucleus # 2

Identify the element and ionic charge from the diagram representing an ion.

atomic number = number of protons = 4
Beryllium has an atomic number of 4 and as an atom has 4 electrons.
2 electrons are missing, thus, this is an ion with a charge of 2+.

beryllium, 2+ # 3

How many protons, neutrons and electrons does a F⁻ ion have?

number of protons = atomic number = 9
number of neutrons = atomic mass − atomic number = 19 − 9 = 10
number of electrons in a F atom = atomic number = 9
− charge in the ion means that one electron has been gained.
number of electrons in F⁻ = 9 + 1 = 10

9 protons, 10 neutrons, 10 electrons # 4

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 # 5

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 couldn’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 → plum pudding → particle scattering experiment → nuclear model End of page