Scientists use models to explain ideas and to test 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 model||Description||Example|
|Representational model||Uses shapes or analogies to describe a system||Using a scale model to represent distances and sizes in space|
|Descriptive model||Uses words or diagrams to describe the features of a system and how they interact||A 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 predictions||Equations of motion model the movement of bodies|
|Computational model||A mathematical model that needs a computer to carry out complex calculations||Climate change and weather forecasting require computers to analyse the vast amounts of historical data|
|Spatial model||A model used to show how data appears in three dimensions||Molecular models show the structure of chemicals such as the DNA double helix|
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.
|Year||Scientist(s)||New evidence||Changes to the atomic model|
|1897||Thomson||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 – 1911||Rutherford (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.|
|1913||Bohr||In-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 that accounted for the new data?