1. Atomic Number and Mass Number
The Atom
Atomic Number and Mass Number
Isotopes

2. Atomic Theory Atoms are building blocks of elements
Similar atoms in each element
Different from atoms of other elements
Two or more different atoms bond in simple ratios to form compounds

3. Subatomic Particles Particle Symbol Charge Relative Mass
Electron e
Proton p
Neutron n

4. Location of Subatomic Particles
10-13 cm
electrons
protons
neutrons
10-8 cm
nucleus

5. Atomic Number
Counts the number of
protons
in an atom

6. Periodic Table Represents physical and chemical behavior of elements
Arranges elements by increasing atomic number
Repeats similar properties in columns known as chemical families or groups

7. Periodic Table 11 Na

8. Atomic Number on the Periodic Table11 Na
Atomic Number
Symbol

9. All atoms of an element have the same number of protons11 Na
11 protons
Sodium

10. Learning Check AT 1
State the number of protons for atoms of each of the following:
A. Nitrogen
1) 5 protons 2) 7 protons 3) 14 protons
B. Sulfur
1) 32 protons 2) 16 protons 3) 6 protons
C. Barium
1) 137 protons 2) 81 protons 3) 56 protons

11. Solution AT 1
State the number of protons for atoms of each of the following:
A. Nitrogen
2) 7 protons
B. Sulfur
2) 16 protons
C. Barium
3) 56 protons

12. Number of Electrons An atom is neutral The net charge is zero
Number of protons = Number of electrons
Atomic number = Number of electrons

13. Mass Number
Counts the number of
protons and neutrons
in an atom

14. Atomic Symbols atomic number 11 Show the mass number and atomic number
Give the symbol of the element
mass number
23 Na sodium-23
atomic number 11

15. 16 31 65 8 15 30 More Atomic Symbols O P Zn 8 p+ 15 p+ 30 p+
O P Zn
8 p p p+
8 n 16 n 35 n
8 e e e-

16. Isotopes
Atoms with the same number of protons, but different numbers of neutrons.
Atoms of the same element (same atomic number) with different mass numbers
Isotopes of chlorine
35Cl 37Cl
chlorine chlorine - 37

17. Questions 2
Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.
12C C 14C
#P _______ _______ _______
#N _______ _______ _______
#E _______ _______ _______

18. Solutions 2 6 6 6 12C 13C 14C #P __6___ _ 6___ ___6___
#P __6___ _ 6___ ___6___
#N __6___ _ _7___ ___8___
#E __6___ _ 6___ ___6___

19. Questions 3 An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) ) ) 65
B. Number of neutrons in the zinc atom
C. What is the mass number of a zinc isotope
with 37 neutrons?
1) ) ) 67

20. Solutions 3 An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
B. Number of neutrons in the zinc atom
2) 35
C. What is the mass number of a zinc isotope
with 37 neutrons?
3) 67

21. Questions 4 Write the atomic symbols for atoms with the following:
A. 8 p+, 8 n, 8 e- ___________
B. 17p+, 20n, 17e- ___________
C. 47p+, 60 n, 47 e- ___________

22. Solutions 4 B. 17p+, 20n, 17e- 37Cl 17 47 16O A. 8 p+, 8 n, 8 e- 8
C. 47p+, 60 n, 47 e- 107Ag 47

23. Questions 5 16 14 14 An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) ) ) 34
B. Its mass number is
C. The element is
1) Si 2) Ca 3) Se
D. Another isotope of this element is
1) 34X 2) 34X 3) 36X

24. Solutions 5 14 An atom has 14 protons and 20 neutrons.
A. It has atomic number
1) 14
B. It has a mass number of
3) 34
C. The element is
1) Si
D. Another isotope of this element would be
3) 36X 14

25. Masses of Atoms
A scale designed for atoms gives their small atomic masses in atomic mass units (amu)
An atom of 12C was assigned an exact mass of amu
Relative masses of all other atoms was determined by comparing each to the mass of 12C
An atom twice as heavy has a mass of amu. An atom half as heavy is 6.00 amu.

26. Na 22.99 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

27. Questions 6
Using the periodic table, specify the atomic mass of each element (round to the tenths place):
A. calcium __________
B. aluminum __________
C. lead __________
D. barium __________
E. iron __________

28. Solution AT6
Using the periodic table, specify the atomic mass of each element (round to the tenths place):
A. calcium _40.1 amu _
B. aluminum _27.0 amu _
C. lead _207.2 amu_
D. barium _137.3 amu_
E. iron _55.8 amu__

29. Calculating Atomic Mass
Percentage (%) abundance of isotopes
Mass of each isotope of that element
Weighted average =
mass isotope1(%) + mass isotope2(%) + …

30. Atomic Mass of Magnesium
Isotopes Mass of Isotope Abundance
24Mg = 24.0 amu %
25Mg = amu %
26Mg = amu %
Atomic mass (average mass) Mg = 24.3 amu Mg
24.3

31. Questions 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 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium?

32. Solutions 7 Atomic mass Ga = 69.7 amu
68.9 amu x = amu for 69Ga
100
Ga-71 (%/100)
70.9 amu x = amu for 71Ga
Atomic mass Ga = amu

33. Finding An Isotopic Mass
A sample of boron consists of 10B (mass 10.0 amu) and 11B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?

34. Assign X and Y values:
X = % 10B Y = % 11B
Determine Y in terms of X
X Y = 100
Y = X
Solve for X:
X (10.0) (100 - X )(11.0) =
Multiply through by 100
10.0 X X =

35. Collect X terms
10.0 X X =
- 1.0 X = -20
X = = % 10B
- 1.0
Y = X
% 11B = % = 80% 11B

36. Questions 8
Copper has two isotopes 63Cu (62.9 amu) and 65Cu (64.9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass)
1) 30% 2) 70% 3) 100%

37. Solutions 8 2) 70% Solution 62.9X + 6490 = 64.9X = 6350 -2.0 X = -140
2) 70%
Solution
62.9X = 64.9X = 6350
-2.0 X = -140
X = 70%