ATOMS AND ELEMENTS
An element is any substance that cannot be broken down into a simpler
substance by a chemical reaction.
Now, what exactly is an atom? Suppose you have a spoonful of some element—
carbon, for instance. The smallest, tiniest, teeniest “piece” of carbon in the
spoonful is one atom of carbon. Technically, an atom is the smallest particle of
an element that still retains the chemical properties of that element.
Small Particle,
Big History
The concept of an atom
has been kicking around
since ancient Greece, but
it wasn’t until the early
1800s that the English
scientist John Dalton
supported these theories
with measurements. His
proposal was that all
elements were made up of
atoms and, furthermore,
that all atoms of a given
element were identical
to one another. He also
stated that atoms of different
elements therefore
had different masses and
that a chemical reaction
would involve the rearrangement
of atoms.How an Atom Is Made: Protons, Neutrons, and Electrons
At the center of every atom is a nucleus. What makes up the nucleus of an atom?
Two things: protons and neutrons. Protons have a charge of +1, and neutrons
have no charge at all—they are neutral. Because protons and neutrons comprise
the nucleus of an atom, they are sometimes referred to as nucleons. What’s
outside the nucleus? Electrons; electrons have a charge of −1.
In an electrically neutral atom, the number of electrons is equal to the number of
protons; the charges inside and outside the nucleus are balanced.