Page 7 - Curriculum Visions Dynamic Book

What makes an element radioactive?
Inside an atom there are three kinds of particle: protons, neutrons and electrons. The nucleus, the tiny core of the atom, contains protons (positively charged particles) and neutrons (so called because they are neutral and have no charge). The region beyond the nucleus contains (negatively charged) electrons that balance out the charge of the protons. The electrons are usually thought of as orbiting the tiny nucleus, like planets orbiting the Sun.
As you would expect, properties of an atom give rise to some of the most important properties of an element. For example, the atomic number of an element is equal to the total number of protons in an atom (the atomic
number of each element is given on pages 46–47). The total number of protons and neutrons gives the atomic weight (mass). There are roughly as many
protons as neutrons, which is why the atomic weight is about (but not exactly) twice the
atomic number.
In some cases several versions of the same
element occur, identical in all their chemical properties and varying only in the number
of neutrons they contain. Each of these variations is called an isotope (meaning
“the same but different”).
Because like charges repel each other,
there is always a force trying to push the protons apart. Provided there are not too
many protons in the nucleus, other forces can hold the protons together. But if the
ratio of protons to neutrons is not within
certain limits, protons may not be held firmly together, and they form an unstable
nucleus. This is what makes isotopes of some elements radioactive.
For example, carbon, the element found in all living things has the chemical symbol C.
The normal form (isotope) has an atomic weight of 12 and is written 12C or carbon-12,
but the radioactive version (the radioactive isotope) has two extra neutrons, so its symbol is
14C (carbon-14). As we shall see, the radioactive form behaves chemically just like the non-
radioactive form, although one will never change into the other.
atom: the smallest particle of an element.
electron: a tiny, negatively charged particle that is part of
an atom. The flow of electrons through a solid material such as a wire produces an electric current.
isotope: atoms that have the same number of protons in their nucleus, but which have different masses; for example, carbon-12 and carbon-14.
neutron: a particle inside the nucleus of an atom that is neutral and has
no charge.
proton: a positively charged particle in the nucleus of an
atom that balances out the charge of the surrounding electrons.
Also...
The origin of the elements
Why do we have so many different elements and where did they form? This is a question that a nuclear scientist is best able to answer, because the answer lies in the core, or nucleus, of atoms.
At the beginning of time
(the instant of the creation of the known Universe, called the Big Bang) the only element in existence was hydrogen. All the other elements are, in some way or another, “daughters” of hydrogen. So, for example, hydrogen atoms are forced together (fused) to make helium and so on down a long line. In this line carbon, for example, is transformed into oxygen. Together the elements created by fusion make the stuff of life.
Nuclear reactions are the most fundamental of all reactions, creating the elements themselves. They are going on today, just as they have
been happening since the Big Bang. Most nuclear activity occurs in the stars, although a small amount is happening in the rocks of the Earth. But even nuclear reactions on a small scale are noticeable because of the outpouring of energy – radiation – that accompanies any nuclear change.
7
7