1. Chapter 4
The Atom – Part 2

2. Subatomic Particles PARTICLE SYMBOL CHARGE MASS (amu or u ) LOCATION
electron e- -1 0
orbit nucleus
proton p+ +1 1
inside nucleus
neutron n0

3. Alchemy “The Golden Rule”

4. The number of protons in the nucleus of the atom (atomic number = Z) determines the atoms identity
Gold Atom Lead Atom

5. Mass Number
The sum of the protons and neutrons in the nucleus of an atom.

6. What element is represented below?

7. Carbon - 12 This is the symbol for the isotope carbon-12.
Atomic number is 6.
Mass number is 12.

8. Carbon has 3 Isotopes

9. Isotopes Isotopes are atoms of the same element with different masses.
Isotopes are atoms of an element that have the same number of protons in the nucleus, but a different number of neutrons in the nucleus.
Isotopes therefore have the same atomic number but different mass numbers.
There are 275 isotopes of the 81 stable elements, in addition to over 800 radioactive isotopes, and every element has known isotopic forms.
Isotopes of a single element possess almost identical properties.

10. Carbon - 12
Write the symbols for carbon-13 and carbon-14.

11. The Discovery of Isotopes
John Dalton thought all atoms of the same element were identical.
The discovery of isotopes changed this idea.

12. What is the average mass of a carbon atom?
12.01

13. Atomic Mass The atomic mass of carbon is 12.01 amu.
Atomic mass is the average mass of all the isotopes of an atom. It takes into account the different isotopes of an element and their relative abundance.

14. the atomic weight of Cl = 35.5 amu
What is the average atomic weight for chlorine if it has two isotopes? The percent abundance for chlorine-35 is 75.53%. The percent abundance for chlorine-37 is 24.40%. The mass for Cl-35 is 35.0 amu and for Cl-37 it is 37.0 amu.
[(0.7553)(35.0 amu)] + [(0.2440)(37.0 amu)]
= [ ] + [9.028] =
the atomic weight of Cl = 35.5 amu

15. What is the average atomic mass for thallium, Tl
What is the average atomic mass for thallium, Tl? The two stable isotopes and their abundances are listed here.Tl-205 has a mass of amu with an abundance of % and Tl-203 has a mass of amu with an abundance of % .
204.5 amu

16. the atomic weight of Tl = 204.5 amu
What is the average atomic mass for thallium, Tl? The two stable isotopes and their abundances are listed here.Tl-205 has a mass of amu with an abundance of % and Tl-203 has a mass of amu with an abundance of % .
[(0.7048)( amu)] + [(0.2952)( amu)]
= [ ] + [59.943] =
the atomic weight of Tl = amu

17. Common Uses of Isotopes
Isotope Analysis
Radiometric Dating
Nuclear Medicine:
Magnetic Resonance Imaging (MRI)
Positron Emission Tomography (PET scans)

18. Importance of Isotopes

19. Radiometric Dating

20. Half-Life The decay of radioactive elements occurs at a fixed rate.
The half-life of a radioactive isotope is the time required for one half of the material to degrade into a more stable material.
Although the half-life pattern is the same for every radioactive isotope, the length of a half-life is different.
For example, C-14 has a half-life of about 5730 years while Ir-192 has a half-life of about 74 days.

21. Half-Life

22. Carbon Dating (2:11)

23. Nuclear Medicine refers to imaging techniques that use radioactive isotopes to detect and treat disease. Magnetic resonance imaging (MRI) and positron emission tomography (PET scans) are examples.

24. MRI PET scan

25. An atom of vanadium contains 23 electrons
An atom of vanadium contains 23 electrons. How many protons does it contain?
23 p+

26. An atom of silver contains 47 protons. What is its atomic number?

27. An “atom” of sodium contains 11 electrons. What is its atomic number?

28. An atom contains 37 protons. What element is it?
rubidium

29. How many electrons, protons and neutrons are in an atom of actinium with a mass number of 221?

30. How many electrons, protons and neutrons are in an atom of rhodium-105?

31. Homework
Chapter 4 Worksheet 1 (due in two days).