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Lecture notes Science (ECDE)
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- Science (ECDE)
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- South African College Schools (SACS High)
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Science made easyBasic atomic theory
Introduction
What is electricity? Why do we have to study electricity or
electronics? Because of the mere fact that electricity has such
a huge impact on our lives, we need to know more about its
uses, its usefulness and its dangers. This study of electricity will
allow us to select and use electrical or electronic products
intelligently, understand how they operate, how they are
designed and manufactured, how they can be made more
efficient, what their limitations are and why, and much more. In
addition, should you find the study of electricity and electronics
so interesting, it can open new avenues of interest in terms of
career and hobby possibilities.
Composition of matter
In order to gain an understanding of what electricity is, it is
useful to have an understanding of matter.
Matter
Matter can be defined as anything that occupies space and has
weight. Matter is anything you can see, feel or use and can
exist in the form of gases, liquids or solids. A good example is
water. Water may be a solid (ice), a liquid (water) and a gas
(vapour). Whether it is ice, liquid or water vapour, its chemical
make-up has not been changes but the state in which it
appears has changed.
Elements
The universe is made of fundamental building blocks called
elements. These are the basic materials that make up all
matter. There are about 100 known elements: silver, Gold,
Copper, Hydrogen, Oxygen, Germanium, Silicon, Helium and
, Uranium are all examples of elements. Everything we see
around us is made from elements. The elements themselves
cannot be produced by chemical combination or separation of
other elements.
Compounds
Combinations of different elements can combine to form a
compound. Water, sugar and rust are examples of compounds.
We can separate water into its original elements, hydrogen and
oxygen, but that is as far as we can go, for hydrogen and
oxygen are both elements.
Molecules
A molecule is the smallest particle that a compound can be
reduced to before it breaks down into its elements. For
example, if we took a grain of sugar and kept breaking it in half
till it got as small as it possibly could and yet still be sugar, we
would have a molecule of sugar. If we then broke it in half gain,
the sugar molecule would change into its elements.
The atom
The atom is the smallest particle that an element can be
reduced to and still keep the properties of that element.
Structure of an Atom
One of the simplest working models of the atom is the Bohr
model, which was developed by Niels Bohr. At the center of the
atom is a nucleus that consists of protons and neutrons.
Revolving around the nucleus are electrons. Electrons have a
negative charge; protons have a positive charge and neutrons
have no charge. Electrons move in orbits (or shells) around the
nucleus much like planets move around the sun. The number of
electrons in any atom equals the number of protons, i.e. all
atoms are electrically neutral. All electrons are alike and all
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