Download Unit III * Introduction to Atomic Theory

Unit 2: Atomic Structure and
Nuclear Chemistry
Chemistry I
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.
What discoveries lead to the Atomic Theory?
• Atom:
– 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
John Dalton – Father of the Modern Atom
•
•
1808
Four Statements
1.
2.
3.
4.
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.
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 10-11 m – 2 x 10-10 m
50 – 200 pm (picometer)
Example 1
Subatomic Particles
•
•
•
•
Electrons
Protons
Neutrons
Nucleus
Electrons
• J.J. Thomson – 1897
• Discovered the electron using a cathode ray
tube (CRT)
• Negatively charged particles
Protons
• E. Goldstein – 1886
• Discovered the proton by careful observations
of another ray in the Cathode Ray tube
• Positively charged particles
Neutrons
• James Chadwick – 1932
• Discovers the neutron
• Neutrons are the “glue” that holds the nucleus
of the atom together.
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)
“Plum Pudding Model”
• Electrons evenly distributed
in an atom filled with
uniform positive chare
• First Atomic Model
• Example
The Atomic Nucleus
•
•
Ernest Rutherford – 1911
Using the “Gold Foil” experiment, Rutherford
determines:
1.
2.
3.
4.
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
Atomic Particle Summary
Name
Electron
proton
neutron
Symbol
Charge
Mass
(amu)
e-
-1
0.000543
Practically 0
p+
+1
1
n
0
1
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
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
Mass#
• Shorthand notation Atomic# Symbol
– Example: Gold
197
79
Au
Number of Neutrons
Number of Neutrons = Mass # - Atomic #
Sample Problem 4.2
How many protons, electrons, and neutrons are
in each atom?
a. 9 Be
4
b.
20
10
c.
23
11
Ne
Na
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
Nuclear or Isotopic Symbols
• Examples
– Carbon -12
– Carbon -14
• Nuclear Symbol:
Name - Mass #
• Isotopic Symbols
– 12C
Mass Number
6
–
14
6
C
Atomic Number
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
Sample Problem 4.5
• Element X has two naturally occurring isotopes. The isotope
with a mass of 10.012 amu has a relative abundance of
19.91%. The isotope with a mass of 11.009 amu has a
relative abundance of 80.09%. Calculate the atomic mass of
element X.
Chapter 25: Nuclear Chemistry
Regular Chemistry
• Deals with the arrangement
of atoms to form
compounds
• Never about the changing
of the nucleus
• Elements NEVER change to
other Elements
Nuclear Chemistry
• Deals with the decay of
unstable isotopes to form
a stable nucleus
• About the changing of the
nucleus
• Elements CAN change to
other Elements
25.1 Nuclear Radiation
• Radiation
– 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
Types of Radiation
Property
Composition
Alpha
Beta
Gamma
Alpha Particle
(helium nucleus)
Beta Particle
(electron)
High-Energy
Radiation
Symbol
α
β
γ
Charge
2+
1-
0
Mass (amu)
4
1/1840
0
Low
Tissue Paper
(0.05 mm)
Moderate
Skin or Foil
(4 mm)
Very high
Lead/Concrete
Entire body
Penetrating Power
Radiation Examples
• Alpha 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
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!!
Band of Stability
1:1
Ratio Line
Band of Stability
Most common transformation particles
Radiation Name
Symbol & Iso. Notation
Alpha particle
α,
Beta particle
β
Gamma radiation
γ
Positron
β+
0
1
Neutron
n
1
0
n
Proton
p+
1
1
p
4
2
Charge
Mass
+2
~4 amu
e
-1
1/1840amu (nothing)
“none”
0
0
e
+1
1/1840amu (nothing)
0
~1 amu
+1
~1 amu
He
0
1
Nuclear Stabilization Equations
• Alpha emission:
Uranium-238
• Beta emission:
Carbon-14
• Positron emission:
Oxygen-15
• Neutron emission:
Silver-107
U 24He  234
90Th
238
92
C 10 e147N
14
6
O10 e157N
15
8
107
47
Ag  n  Ag
1
0
106
47
Additional Example
• Beta Absorption of Krypton - 81
Transformation Examples
Silicon-27  ______ + β
27
14
Si  P  e
27
15
0
1
Bismuth-214  _____ + α
214
83
Bi  Tl  He
210
81
4
2
Aluminum-27 + α  Silicon-30 + ____
27
13
Al  He  Si  p
4
2
30
14
1
1
25.3 Fission and Fusion
• Fission:
– Large nucleus breaking down into smaller nuclei
• Fusion:
– Smaller nuclei combining to larger nucleus