Models

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. A model's usefulness is limited by how accurately it represents the real world.

The table shows the different types of model.

Type of modelDescriptionExample
Representational model Uses shapes or analogies to describe a systemUsing a scale model to represent distances and sizes in space
Descriptive modelUses words or diagrams to describe the features of a system and how they interactA street map is a descriptive model that allows a route from one place to another to be worked out
Mathematical model Uses patterns of data of past events, known scientific relationships and calculations to make predictionsEquations of motion model the movement of bodies
Computational modelA mathematical model that needs a computer to carry out complex calculationsClimate change and weather forecasting require computers to analyse the vast amounts of historical data
Spatial modelA model used to show how data appears in three dimensionsMolecular models show the structure of chemicals such as the DNA double helix

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
1897Thomson The 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.
Question

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.

Question

How did Rutherford change the atomic model to provide a scientific explanation that 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.