3 Parts of the Atom:
Subatomic
Particle
Proton
Relative Mass
Charge
Where Found
1
+1
In Nucleus
Neutron
1
0(neutral)
In Nucleus
Electron
0
-1
Outside
nucleus in
electron cloud
How many electrons can each energy
level hold?
• 1st—2
• 2nd—8
• 3rd—18
• 4th –32
John Dalton: early 1800’s
Dalton’s 4 Points:
1. All elements are composed of indivisible and
indestructible atoms.
2. Atoms of the same element are identical.
3. Atoms of different elements are different.
4. Compounds are formed from the joining of
the atoms of 2 or more elements.
JJ Thomson--1897
Plum Pudding Model
But the
atom is
Neutral!!!!
While studying electric
discharge in Cathode-ray
tubes, Thomson
discovered the electron!!!
Ernest Rutherford--1908
Rutherford’s Gold Foil Experiment
In an attempt to build on Thomson’s
model, I discovered some amazing
stuff!!!
What
Rutherford
Expected
Actual
Results
Rutherford’s
Model
Notice 2 things:
1. Atom is made
up of mostly
empty space.
2. Electrons are
scattered
randomly!
Rutherford’s Atomic Model
Rutherford discovered the nucleus!!
Nucleus
Electrons
Neils Bohr--1913
Bohr “Planetary” Model of the Atom
The Bohr Model has the following features:
1. There is a nucleus(Rutherford’s Discovery)
2. The electrons move about the nucleus in “stationary, stable
states”(later referred to as orbits)!
The Wave Model of the Atom
Atomic Number
Chemical Symbol
Element Name
Average Atomic Mass
Atomic #
• # of protons in an atom
 In a neutral Atom, # of protons=# of
electrons
 Atomic # of a given element will never
change, therefore, the # of protons of an
element will not change.
Mass #
• Sum of the protons and neutrons
– Closest whole # to the Avg. Atomic Mass(from
periodic table)
Average Atomic Mass
• Mass of atom in Atomic Mass Units
i. Given on periodic table as average mass
of all isotopes of that element.(we’ll
discuss isotopes)
ii. Atomic Mass Unit—defined as 1/12 the
mass of a Carbon-12 atom
Isotopes
• Atoms of the same element with the same #
of protons, but different # of neutrons.
2 ways of writing Isotopes
H-1 H-2 H-3
• Each of these
represents Hydrogen
• The number represents
the mass #
• Each of these represents
Carbon
• The top # represents the
mass #
• The bottom # represents
the Atomic #
Ions
A “charged” atom.
– Atoms become charged by gaining or losing electrons.
2 Types of Ions:
1. + ions
2. - ions
Atoms become (+) Atoms become (-)
by losing electrons by gaining electrons
Atomic #
Atomic Mass
A # = 11
M # = 23
# p = 11
# e = 11
# n = 12
M#=#p+#n
23 = 11 + #n
Atomic #
Atomic Mass
A # = 19
M # = 39
# p = 19
# e = 19
# n = 20
M#=#p+#n
39 = 19 + #n
•This is the model of the atom as we know it today!!!!
•Does anything strike you as odd?
•Knowing what you have learned at this point, is this what you would
expect?
•Think in terms of electricity!!
•Does that change your thoughts any???
Forces within the Atom
1. ELECTROMAGNETIC FORCES
• Holds electrons in orbit around nucleus!!
• Electrons are kept in the orbit around the
nucleus by the electromagnetic force, because
the nucleus in the center of the atom is
positively charged and attracts the negatively
charged electrons.
If all the protons inside
the nucleus are the
same charge and repel,
what keeps them from
bursting and exploding
the atom? ? ? How do
they stay together? ? ?
2. Strong Force
• The strong forces oppose the
electromagnetic force of
repulsion between protons. Like
”glue” the strong force keeps the
protons together to form the
nucleus.
• The strong forces and
electromagnetic forces both
hold the atom together.
3. Weak Force
• Weak forces are
important because they
are responsible for
stabilizing particles
through the process of
radioactive decay, in
which a neutron in the
nucleus changes into a
proton and an electron.
4. Gravity
• mentioned last, is it
the “weakest”!
• Inside the tiny nucleus
of an atom, the effect
of gravity is small
compared to the
effects of the other
three forces.
Which force within the atom keeps the
electrons in orbit around the nucleus?
A.
B.
C.
D.
Strong Force
Weak Force
Electromagnetic Force
Gravity
Which force within the atom keeps
protons glued inside the nucleus?
A.
B.
C.
D.
Strong Force
Weak Force
Electromagnetic Force
Gravity
Which force within the atom is
responsible for radioactive decay?
A.
B.
C.
D.
Strong Force
Weak Force
Electromagnetic Force
Gravity
1. Alpha decay
2. Beta Decay
3. Gamma Decay
•In alpha decay, one radioactive nucleus is converted to
another with atomic # decreased by 2 and Mass #
decreased by 4
•An Alpha particle is a Helium nucleus!!
•In Beta decay, one radioactive nucleus is converted to
another with the atomic # increased by one and the mass #
left unchanged!
•In basic beta decay, a neutron is turned into a proton
and an electron. The electron is then emitted.
•A beta particle is an electron!!
Gamma Decay
•Gamma decay occurs because the nucleus is at too high an
energy. The nucleus falls down to a lower energy state and,
in the process, emits a high energy photon known as a
gamma particle.
•A gamma particle is a high energy photon(electromagnetic
radiation)
Penetrating Power
Which particle has the most
penetrating power?
A.
B.
C.
D.
Alpha particle
Beta particle
Gamma particle
Zeta particle
Which particle has the least
penetrating power?
A.
B.
C.
D.
Alpha particle
Beta particle
Gamma particle
Zeta particle
Nuclear Fission vs. Nuclear Fusion
• Nuclear Fission—big to small
• Nuclear Fusion—small to big
• Both release large amounts of energy!!
Nuclear Fission
• Nuclear fission involves the splitting of one
nucleus into 2 smaller nuclei.
Nuclear Fission at work!!!!
Nuclear Fusion
Nuclear Fusion involves the joining of 2 smaller
nuclei into one larger nucleus
Nuclear Fusion
Discuss Nuclear
Waste
Copy Summary
Statements:
p. 540, p. 545, p. 550
and p. 556