Page 4 - Curriculum Visions Dynamic Book

An element is a substance that cannot be broken down into a simpler substance by any known means. Each of the 92 naturally occurring elements is therefore one of the fundamental materials from which everything in the Universe is made. This book is about uranium
and other radioactive elements.
Radioactive elements
In chemical reactions, the atoms that make up the elements do not change. However, in some circumstances the atoms can be made to change (such as when two hydrogen atoms are made to fuse together to produce a helium atom) and some elements, such as uranium, continually change. Elements that continually change are called radioactive elements.
All atomic change is characterised by
a release of energy, which may be in the form of heat alone, heat and light together, or, as in the case of the radioactive elements, heat, light and the release of “radiation”
(rays or particles of matter).
All the elements with an atomic number of 88 and above in the Periodic Table
(see page 46) are radioactive. In addition, some common elements (such as hydrogen, oxygen and carbon) have radioactive forms called isotopes.
The changes in radioactive elements
take place in the core, or nucleus, of the element’s atoms. This is why scientists call them nuclear reactions and why we use such terms as nuclear energy and nuclear bombs.
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