1. The Parts of the Atom
e- p n
1- 1+ 0
Electron cloud
around the nucleus nucleus
nucleus
1/1,840 1 1

2. Which two particles are responsible for the
mass of an atom?
Protons and Neutrons
Which two particles are responsible for the
charge of an atom?
Protons and Electrons

4. 26
Atomic Number
Atomic Number
Fe
Iron
55.845 Atomic Mass
Atomic Mass
Atomic Number = 26
26
Atomic Mass = 55.845
55.845
Mass # = 56
56
# of Protons = 26
26
# of Neutrons = 30
30
# of Electrons = 26
26

5. Notes and Guided Practice

6. Different Elements—Different
Numbers of Protons
the number of protons
The type of
the number of electrons
element

7. What are the atomic numbers of carbon, nitrogen and oxygen?
Carbon = 6, Nitrogen = 7, Oxygen = 8
Explain the difference between an oxygen atom and a carbon atom.
Oxygen has 8 protons. Carbon has 6 protons.

8. Neutrons and Isotopes
• Isotopes are atoms of the same element
that have different numbers of neutrons.
Most elements have several isotopes.
Same Different

9. How do the carbon isotopes differ?
Carbon isotopes have different numbers of neutrons

10. Atomic Number vs. Mass Number
The number of The number of
protons protons and neutrons
Hint :
# of neutrons = mass # - protons

11. Average Atomic Mass
The average atomic
mass of an element is
the average mass of the
element’s isotopes,
weighted according to
the abundance of each
isotope.

12. How is the average atomic mass
calculated?
The abundance of each isotope is changed to decimal form.
The mass of each isotope is multiplied by it’s corresponding
decimal percentage. All the values are added together to
determine the average atomic mass
0.989 x 12 = 11.868
0.0101 x 13= + 0.143
12.01