1. SNC1D Isotopes

2. Isotopes
Isotopes are atoms of the same element that have a different number of neutrons.
All isotopes will have the same number of protons but different number of neutrons.
Carbon-12
Carbon-13
Carbon-14
Protons 6
Neutrons 7 8
Electrons

3. + + Carbon-12 Neutrons 6 Protons 6 Electrons 6 Carbon-14 Neutrons 8
Nucleus
Neutron
Proton +
Electrons
Nucleus
Nucleus
Neutron
Proton +
Carbon-12
Neutrons 6
Protons 6
Electrons 6
Electrons
Carbon-14
Neutrons 8
Protons 6
Electrons 6
Nucleus

4. Therefore the mass number of each isotope will be different.
Isotopes
Therefore the mass number of each isotope will be different.
Isotopes of the same element have the same chemical properties but could have slightly different physical properties.

5. Learning Check! 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

6. Write the atomic symbols for atoms with the following:
Learning Check!
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- ___________
168O
3717Cl
10747Ag

7. Learning Check! 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

8. Standard atomic notation
Isotopes of Hydrogen
Isotope #
protons
electrons
neutrons
Mass number
Standard atomic notation
Protium 1
11H
Deuterium 2
21H
Tritium 3
31H

9. Practice: How many neutrons are in each of the following isotopes?
Isotopes Notation
Isotopes can be indicated by writing the symbol or name of the element followed by a dash and the mass number (e.g. Carbon-14 or C-14)
Isotopes of chlorine
35 17 Cl 3717Cl
chlorine chlorine - 37
Practice: How many neutrons are in each of the following isotopes?
Cobalt-60
Iodine-131
Uranium-235

10. Uses of Isotopes Carbon-14 exists in a set ratio with Carbon-12
When the organism dies, C-14 decays, but C-12 does not
The percentage of C-14 decreases as the age of the dead organism increases. This percentage is used to estimate the age of the organism.

11. Standard atomic notation
Isotope
# protons
# electrons
# neutrons
Mass number
Standard atomic notation
Cl-37 17 20 37
3717Cl
Li-7 3 4 7
73Li
Mg-25 12 13 25
2512Mg
C-14 6 8 14
146C

12. An atom of 12C was assigned an exact mass of 12.00 amu
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.

13. 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

14. 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

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

16. Learning Check
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?

17. 68.9 amu x amu x
Atomic mass Ga = amu

18. 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?

19. Determine Y in terms of X
Assign X and Y values:
X = % 10B Y = % 11B
Determine Y in terms of X
X Y = 100
Y = X
Solve for X:
X (0.100) + (100 - X )(0.110) =
X = 0.20
= % 10B
Y = X
% 11B = % = 80% 11B

20. Copper has two isotopes 63Cu (62. 9 amu) and 65Cu (64. 9 amu)
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%