When you have finished this page,
try the Atom Quiz.
An atom is the smallest particle
of an element that still is that element.
The atom is made up of several parts.
It has a center part called the nucleus. The nucleus is made up of a positively
charged particle called a proton and a particle that does not have a charge
called a neutron. The nucleus is surrounded by negatively charged particles
called electrons that move in orbits around the nucleus. Most of the mass of
the atom is contained in the nucleus and the mass of the proton and neutron
are about the same. However, the nucleus is a small portion of the total amount
of space the atom takes up. Different types of atoms can be identified by the
numbers of protons, neutrons and electrons they contain and their atomic mass.
Atoms that have the same number
of protons but different numbers of neutrons are called isotopes.
The negatively charged electrons
are very light in mass. An atom is described as neutral if it has an equal number
of protons and electrons or if the number of electrons is the same as the atomic
number of the atom. The electrons that are outermost can combine with other
atoms by giving up or taking on electrons. This can cause atoms to have an electrical
charge and these kinds of atoms are called ions. Atoms can also share electrons
and this is called a chemical bond.
The atomic number of an atom is
the number of protons it has. The atomic weight or mass of the atom is the total
number of protons and neutrons in the atom's nucleus.
