Isotopes and Mass Number

1
Isotopes and Mass Number

• How Daltons atomic theory was wrong
• Atoms ARE divisible. (Who is credited with first
  splitting an atom?)
• All atoms of a particular element are NOT
  identical.
• All atoms of an element do have the same number
  of protons and electrons, so what could differ?

2
Isotopes and Mass Number (cont.)

• Isotopes atoms with the same number of protons
  (same element), but with different numbers of
  neutrons.
• Examples
• Potassium (K) K-39, K-40, K-41
• Chlorine (Cl) Cl-35 and Cl-37
• Uranium U-235 and U-238

3
Isotopes and Mass Number (cont.)

• If atoms have the same number of protons and
  electrons, but different numbers of neutrons,
  what else will be different?
• Answer MASS
• Mass number number of protons number of
  neutrons

4
Isotopes and Mass Number (cont.)

• Examples
• K-39 19 protons 20 neutrons
• K-40 ___ protons ___ neutrons
• K-41 ___ protons ___ neutrons
• Isotope symbolic notation
• mass number Element Symbol 39K
• atomic number
  19
• Isotope name is potassium-39

5
Isotopes and Mass Number (cont.)

• Review
• Number of protons is the same for all atoms of a
  particular element
• Number of neutrons can vary ( isotopes)
• What is the mass number?
• What is the atomic number?
• Number of neutrons ?

6
Isotopes and Mass Number (cont.)

• Number of neutrons mass number atomic number
• Example If an atom of neon has an atomic number
  of 10, and a mass number of 22
• How many protons? Neutrons? Electrons?
• What is the NAME of the isotope?
• What is the SYMBOL of the isotope?

7
Practice Assignment

• Practice p.101 (14)
• Study Guide Workbook pp. 21-22 (13-23)