1. Isotopes

2. Atoms of the same element have the same atomic number
Elements have Isotopes
Isotopes are atoms that have the same number of protons, but different numbers of neutrons.
They can be a radioactive form of an element.
Atoms of the same element all have the same number of protons.
Isotopes of the element have different numbers of neutrons.

3. How to name isotopes?
How to write the isotope symbol?
To name isotopes use the name of the element followed by the isotope’s mass number.
Carbon Protons =
Neutrons =
Electrons =
Carbon Protons =

4. Writing isotopes in the language of chemistry
Example of Isotopes of chlorine atom
Isotopes of chlorine
Mass number Cl Mass number 37Cl
Atomic number Atomic Number 17
chlorine chlorine 37
Protons = Protons =
Neutrons = Neutrons =
Electrons = Electrons =
To name isotopes, use the name of the element followed by the isotope’s mass number

5. Learning Check 16 14 14 An atom has 14 protons and 14 neutrons.
1. Its atomic number is
a) b) 0 c) 28
2. Its mass number is
3. The element is
a) Si b) Ca c) Se
4. Another isotope of this element is
a) 28X b) 34X c) 29X

6. Na 22.99 Atomic Mass What is the atomic mass?
Listed on the periodic table
Gives the mass of “average” atom of each element compared to 12C
Average atom based on all the isotopes and their % abundance.
Atomic mass is not a whole number

7. Masses of Atoms Why is the atomic mass not a whole number?
A scale was designed for atoms to give their small atomic masses in atomic mass units (amu)
An atom of 12C was assigned an exact mass of amu
The atomic mass is the average mass of all the isotopes of the element and their percent abundance.

8. Calculating Atomic Mass Need the Percent(%) abundance of isotopes
Also, need the Mass of each isotope of that element
Atomic mass=
mass isotope1(%) + mass isotope2(%) + …

9. Learning Check 7
Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is:
60.2% of gallium 69 atoms
39.8% of gallium 71 atoms
What is the atomic mass of gallium?

10. Solution Atomic mass Ga = 69.8 amu 69 amu x 60.2 = 41.5 amu 100
Ga 69 (%/100) 69Ga
69 amu x = amu
100
Ga 71 (%/100) 71Ga
71 amu x = amu
Atomic mass Ga = amu