Chemistry_Grade_10-12 (1).pdf

Gets bigger in elements with a higher number of

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gets bigger (in elements with a higher number of nucleons), the electromagnetic force becomes greater than the strong nuclear force. In these nuclei, it becomes possible for particles and energy to be ejected from the nucleus. These nuclei are called unstable . The particles and energy that a nucleus releases are referred to as radiation , and the atom is said to be radioactive . We are going to look at these concepts in more detail in the next few sections. 7.2 The Discovery of Radiation Radioactivity was first discovered in 1896 by a French scientist called Henri Becquerel while he was working on phosphorescent materials. He happened to place some uranium crystals on black paper that he had used to cover a piece of film. When he looked more carefully, he noticed that the film had lots of patches on it, and that this did not happen when other elements were placed on the paper. He eventually concluded that some rays must be coming out of the uranium crystals to produce this effect. His observations were taken further by the Polish scientist Marie Curie and her husband Pierre, who increased our knowledge of radioactive elements. In 1903, Henri, Marie and Pierre were 107
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7.3 CHAPTER 7. ATOMIC NUCLEI - GRADE 11 awarded the Nobel Prize in Physics for their work on radioactive elements. This award made Marie the first woman ever to receive a Nobel Prize. Marie Curie and her husband went on to discover two new elements, which they named polonium (Po) after Marie’s home country, and radium (Ra) after its highly radioactive characteristics. For these dicoveries, Marie was awarded a Nobel Prize in Chemistry in 1911, making her one of very few people to receive two Nobel Prizes. Interesting Fact erest Fact Marie Curie died in 1934 from aplastic anemia, which was almost certainly partly due to her massive exposure to radiation during her lifetime. Most of her work was carried out in a shed without safety measures, and she was known to carry test tubes full of radioactive isotopes in her pockets and to store them in her desk drawers. By the end of her life, not only was she very ill, but her hands had become badly deformed due to their constant exposure to radiation. Un- fortunately it was only later in her life that the full dangers of radiation were realised. 7.3 Radioactivity and Types of Radiation In section 7.1, we discussed that when a nucleus is unstable it can emit particles and energy. This is called radioactive decay . Definition: Radioactive decay Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting particles or electromagnetic waves. Radiation is the name for the emitted particles or electromagnetic waves. When a nucleus undergoes radioactive decay, it emits radiation and the nucleus is called radioac- tive. We are exposed to small amounts of radiation all the time. Even the rocks around us emit radiation! However some elements are far more radioactive than others. Isotopes tend to be less stable because they contain a larger number of nucleons than ’non-isotopes’ of the same element. These radioactive isotopes are called
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