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.
The table shows the different types of model.
| Type of model | Description |
| Representational model | Uses shapes or analogies to describe a system |
| Descriptive model | Uses words to describe the features of a system and how they interact |
| Mathematical model | Uses patterns of data of past events, known scientific relationships and calculations to make predictions |
| Computational model | A mathematical model that needs a computer to carry out complex calculations |
| Spatial model | A computational model used to show how predicted data appears in three dimensions |
| Type of model | Representational model |
|---|---|
| Description | Uses shapes or analogies to describe a system |
| Type of model | Descriptive model |
|---|---|
| Description | Uses words to describe the features of a system and how they interact |
| Type of model | Mathematical model |
|---|---|
| Description | Uses patterns of data of past events, known scientific relationships and calculations to make predictions |
| Type of model | Computational model |
|---|---|
| Description | A mathematical model that needs a computer to carry out complex calculations |
| Type of model | Spatial model |
|---|---|
| Description | A computational model used to show how predicted data appears in three dimensions |
Particle model
The particle model The scientific theory used to explain the properties of solids, liquids and gases. It involves the arrangement and movement of the particles in a substance. 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 pointThe temperature at which a solid changes into a liquid as it is heated. vary between substances.
Representations of atoms and ions
Representations of atomThe smallest part of an element that can exist. and ionElectrically charged particle, formed when an atom or molecule gains or loses electrons., 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 equationA chemical equation written using the symbols and formulae of the reactants and products, so that the number of units of each element present is the same on both sides of the arrow. and half equationAn equation, involving ions and electrons, that describes the process happening at an electrode. are models that explain what happens during a chemical reaction.
Modelling climate change
Scientists use computational models to predict the Earth's climateAverage weather conditions over longer periods and over large areas. 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 yieldThe mass of product made in a chemical reaction. The percentage yield is a measure of the yield obtained compared to the maximum possible 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.
| 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.?
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 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.