Chemistry

1. Atomic MASS
General chemistry 1

2. At the end of the lesson, the learners shall be able to:
1. Define atomic mass unit;
2. Calculate the average atomic mass of elements;
3. Determine the average molecular mass of molecules; and
4. Determine the average formula mass of ionic compounds.
Objectives

3. Key words and concepts to be learned

4. What are
isotopes?

5. What are
isotopes?

7. Can you count
objects by weighing
them?

12. What is atomic
mass and Atomic
mass unit?

14. https://www.youtube.com/watch?v=KuyB-445gQM

16. The atomic mass of Cu-63 is 62.93 amu. This
means that relative to C-12, one atom of Cu-63 is
62.93/12 or 5.244 times the mass of a C-12 atom.

17. The atomic mass of Cu-63 is 62.93 amu. This
means that relative to C-12, one atom of Cu-63 is
62.93/12 or 5.244 times the mass of a C-12 atom.

18. TRY this..
One atom of Se-77 is 6.410 times as
heavy as an atom of C-12. What is the
atomic mass of Se-77?

19. TRY this..
One atom of Se-77 is 6.410 times as
heavy as an atom of C-12. What is the
atomic mass of Se-77?
Answer : 6.410 x
12 amu = 76.92
amu

20. Average Atomic
MASS

22. For carbon, the natural abundance of C-12 is 98.90% while that of C-13 is
1.10%. The atomic
mass of C-13 has been determined to be 13.00335 amu while that of C-12 is
exactly 12 amu.
Now, we calculate the average atomic mass of carbon:
= (atomic mass of C-12) (% abundance of C-12) + (atomic mass of C-13) (%
abundance of C-13)
= (12.0000 amu) (.9890) + (13.00335 amu) (.0110)
= 12.01 amu

23. PRACTICE
EXERCISES:
1. From the periodic table, look up the average atomic mass of the following
elements: Co, Be,
Al, Zn.
2. Copper has two stable isotopes with the following masses and % abundances:
Cu-63 (62.93
amu, 69.09% abundance) and Cu-65 (64.9278 amu, 30.91% abundance).
Calculate the
average atomic mass of copper.

24. PRACTICE
EXERCISES:
3. An element consists of an isotope with mass of 10.0129 amu and 19.91%
abundance, and
another isotope with mass of 11.0093 amu and 80.09% abundance. Calculate the
average
atomic mass of this element. Refer to the periodic table and identify the element.

25. PRACTICE
EXERCISES:

26. Average Molecular Mass (also referred
to as molecular mass)
molecular mass - is the sum of the average atomic
masses of the atoms in the molecule.

27. Average Molecular Mass (also referred
to as molecular mass)
molecular mass - is the sum of the average atomic
masses of the atoms in the molecule.

28. Average Formula Mass (also referred to
as formula mass)
formula mass - is the sum of the atomic masses of
the atoms in the ionic compound.

29. Average Formula Mass (also referred to
as formula mass)
formula mass - is the sum of the atomic masses of
the atoms in the ionic compound.

30. Assignment: