1. Essential Question: How do atoms of the same element differ?
Isotopes
Essential Question: How do atoms of the same element differ?

2. What is an Isotope?
Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons.
All elements consist of naturally occurring isotopes and artificially produced isotopes

3. How are isotopes of an element similar? How are they different?
The isotopes of an element have:
Identical Chemical Properties (this is because they have the same numbers of protons and electrons and subatomic particles are responsible for chemical behavior)
Different Physical Properties (different mass and different number of neutrons)

4. How do we represent specific isotopes?
Nuclear symbols are used to represent specific isotopes
To write a nuclear symbol:
1.) the symbol of the element is written first
2.) the mass number is written as a
superscript to the left of the symbol
3.) the atomic number is written as a
subscript to the left. Study the illustration below
Li-7 isotope

5. Learning Check
Given a nuclear symbol, what does the top left number represent?
What does the bottom left number represent?

6. Can we write isotopes in a different way?
You can also use the mass number and the name of the element to designate the atom or isotope
This is called hyphen notation
For example, two isotopes of carbon are carbon-12 and carbon-13
The nuclear symbols for these two isotopes would be: C 12 6 13 6 C

7. Learning Check
What does the number after the hyphen represent?

8. What do the numbers used when writing isotopes represent?
The mass number
total number of protons and neutrons in a specific nucleus of an atom.
The atomic number
always refers to the total number of protons in an atom.

9. How do I figure out the number of neutrons when writing isotopes?
To determine the number of neutrons in a specific isotope
subtract the atomic number from the mass number
See the formula below
Mass Number (neutrons + protons)
Atomic Number (number of protons)
(number of neutrons)

10. Learning Check Boron consists of two isotopes, B-10 and B-11
1.) Determine the number of neutrons in each of the
isotopes
2.) Using the periodic table, write the nuclear symbol
for each isotope given in hyphen notation
a.) B-10: – 5 = 5 neutrons
b.) B-11: – 5 = 6 neutrons

11. What does the atomic weight of an element depend on?
To identify isotopes the mass number is placed after the element’s name
Ex: chlorine-35 potassium-37
The atomic weight of an element depends on the abundance of its isotopes.
If you know the mass of the isotopes and the percent (fractional) abundance of the isotopes, you can calculate the element's atomic weight.

12. How do I calculate the atomic mass of an element based on percent natural abundance and isotopic masses?
Example: Chlorine has 2 naturally occurring isotopes
To calculate the average atomic weight:
add the mass of each isotope multiplied by its percent abundance
This is the solution for chlorine:
( ) * (0.7577) + ( ) * (0.2423) = amu
Mass #
Mass
Percent Abundance 35
75.77 37
24.23

13. Learning Check Nuclear Symbol
Complete based on the following information:
29 protons, mass 65
Barium - 138
17 protons, mass 36
Tin - 120
16 protons, mass 30