The document provides information about isotopes and how atomic weight is calculated. It explains that isotopes of an element have the same number of protons but different numbers of neutrons. It also states that the atomic weight shown on the periodic table is an average that takes into account the isotope percentages found in nature. An example is provided to show how to calculate the atomic weight of boron using the natural abundances of its two main isotopes.

1. Bring Your
“Matter and
Energy” Book!!
We will do
questions from the
book, so you will
need it!!

2. Isotopes
Foundation Science 4 Class Code SC22102

3. Isotopes
Isotopes of an element have the same number of protons,
but different numbers of neutrons.
So, helium (He) has 2 protons. Isotopes of Helium all have 2
protons and 4 or 6 neutrons.

4. Isotopes

5. Isotopes
with more
neutrons
are heavier

6. How is the Atomic Weight
Calculated?
The isotope percentages of
a naturally occurring
element are averaged
Isotopes are why
the atomic
weight numbers
have decimals
Atomic weight is
simply the mass
of the element in
nature (isotope
% included)

7. If you look in the periodic table you will be able to check that our answer is correct!
Calculate Atomic Weight
The natural abundance for
boron isotopes is: 19.9% 10B
(10.013 amu) and 80.1% 11B
(11.009amu). What is the
atomic weight of boron.
If you look at boron (B) on the
periodic table in your dynamic
earth book, you can check that
your answer is correct! Keep
trying until you get the right
Example from
carbon to help
you…..