1. How Atoms Differ
Chp 4

3. Element
# protons
# electrons
# neutrons
Atomic number Pb 8 30

4. Element
# protons
# electrons
# neutrons
Atomic number Pb 82
125 O 8 Zn 30 35

5. Dalton was incorrect
1. Subatomic particles exist (atoms ARE divisible ).
2. Isotopes exist (atoms of an element ARE NOT identical).
Atoms with the same number of protons
(and electrons) but different number of neutrons are called isotopes.

6. C carbon-13 Atomic mass-number of protons and neutrons for the isotope6
carbon-13
Atomic number-number of protons for the isotope
Name of the isotope. Includes the mass number

7. Isotope Element
Atomic number
Mass number
Neon 10 22 Ne 22 10
Neon-22

8. Making life easier! 1 amu= 1/12th the mass of a carbon-12 atom.
1 amu =1 proton or neutron.

9. The atomic mass is the weighted average mass of isotopes of that element.
not a whole number?!
Natural percent abundance-the percentage that isotopes naturally occur in the environment. These percentages are used to calculate the weighted average of isotopes present in the environment.

10. Calculate the Student’s final grade-a weighted average
A=4.0, B=3.0, and C=2.0
B-Term Paper?(20% of grade)
C-Midterm exam (30% of grade)
B-Final Exam?(50% of grade)

11. Calculate the Atomic Weight for this isotope.
Chlorine-35  amu=34.969   Percent Abund.=75.78%
Chlorine-37  amu=36.966   Percent Abund. =24.22%

12. Calculate the atomic mass of unknown element X
Calculate the atomic mass of unknown element X. Identify the unknown element.
Isotope X-6 ? amu %
Isotope X-7 ? amu

13. Nitrogen has two naturally occuring isotopes
Nitrogen has two naturally occuring isotopes. Nitrogen-14 and Nitrogen-15.
Its atomic mass is amu. Which isotope of nitrogen is more abundant? Explain your answer.

14. Answers: 2.7 is a C 35.45 amu 6.94 amu is Lithium
Nitrogen-14 because its atomic mass is closest to the weighted average.