Scientists use models to explain ideas and to test predictions.

A model:

  • is a simpler representation of something
  • includes the key features of the thing being represented
  • shows how these key features connect with each other
  • is used to explain things, solve problems or to make predictions

Models can help to investigate an idea without ethical or practical difficulties.

However, a model cannot explain everything. Models have limitations.

The table shows the different types of model.

Type of modelDescription
Representational modelUses shapes or analogies to describe a system
Descriptive modelUses words to describe the features of a system and how they interact
Mathematical modelUses patterns of data of past events, known scientific relationships and calculations to make predictions
Computational modelA mathematical model that needs a computer to carry out complex calculations
Spatial modelA computational model used to show how predicted data appears in three dimensions

Particle model

The particle model is an example of a representational model. It can be used to explain and predict the behaviour of substances in the solid, liquid and gas states.

It has limitations. For example, it cannot explain why melting points vary between substances.

Representations of atoms and ions

Representations of atoms and ions, and the use of diagrams to explain bonding, are all examples of models. They help to explain these features, but their limitations mean that they do not explain other aspects of the substances involved. Balanced chemical equations and half equations are models that explain what happens during a chemical reaction.

Modelling climate change

Scientists use computational models to predict the Earth's climate in the future. This is based on historic data and understanding of how climate events are related. It is important that the data used is of high quality. This increases confidence in the prediction.

Industrial modelling

Before any decisions are made about large scale production, chemical reactions used in industry can be modelled in the laboratory or on a computer. This helps to find out about possible problems and avoids the cost of correcting these later. These models can be refined to ensure maximum yield.

The Development of the atomic model

Models change over time. Over the years, scientists developed models to explain the structure of the atom. Scientists used the model to make predictions about their experiments.

Often the data did not agree with their predictions. This meant that the model had to be changed.

The modern atomic model is the result of many scientists building on each other's work.

YearScientist(s)New evidenceChanges to the atomic model
1897ThomsonThe discovery of electrons.Atoms can be broken down into smaller parts. An atom is made of tiny negatively charged electrons dotted about a positively charged sphere like a plum pudding.
1909-1911Rutherford (and Geiger and Marsden)Some positively charged particles fired at gold foil bounced back when they were expected to pass straight through.Atoms have a central positive nucleus. Most of the mass of an atom is found in the nucleus.
1913BohrIn-depth work on Rutherford's model showed it had limitations. The electrons should just spiral in towards the positive nucleus.Electrons move in fixed orbits around the nucleus called electron shells.

What data caused scientists to change the plum pudding model?

Data collected by Rutherford and his team showed that some positively charged particles were repelled and deflected when fired at gold foil. This was not predicted by the plum pudding model.


How did Rutherford change the atomic model to provide a scientific explanation accounted for the new data?

Rutherford proposed that most of the mass of the atom is found in a central positive nucleus. This explained why positive particles were repelled and deflected when fired at the gold foil.