ATOMIC STRUCTURE
The universe, as we know it today, is divided into two parts: matter and energy.
Matter, which is our main concern at this time, is anything that occupies space
and has weight. Rocks, water, air, automobiles, clothing, and even our own
bodies are good examples of matter. From this, we can conclude that matter may
be found in any one of three states: SOLIDS, LIQUIDS, and GASES. All matter is
composed of either an element or combination of elements. As you know, an
element is a substance that cannot be reduced to a simpler form by chemical
means. Examples of elements with which you are in contact everyday are iron,
gold, silver, copper, and oxygen. At present, there are over 100 known elements
of which all matter is composed.
As we work our way down the size scale, we come to the atom, the smallest
particle into which an element can be broken down and still retain all its
original properties. The atoms of one element, however, differ from the atoms of
all other elements. Since there are over 100 known elements, there must be over
100 different atoms, or a different atom for each element.
Now let us consider more than one element at a time. This brings us to the term
"compound." A compound is a chemical combination of two or more elements. Water,
table salt, ethyl alcohol, and ammonia are all examples of compounds. The
smallest part of a compound, which has all the characteristics of the compound,
is the molecule. Each molecule contains some of the atoms of each of the
elements forming the compound.
Consider sugar, for example. Sugar in general terms is matter, since it occupies
space and has weight. It is also a compound because it consists of two or more
elements. Take a lump of sugar and crush it into small particles; each of the
particles still retains its original identifying properties of sugar. The only
thing that changed was the physical size of the sugar. If we continue this
subdividing process by grinding the sugar into a fine power, the results are the
same. Even dissolving sugar in water does not change its identifying properties,
in spite of the fact that the particles of sugar are now too small to be seen
even with a microscope. Eventually, we end up with a quantity of sugar that
cannot be further divided without its ceasing to be sugar. This quantity is
known as a molecule of sugar. If the molecule is further divided, it is found to
consist of three simpler kinds of matter: carbon, hydrogen, and oxygen. These
simpler forms are called elements. Therefore, since elements consist of atoms,
then a molecule of sugar is made up of atoms of carbon, hydrogen, and oxygen.
As we investigate the atom, we find that it is basically composed of electrons,
protons, and neutrons. Furthermore, the electrons, protons, and neutrons of one
element are identical to those of any other element. There are different kinds
of elements because the number and the arrangement of electrons and protons are
different for each element.
The electron carries a small negative charge of electricity. The proton carries
a positive charge of electricity equal and opposite to the charge of the
electron. Scientists have measured the mass and size of the electron and proton,
and they know how much charge each possesses. Both the electron and proton have
the same quantity of charge, although the mass of the proton is approximately
1,827 times that of the electron. In some atoms there exists a neutral particle
called a neutron. The neutron has a mass approximately equal to that of a
proton, but it has no electrical charge.
According to theory, the electrons, protons, and neutrons of the atoms are
thought to be arranged in a manner similar to a miniature solar system. Notice
the helium atom in figure 1-2. Two protons and two neutrons form the heavy
nucleus with a positive charge around which two very light electrons revolve.
The path each electron takes around the nucleus is called an orbit. The
electrons are continuously being acted upon in their orbits by the force of
attraction of the nucleus. To maintain an orbit around the nucleus, the
electrons travel at a speed that produces a counterforce equal to the attraction
force of the nucleus. Just as energy is required to move a space vehicle away
from the earth, energy is also required to move an electron away from the
nucleus. Like a space vehicle, the electron is said to be at a higher energy
level when it travels a larger orbit. Scientific experiments have shown that the
electron requires a certain amount of energy to stay in orbit. This quantity is
called the electron's energy level. By virtue of just its motion alone, the
electron contains kinetic energy. Because of its position, it also contains
potential energy. The total energy contained by an electron (kinetic energy plus
potential energy) is the main factor that determines the radius of the
electron's orbit. For an electron to remain in this orbit, it must neither gain
nor lose energy.
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