4.2 Models of the atom (ESAAN)

It is crucial to realise that a most what we know about the structure of atoms has actually been occurred over a long period of time. This is often how scientific knowledge develops, v one person building on the principles of who else. We are going come look at how our modern understanding that the atom has developed over time.

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The idea of atom was created by two Greek philosophers, Democritus and Leucippus in the 5th century BC. The Greek indigenous ατoμoν (atom) means indivisible due to the fact that they believed that atoms can not be damaged into smaller sized pieces.

Nowadays, we know that atoms are consisted of of a positively charged nucleus in the centre surrounded by negatively charged electrons. However, in the past, prior to the framework of the atom was properly understood, researchers came up with lots of different models or pictures to explain what atom look like.


A model is a depiction of a device in the real world. Models aid us to know systems and their properties.

For example, one atomic model to represent what the structure of one atom could watch like, based upon what us know about how atom behave. It is not necessarily a true photo of the specific structure of one atom.

Models are frequently simplified. The small toy cars that you may have actually played through as a child are models. They provide you a good idea the what a real auto looks like, yet they are much smaller and much simpler. A design cannot always be absolutely accurate and it is necessary that us realise this, so the we do not build up an untrue idea about something.

Dalton"s version of the atom (ESAAO)

John Dalton proposed that all matter is written of very little things i m sorry he called atoms. This was no a totally new principle as the ancient Greeks (notably Democritus) had proposed the all matter is created of small, indivisible (cannot be divided) objects. Once Dalton suggest his design electrons and also the nucleus to be unknown.


Figure 4.2: The atom according to Dalton.

Thomson"s model of the atom (ESAAP)

After the electron was uncovered by J.J. Thomson in 1897, civilization realised that atoms were consisted of of also smaller particles than they had actually previously thought. However, the atom nucleus had not been uncovered yet and also so the “plum pudding model” was placed forward in 1904. In this model, the atom is comprised of negative electrons that float in a “soup” of positive charge, much like plums in a pudding or raisins in a fruit cake (Figure 4.3). In 1906, Thomson to be awarded the Nobel Prize because that his job-related in this field. However, also with the Plum Pudding Model, there was still no expertise of how these electrons in the atom were arranged.


Figure 4.3: The atom follow to the Plum Pudding model.

The exploration of radiation to be the following step along the path to building an exact picture of atomic structure. In the early twentieth century, Marie and Pierre Curie, found that some facets (the radioactive elements) emit particles, which are able to pass through issue in a similar method to X–rays (read an ext about this in class 11). It to be Ernest Rutherford who, in 1911, offered this exploration to revise the design of the atom.

Two various other models proposed for the atom were the cubic model and the Saturnian model. In the cubic model, the electrons were imagined come lie in ~ the corners that a cube. In the Saturnian model, the electrons were imagined to orbit a really big, hefty nucleus.

Rutherford"s version of the atom (ESAAQ)

Rutherford carried out some experiments which led to a change in ideas about the atom. His new model described the atom as a tiny, dense, positively charged core dubbed a nucleus surrounded by lighter, negatively charged electrons. Another way of thinking about this design was that the atom was seen to be favor a mini solar mechanism where the electrons orbit the nucleus choose planets orbiting roughly the sun. A simplified picture of this is shown alongside. This model is sometimes recognized as the planetary model of the atom.


Figure 4.4: Rutherford"s version of the atom.

Bohr"s design of the atom (ESAAR)

There were, however, some difficulties with Rutherford"s model: for instance it could not describe the an extremely interesting monitoring that atoms only emit irradiate at particular wavelengths or frequencies. Niels Bohr fixed this trouble by proposing that the electrons could only orbit the nucleus in certain special orbits at various energy levels approximately the nucleus.

Figure 4.5: Bohr"s model of the atom.

James Chadwick (ESAAS)

Rutherford suspect (in 1920) that another kind the particle must be current in the nucleus together with the proton. He predicted this due to the fact that if over there were just positively charged protons in the nucleus, climate it have to break right into bits because of the repulsive forces between the like-charged protons! to make sure that the atom continues to be electrically neutral, this fragment would have to be neutral itself. In 1932 James Chadwick found the neutron and also measured that mass.

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Other models that the atom (ESAAT)

Although the most commonly used version of the atom is the Bohr model, researchers are still developing brand-new and boosted theories on what the atom look at like. One of the most vital contributions come atomic theory (the field of scientific research that looks at atoms) was the advancement of quantum theory. Schrodinger, Heisenberg, Born and also many others have had a function in emerging quantum theory.