1. Unit 2: Atomic Structure and Nuclear Chemistry
Chemistry I

2. Goals 1 – 3 Summarize Dalton’s atomic theory.
Distinguish among protons, electrons, and neutrons in terms of mass and charge.
Describe the structure of the atom.

3. What discoveries lead to the Atomic Theory?
Smallest particle of an element that retains the properties of the element
Democritus – Father of the Atom
400 B.C.
Atomos: Greek for “indivisible”
Philosophy – not Science
No measured or experimental support

4. John Dalton – Father of the Modern Atom
1808
Four Statements
All elements are composed of tiny indivisible particles called atoms.
Atoms of the same element are identical. Atoms of different elements are different.
Atoms combine in simple whole number ratios.
Atoms of one element are never changed to atoms of another element during chemical reactions.

6. Sizing up the Atom
What instruments are used to observe individual atoms?
Despite their small size, atoms are observable with scanning electron microscopes
Radii fall between 5 x m – 2 x m
50 – 200 pm (picometer)
Example 1

7. Subatomic Particles
Electrons
Protons
Neutrons
Nucleus

8. Electrons
J.J. Thomson – 1897
Discovered the electron using a cathode ray tube (CRT)
Negatively charged particles

9. Protons
E. Goldstein – 1886
Discovered the proton by careful observations of another ray in the Cathode Ray tube
Positively charged particles

10. Neutrons James Chadwick – 1932 Discovers the neutron
Neutrons are the “glue” that holds the nucleus of the atom together.

11. Subatomic Particles Electrons Protons Neutrons Nucleus Atomic Charges:
Neutral atom: Equal # of Protons and Electrons
Element dependant on # of Protons
Number of Electrons can change – creates charged atom (called IONs)

12. “Plum Pudding Model”
Electrons evenly distributed in an atom filled with uniform positive chare
First Atomic Model
Example

13. The Atomic Nucleus Ernest Rutherford – 1911
Using the “Gold Foil” experiment, Rutherford determines:
An atom is mostly space.
There is a nucleus in the middle of the atom containing the protons
The electrons orbit a large distance away from the nucleus.
Proposes a “Solar System” or “Orbital” model of the atom
Cute Summary of History

14. Name Symbol Charge Mass (amu)
Atomic Particle Summary
Name
Symbol
Charge
Mass
(amu)
Electron e- -1
Practically 0
proton p+ +1 1
neutron n

15. Atomic Number Number of protons in the nucleus of an atom
Each element has a unique atomic number
The number of electrons usually equals the atomic number in a neutral atom, but doesn’t need to

16. Mass Number The total number of protons and neutrons in an atom
Atoms of the same element can have different mass numbers
Mass number is NOT normally found on the periodic table
Shorthand notation
Example: Gold

17. Number of Neutrons
Number of Neutrons = Mass # - Atomic #

18. Sample Problem 4.2
How many protons, electrons, and neutrons are in each atom?

19. Isotopes
Atoms with the same number of protons, but different numbers of neutrons
Isotopes of an element have the same atomic number, but different mass numbers
Nuclear Symbol or Isotopic symbol: shows number of protons & mass number of an atom

20. Nuclear or Isotopic Symbols
Examples
Carbon -12
Carbon -14
Nuclear Symbol:
Name - Mass #
Isotopic Symbols
Mass Number
Atomic Number

21. Atomic Mass: A Weighted Average
Atomic Mass Unit: (amu)
Unit of mass for atomic nuclei
1 amu = 1/12 the mass of Carbon-12
Atomic Mass:
Weighted average mass of all the naturally occurring isotopes in a sample of an element

22. Sample Problem 4.5
Element X has two naturally occurring isotopes. The isotope with a mass of amu has a relative abundance of 19.91%. The isotope with a mass of amu has a relative abundance of 80.09%. Calculate the atomic mass of element X.

23. Chapter 25: Nuclear Chemistry
Regular Chemistry
Nuclear Chemistry
Deals with the arrangement of atoms to form compounds
Never about the changing of the nucleus
Elements NEVER change to other Elements
Deals with the decay of unstable isotopes to form a stable nucleus
About the changing of the nucleus
Elements CAN change to other Elements

24. 25.1 Nuclear Radiation Radiation Radioactive decay: Radioisotope:
The penetrating light rays and/or particles emitted by a radioactive source
Radioactive decay:
The spontaneous emission of radiation by an unstable nucleus
Radioisotope:
An isotope that has an unstable nucleus and undergoes radioactive decay

25. High-Energy Radiation
Types of Radiation
Property
Alpha
Beta
Gamma
Composition
Alpha Particle
(helium nucleus)
Beta Particle
(electron)
High-Energy Radiation
Symbol α β γ
Charge 2+ 1-
Mass (amu) 4
1/1840
Penetrating Power
Low
Tissue Paper
(0.05 mm)
Moderate
Skin or Foil
(4 mm)
Very high
Lead/Concrete
Entire body

26. Radiation Examples Alpha Radiation Beta Radiation Gamma Radiation
Uranium-238 to Thorium-234
Beta Radiation
Carbon-14 to Nitrogen-14
Summary: What has really happened?
Gamma Radiation
Thorium-230 to Radium-226
Thorium-234 to Protactinium-234

27. 25.2 Nuclear Transformations
Why does the nucleus stay together?
Strong Nuclear Force
Short range, attractive force that acts among nuclear particles
Neutrons and Protons attract one another!
Much stronger than electrical or gravitational force
Electromagnetic Force
Repulsive force between protons. Tries to pull the nucleus apart.
Stable Nucleus
Correct balance of Strong Nuclear & Electromagnetic Forces
Correct p+ to n ratio
MOST ATOMS ARE STABLE!!

28. Band of Stability
1:1
Ratio Line
Band of Stability

29. Most common transformation particles
Radiation Name
Symbol & Iso. Notation
Charge
Mass
Alpha particle α, +2
~4 amu
Beta particle β -1
1/1840amu (nothing)
Gamma radiation
γ “none”
Positron β+ +1
Neutron n
~1 amu
Proton p+

30. Nuclear Stabilization Equations
Alpha emission:
Uranium-238
Beta emission:
Carbon-14
Positron emission:
Oxygen-15
Neutron emission:
Silver-107

31. Additional Example
Beta Absorption of Krypton - 81

32. Transformation Examples
Silicon-27  ______ + β
Bismuth-214  _____ + α
Aluminum-27 + α  Silicon-30 + ____

33. 25.3 Fission and Fusion Fission: Fusion:
Large nucleus breaking down into smaller nuclei
Fusion:
Smaller nuclei combining to larger nucleus