<p>Sir Joseph John Thomson OM PRS was an English physicist and Nobel laureate in physics, credited with the discovery and identification of the electron; and with the discovery of the first subatomic particle. </p>
<div class="wp-caption alignnone" id="attachment_104461" style="width: 800px"><a href="https://data.ulearngo.com/assets/69a659ec-d510-4d96-bd9f-dbff174aacb1"><img alt="jj-thomson" class="size-full wp-image-104461" height="1250" src="https://data.ulearngo.com/assets/69a659ec-d510-4d96-bd9f-dbff174aacb1" width="800"/></a><p class="wp-caption-text">English physicist J J Thomson. Image credit: public domain</p></div>
<h2>Thomson's Model of the Atom</h2>
<p>After the electron was discovered by J.J. Thomson in 1897, people realised that atoms were made up of even smaller particles than they had previously thought. However, the atomic nucleus had not been discovered yet and so the “plum pudding model” was put forward in 1904. In this model, the atom is made up of negative <a data-lesson="orbital-shapes-and-valence-electrons" data-subject="chemistry" data-tutorial="chemistry-essential-ideas" href="https://app.ulearngo.com/chemistry/chemistry-essential-ideas/orbital-shapes-and-valence-electrons">electrons</a> that float in a “soup” of positive charge, much like plums in a pudding or raisins in a fruit cake (see the figure below). In 1906, Thomson was awarded the Nobel Prize for his work in this field. However, even with the Plum Pudding Model, there was still no understanding of how these electrons in the atom were arranged.</p>
<div class="wp-caption alignnone" style="width: 512px"><img alt="90cffe92260bc3815a6825cbb0d87b39.png" height="311" src="https://data.ulearngo.com/assets/7292a32a-9af0-428f-bea2-5d7b751f0061" width="512"/><p class="wp-caption-text">The atom according to the Plum Pudding model.</p></div>
<p>The discovery of <strong>radiation</strong> was the next step along the path to <a data-lesson="atoms-and-compounds" data-subject="chemistry" data-tutorial="chemistry-essential-ideas" href="https://app.ulearngo.com/chemistry/chemistry-essential-ideas/atoms-and-compounds">building</a> an accurate picture of atomic structure. In the early twentieth century, Marie and Pierre Curie, discovered that some elements (the <em>radioactive</em> elements) emit particles, which are able to pass through matter in a similar way to X–rays (read more about this in Grade 11). It was Ernest Rutherford who, in 1911, used this discovery to revise the model of the atom.</p>
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<h3>Did You Know?</h3>
<p>Two other models proposed for the atom were the cubic model and the Saturnian model. In the cubic model, the electrons were imagined to lie at the corners of a cube. In the Saturnian model, the electrons were imagined to <a data-lesson="energy-electron-bohr-orbit" data-subject="chemistry" data-tutorial="electronic-structure-of-atoms" href="https://app.ulearngo.com/chemistry/electronic-structure-of-atoms/energy-electron-bohr-orbit">orbit</a> a very big, heavy nucleus.</p>
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Thomson's Model of the Atom

Chemistry generally explores the substances of which matter is composed, the investigation of their properties and reactions, and the use of such reactions to form new substances. 

Chemistry

Explore the essential ideas in chemistry, including the scientific method, laboratory skills and safety, states of matter, measurement uncertainty, models of the atom, electronic configurations, and more.


Thomson's Model of the Atom

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