© 2004 Pearson Education Inc.,
publishing as Addison-Wesley
Atom
electron
nucleus
p+n
proton
neutron
e-
An atom
consists of a
small, dense
nucleus
surrounded
by electrons
The “size” of an Atom
• Although it is the smallest part of the atom, most of
the atom’s mass is contained in the nucleus.
• The electrons do not “orbit” the nucleus; they are
“smeared out” in a cloud which give the atom its size.
Hydrogen
p+
e-
atomic number = 1
atomic mass number = 1
Helium
p+p+
n n eeatomic number = 2
atomic mass number = 4
Hydrogen
Deuterium
isotope
p+
n
atomic number = 1
atomic mass number = 2
e-
The particles in the nucleus determine the
element & isotope.
atomic number = #protons
atomic mass no. = #protons + #neutrons
Note on Energy on Atomic Scales:
We use a smaller unit of Energy on quantum scales..
The electron-volt (eV) = 1.602x10-19 J
=0.0000000000000000001602 J
This is because atomic energies are incredibly small…
for a typical football player:
K  1/2 mv 2  (1 / 2)(90 kg)(10m / s) 2  4500 J
1


22
 (4500 J )
eV/J

2
.
808

10
eV

19
 1.602 10

n
En (eV)
1
-13.60
2
-3.40
3
-1.51
4
-0.85
5
-0.38
…
…
En = -13.6 / n2
Hydrogen
n=1
n=3
n=4
n=2
What if an electron is missing?
ion
e-
p+p+
nn
atomic number = 2
atomic mass number = 4
4
2
He
+1
What if two or more atoms combine to form
a particle?
molecule
p+
8p+
8n
p+
H2O (water)
Phases of Matter
• the phases
–
–
–
–
solid
liquid
gas
plasma
depend on how tightly
bound the atoms and/or
molecules are
• As temperature increases,
these bonds are loosened:
Phases of Matter
• the phases
–
–
–
–
solid
liquid
gas
plasma
depend on how tightly
bound the atoms and/or
molecules are
• As temperature increases,
these bonds are loosened:
Electron Energy
• Electrons that are bound in atoms can gain or lose
energy.
• When electrons have the lowest energy possible, we say
the atom is in the ground state.
• When electrons have more energy than this, the atom is
in an excited state.
• When electrons gain enough energy to escape the
nucleus, the atom is ionized.
Electron Energy Levels
• Electrons can not have just any energy while orbiting
the nucleus.
• Only certain energy values are allowed.
• Electrons may only gain or lose specific amounts of
energy.
0.0
eV
-0.85 eV
-1.51 eV
-3.40 eV
-13.60 eV
• Each element (atom and ion)
has its own distinctive set or
pattern of energy levels.
• This diagram depicts the
energy levels of Hydrogen.
n=2
n=3
Photons are created when an electron jumps from one energy level to
another
Important years for astronomy
n
En (eV)
1
-13.60
2
-3.40
3
-1.51
4
-0.85
5
-0.38
(Rydbergs formula)
…
…
DE(3
En = -13.6 / n2 (eV)
) = E3-E2 =-1.51-(-3.40) = 1.89 eV
g2
Objects in Motion
• speed – rate at which an object moves, i.e. the
distance traveled per unit time [m/s; mi/hr]
• velocity – an object’s speed in a certain
direction, e.g. “10 m/s moving east”
• acceleration – a change in an object’s velocity,
i.e. a change in either speed or direction is an
acceleration [m/s2]
• As objects fall, they
accelerate.
• The acceleration due
to Earth’s gravity is
10 m/s each second,
or g = 10 m/s2.
• The higher you drop
the ball, the greater
its velocity will be at
impact.
t=0s;
v=0m/s
t=1s;
v=10 m/s
You may remember
my experiment…
t=2s;
v=20m/s
The Acceleration of Gravity (g)
• Galileo measured g to be about 10 m/s2
• He demonstrated that g is the same for all objects,
regardless of their mass!
• This was confirmed by the Apollo astronauts on the
Moon, where there is no air resistance.
Galileo was right!
Universal Laws of Motion
“If I have seen farther than others, it
is because I have stood on the
shoulders of giants.”
Sir Isaac Newton (1642 – 1727)
Physicist
Sir Isaac Newton (1642-1727)
• Perhaps the greatest
genius of all time
• Invented the reflecting
telescope
• Invented calculus
• Connected gravity and
planetary forces
Philosophiae naturalis
principia mathematica
Forces
• Forces change the motion of objects.
• As long as the object’s mass does not change,
the force causes a change in velocity, or an…
Newton’s Laws of Motion
A body at rest or in motion at a
constant speed along a straight line
remains in that state of rest or motion
unless acted upon by an outside force.
Newton’s Laws of Motion
The change in a body’s velocity due
to an applied force is in the same
direction as the force and
proportional to it.
F
a
a
The proportionality constant is mass:
F=ma
Gravity:
F = mg
g is the gravitational acceleration (9.8 m/s2)
Gravitational Potential Energy
E = F n h = mg n h
m
g
h
Newton’s Laws of Motion
For every applied force, a force of
equal size but opposite direction
arises.
Newton’s Laws of Motion
Is Mass the Same Thing as Weight?
• mass – the amount of matter in an object
• weight – a measurement of the force which
acts upon an object
When in “free-fall,”
you are weightless!!
Forces
• Forces change the motion of objects – cause
accelleration.
• momentum – the (mass x velocity) of an
object
p = mv
[kg m/s]
• force – anything that can cause a change in
an object’s momentum
F = D(mv) = mDv = ma [kg m/s2 =N]
Escape velocity !
• Can an object escape the gravitational
attraction of the Earth?
• Does it have enough kinetic energy to
overcome the gravitational potential
energy of the Earth?
mgh I ½ mv2 ????