Scientific models
Scientists use modelAn equation, diagram or analogy that helps explain a scientific idea. 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 ethicalRelating to right and wrong, eg ethical companies are often ones that act in a responsible way. 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 |
| Type of model | Representational model |
|---|---|
| Description | Uses shapes or analogies to describe a system |
| Example | Using a scale model to represent distances and sizes in space |
| Type of model | Descriptive model |
|---|---|
| Description | Uses words or diagrams to describe the features of a system and how they interact |
| Example | A street map is a descriptive model that allows a route from one place to another to be worked out |
| Type of model | Mathematical model |
|---|---|
| Description | Uses patterns of data of past events, known scientific relationships and calculations to make predictions |
| Example | Equations of motion model the movement of bodies |
| Type of model | Computational model |
|---|---|
| Description | A mathematical model that needs a computer to carry out complex calculations |
| Example | Climate change and weather forecasting require computers to analyse the vast amounts of historical data |
| Type of model | Spatial model |
|---|---|
| Description | A model used to show how data appears in three dimensions |
| Example | Molecular 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.
| 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. |
| Year | 1897 |
|---|---|
| Scientist(s) | Thomson |
| New evidence | The discovery of electrons. |
| Changes to the atomic model | 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. |
| Year | 1909 – 1911 |
|---|---|
| Scientist(s) | Rutherford (and Geiger and Marsden) |
| New evidence | Some positively charged particles fired at gold foil bounced back when they were expected to pass straight through. |
| Changes to the atomic model | Atoms have a central positive nucleus. Most of the mass of an atom is found in the nucleus. |
| Year | 1913 |
|---|---|
| Scientist(s) | Bohr |
| New evidence | In-depth work on Rutherford's model showed it had limitations. The electrons should just spiral in towards the positive nucleus. |
| Changes to the atomic model | Electrons move in fixed orbits around the nucleus called electron shells. |
Question
What data caused scientists to change the plum pudding modelThe scientific idea that an atom is a sphere of positive charge, with negatively charged electrons in it. model?
Data collected by Rutherford and his team showed that some positively charged particlesParticles, usually ions or electrons, that carry electrical charges. 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 massThe amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). of the atom is found in a central positive nucleusThe central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei.. This explained why positive particles were repelled and deflected when fired at the gold foil.