After
reading this section you will be able to do the following:
Define
and determine the atomic number of an atom.
Define
and determine the mass number of an atom.
What is an
atom's atomic number?
The number of protons
in the nucleus of an atom determines an element's atomic number.
In other words, each element has a unique number that identifies
how many protons are in one atom of that element. For example,
all hydrogen atoms, and only hydrogen atoms, contain one proton
and have an atomic number of 1. All carbon atoms, and only carbon
atoms, contain six protons and have an atomic number of 6. Oxygen
atoms contain 8 protons and have an atomic number of 8. The atomic
number of an element never changes, meaning that the number of
protons in the nucleus of every atom in an element is always the
same.
What is an atom's
mass number?
All atoms have a mass number which
is derived as follows.
Review:
An element's
or isotope's atomic number tells how many protons are
in its atoms.
An element's
or isotope's mass number tells how many protons and neutrons
in its atoms.
