Models of an Atom – SS3 Physics Lesson Note (Second Term)

An atom is a tiny particle that makes up matter, with an estimated diameter of 10^-10 m. Scientists use mathematics and models to understand its structure and behaviour. The main models are Dalton’s, Thomson’s plum pudding, Rutherford’s nuclear model, Bohr’s model and the electron cloud model, each of which has improved our understanding of atoms.

Behavioural objectives

At the end of the lesson, students should be able to:

1. State and discuss what chemical evidence there is for the existence of atoms.
2. Explain what experimental evidence there is for believing that matter is electrical.
3. Explain the Bohr-Rutherford model of an atom.

Instructional resources

A chart showing the diagram of an atom.

What are the models of the atom?

Over the years, scientists have developed many different models of the atom. Each model has helped us to understand the structure and behaviour of atoms better. Atoms are so small that we cannot see them without the help of a powerful microscope. The various models of the atom are as follows:

1. Dalton’s atomic model
2. The plum pudding model, proposed by J. J. Thomson
3. The planetary or nuclear model, proposed by Ernest Rutherford
4. Bohr’s atomic model
5. The electron cloud atomic model

What is Dalton’s atomic model?

Dalton’s atomic model (1803) was the first model of the atom. Dalton proposed that atoms are indivisible and that they are like the building blocks of matter.

What is Thomson’s model?

J. J. Thomson proposed this model in 1904. It is known as the plum pudding model. It depicts the atom as a sphere of positive charge with electrons embedded in it.

What is Rutherford’s model?

In 1911, Ernest Rutherford proposed a new model of the atom, known as the nuclear model. This model depicted the atom as mostly space, with a small, dense nucleus at the centre. The nucleus contains the protons and neutrons, while the electrons orbit the nucleus.

Application

The teacher guides students to mention applications of the photoelectric effect, such as:

1. They are used in line spectra.
2. They are used in the study of the atom.

Evaluation

Mode: Whole class

Teacher’s role: Ask the students to answer the following questions.

1. Explain J. J. Thomson’s atomic model.
2. What was the success of Thomson’s atomic model?

Students’ role: Answer the questions.

Assignment

Study the nucleus for the next class.

Reference material

1. New System Physics for Secondary Schools by Dr. Charles Chew et al.
2. New School Physics by M. W. Anyakoha
3. Internet facility