|What is an atom?
|Question Date: 2003-04-17|
All of matter is made up of smaller particles. At
the smallest level scientists understand, there
are tiny particles called "subatomic"
particles. They are the smallest particles
because we don't
know how to break them up into something smaller.
And there are a lot of them. One of these
particles, called an "electron", is what
electricity is made from. Some of the other
particles combine to form objects called
and "neutrons". These protons and neutrons
combine with electrons to make atoms.
kinds of atoms have different numbers of protons,
neutrons, and electrons. For example, oxygen,
which we all need to breathe, is made from 8
protons, 8 electrons, and 8 neutrons.
also combine together to make things called
molecules - water is made from two hydrogen
and one oxygen atom. And molecules combine
together to make everything - you, me, this
computer, your school, your house, the sun -
everything. If you understand about atoms,
you understand the most important thing to know
Actually (like many simple questions) your
question is difficult to answer. Many years (about
2000) ago, the Greek philosopher, Democritus
realized that if you keep breaking down something
(say a piece of metal such as gold) into smaller
and smaller parts you get smaller and smaller
pieces of gold. But if you go on in this manner,
you will finally reach a stage when the pieces
that you have are no longer gold. He used this
idea to say that all materials are made up of
small "things" called atoms, and anything smaller
than an atom will not have any resemblance to the
In more modern terms, we know
that there are a certain number(about a 100) of
chemical elements (can you name some ?) and all of
these are made up of unique atoms --- gold atoms
are different from carbon atoms. But if you break
up a gold atom,what you have is no longer
Atoms are very small. 1 g of gold has
approximately 3 000 000 000 000 000 000 000 atoms.
Scientists and philosophers wondered for many
years about the smallest components of all
material things. The Greeks thought that all
matter was made up of small particles of four
elements: Earth, Air, Fire and Water. By the end
of the 18th century, experiments with simple
chemicals led some scientists (Priestly,
Lavoisier, Dalton) to postulate that all matter
was made up of a fairly small set of chemical
'atoms' which combined to make all kinds of
matter, but could not be broken down.
are about 100 known elements, each having a
particular atom. Everything is made of such atoms,
including the air, water, fire and earth of the
ancients. The only things you are likely to have
seen which are not composed of atoms is light and
Most simply, atoms can be
though of as having a core (nucleus) which is
massive and positively changed, and a cloud of
much lighter electrons which are negative and
balance the positive charge. Although atoms are
not broken down in known chemical reactions, they
can be broken or fused at much higher energies
such as in the core of the sun or a nuclear
reactor. So, although they are not the
simplest nor the smallest particles of matter,
atoms are the smallest particles for which
chemical reactions such as fire have meaning.
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