|
|
3.1 | |
Copper Media | |
| 3.1.1 | |
Atoms and electrons |
All matter is composed of atoms. The
Periodic Table of Elements lists all known types of atoms and
their properties. The atom is comprised of:
To help explain the electrical
properties of elements/materials, locate helium (He) on the periodic table.
The Danish physicist, Niels Bohr,
developed a simplified model to illustrate the atom.
One of the laws of nature, called
Coulomb's Electric Force Law, states that opposite charges react to
each other with a force that causes them to be attracted to each
other. Like charges react to each other with a force that causes them
to repel each other. In the case of opposite and like charges, the
force increases as the charges move closer to each other. The force
is inversely
proportional to the square of the separation distance. When particles
get extremely close together, nuclear force overrides the repulsive
electrical force and keeps the nucleus together. That is why
a nucleus does not fly apart.
Examine Bohr's model of the helium atom. If Coulomb's law is true, and if Bohr's model describes helium atoms as stable, then there must be other laws of nature at work. How can they both be true?
Electrons stay in orbit, even though the protons attract the electrons. The electrons have just enough velocity to keep orbiting and not be pulled into the nucleus, just like the moon around the Earth. Protons do not fly apart from each other because of a nuclear force that is associated with neutrons. The nuclear force is an incredibly strong force that acts as a kind of glue to hold the protons together. The protons and neutrons are bound together by a very powerful force. However, the electrons are bound to their orbit around the nucleus by a weaker force. Electrons in certain atoms, such as metals, can be pulled free from the atom and made to flow. This sea of electrons, loosely bound to the atoms, is what makes electricity possible. Electricity is a free flow of electrons. Loosened electrons that stay in one
place, without moving, and with a negative charge, are called static
electricity.
ESD, though usually harmless to people, can create serious problems for sensitive electronic equipment. A static discharge can randomly damage computer chips, data, or both. The logical circuitry of computer chips is extremely sensitive to electrostatic discharge. Use caution when working inside a computer, router, and so on. Atoms, or groups of atoms called molecules, can be referred to as materials. Materials are classified as belonging to one of three groups depending on how easily electricity, or free electrons, flows through them. The basis for all electronic devices is the knowledge of how insulators, conductors and semiconductors control the flow of electrons and work together in various combinations.
|
Helium has
an atomic number of 2, which means that helium has 2 protons and 2
electrons. It has an atomic weight of 4. By subtracting the atomic
number (2) from the atomic weight (4), it is learned that helium also
has 2 neutrons. 
This
illustration shows the model for a helium atom. If the protons and
neutrons of an atom were the size of an adult (#5) soccer ball in the
middle of a soccer field, the only thing smaller than the ball would
be the electrons. The electrons would be the size of cherries and
would be orbiting near the outer-most seats of the stadium. In other
words, the overall volume of this atom, including the electron path,
would be about the size of the stadium. The nucleus of the atom where
the protons and neutrons exist would be the size of the soccer ball. 
If these
static electrons have an opportunity to jump to a conductor, this can
lead to electrostatic discharge (ESD). A discussion on conductors
follows later in this chapter. 
Lab Activity
Web Links