Atoms
Atoms are the basic building blocks of matter. Every thing is made of
atoms, rocks, living things, the Earth, the stars, all that we can see.
What are atoms made of?
Subatomic
particles
The modern quantum atomic theory of the atom states that all atoms have
three fundamental parts (or subatomic particles): protons, neutrons and
electrons. All three can exist by themselves, but it is when they combine
to form atoms that they become truly spectacular in their behavior.
The nucleus
The protons and neutrons are found tightly bound into a very small, positively
charged, central core called the nucleus. In the average size atom, the
nucleus takes up 100 000th of the diameter of the atom. If the nucleus
of an atom was the size of a marble, then the atom it belonged to would
be about the size of the a football ground. The nucleus is so dense that
if the marble in the middle of the ground was made of only protons and
neutrons it would weigh about 1 000 tonnes.
This extremely small, very dense centre of the atom has nearly all of
the atom's mass and is virtually indestructible in everyday chemical and
physical reactions. It is only in the stars, nuclear reactors, atomic
bombs and during radioactive decay that nuclei can be broken and reformed.
The electrons
The nucleus is surrounded by a "cloud" of very fast moving electrons.
In contrast to the nucleus, this vast empty space has virtually no matter
in it and hence no mass. The light weight electrons can move very fast,
some thousands of kilometres per hour, and act a bit like the blades of
a fan. When the fan is stopped, you can see the spaces between the blades
but, when it is full on, the blades and space blur together and the blades
effectively occupy all the available space.
The electrons are arranged in energy levels and orbitals, or regions
in space where electrons can be found. Scientists describe the arrangement
of electrons using mathematics and "quantum numbers" which uniquely describe
the shape of each orbital and the properties of each electron, the modern
quantum theory goes on to describe a strange subatomic world of wave/particles
and electromagnetic energy.
The atom
There are over 100 known types of atoms in our Universe, all made up of
the three subatomic particles. Each type of atom is identified primarily
by the number of protons it has in its nucleus; for example, the hydrogen
atom has 1 proton, while the uranium atom has 92 protons. The number of
protons an atom has is specified by its "Atomic Number", and it is by
using atomic numbers that scientists can arrange the atoms into some order.
Each atom will also have just enough neutrons to hold all the protons
together in the nucleus. The presence of the neutrons allows two fundamental
forces, the weak and strong nuclear forces, to come into play and form
the tightly bound atomic nucleus.
The atom is made complete by adding the same number of electrons as it
has protons. This makes the whole atom electrically neutral. The electrons
are much more weakly bound to the atom and can move from one atom to another
or even be "rubbed off" an atom. Static electricity is created by electrons
rubbing off atoms and moving to other atoms. It is these electrons which
form the basis for chemical change and the diversity of materials and
substances we have in our modern world.
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