Page 24 - Teach Yourself Electricity and Electronics

4 Basic physical concepts

Each element has its own unique type of particle, known as its atom. Atoms of differ-
ent elements are always different.
The slightest change in an atom can make a tremendous difference in its behavior.
You can live by breathing pure oxygen, but you can’t live off of pure nitrogen. Oxygen
will cause metal to corrode, but nitrogen will not. Wood will burn furiously in an atmos-
phere of pure oxygen, but will not even ignite in pure nitrogen. Yet both are gases at
room temperature and pressure; both are colorless, both are odorless, and both are just
about of equal weight. These substances are so different because oxygen has eight pro-
tons, while nitrogen has only seven.
There are many other examples in nature where a tiny change in atomic structure
makes a major difference in the way a substance behaves.

Protons, neutrons, and the
atomic number

The part of an atom that gives an element its identity is the nucleus. It is made up of
two kinds of particles, the proton and the neutron. These are extremely dense. A tea-
spoonful of either of these particles, packed tightly together, would weigh tons. Protons
and neutrons have just about the same mass, but the proton has an electric charge
while the neutron does not.
The simplest element, hydrogen, has a nucleus made up of only one proton; there
are usually no neutrons. This is the most common element in the universe. Sometimes
a nucleus of hydrogen has a neutron or two along with the proton, but this does not
occur very often. These “mutant” forms of hydrogen do, nonetheless, play significant
roles in atomic physics.
The second most abundant element is helium. Usually, this atom has a nucleus with
two protons and two neutrons. Hydrogen is changed into helium inside the sun, and
in the process, energy is given off. This makes the sun shine. The process, called fusion,
is also responsible for the terrific explosive force of a hydrogen bomb.
Every proton in the universe is just like every other. Neutrons are all alike, too. The
number of protons in an element’s nucleus, the atomic number, gives that element its
identity. The element with three protons is lithium, a light metal that reacts easily with
gases such as oxygen or chlorine. The element with four protons is beryllium, also a
metal. In general, as the number of protons in an element’s nucleus increases, the num-
ber of neutrons also increases. Elements with high atomic numbers, like lead, are there-
fore much denser than elements with low atomic numbers, like carbon. Perhaps you’ve
compared a lead sinker with a piece of coal of similar size, and noticed this difference.

Isotopes and atomic weights

For a given element, such as oxygen, the number of neutrons can vary. But no matter
what the number of neutrons, the element keeps its identity, based on the atomic num-
ber. Differing numbers of neutrons result in various isotopes for a given element.
Each element has one particular isotope that is most often found in nature. But all
elements have numerous isotopes. Changing the number of neutrons in an element’s