CHAPTER 19, SECTION 2
STUDENT NOTES
Atomic Mass
• The
contains most of the
protons and neutrons are far more
• The
of a
of a
— approximately
• The mass of each is approximately
the electron.
of the atom because
than electrons.
is about the
as that
times greater than the mass of
PROTONS IDENTIFY THE ELEMENT
• The number of
tells you what type of atom you have
and vice versa. For example, every
atom has
protons. Also, all atoms with six protons are carbon atoms.
• The number of
_______________
in an atom is equal to a number called the
.
Using the information from the picture to the left, fill in the
following blanks regarding the element:
Name of Element:
Atomic Mass:
Atomic Number:
Chemical Symbol:
1
Mass Number
• The
number of
nucleus of an atom.
of an atom is the
and the number of
of the
in the
• If you know the mass number and the atomic number of an atom, you can
calculate the number of
.
• number of neutrons =
number –
Isotopes
• Not all the atoms of an element have the same number of
number
.
• Atoms of the same element that have different numbers of neutrons are called
________________________.
• Models of two isotopes of
neutrons in the isotopes are
also different.
are shown. Because the numbers of
, the
numbers are
• You use the name of the
followed by the mass number of the
_______________________ to identify each isotope: boron-10 and boron-11.
TIME TO THINK!!!!
If an atom of Carbon has 6 protons and 6 neutrons and is written as
Carbon-12, How many protons and neutrons does Carbon-14 have?
• Protons in carbon 14 • Neutrons in carbon 14 -
2
• The
the
isotopes.
-average mass of the
• For example,
out of
boron-11, and one out of five is boron-10.
of an element is
of its
atoms of boron are
• To find the weighted-average or the
of boron, you would solve the following equation:
3