The Modern Quantum Description of the Atom
What does the atom really look like? Do the
electrons really orbit like the planets?
No. The negative charge the electrons carry
looks smeared out—or like a cloud.
Another possible formation: (note: this is ONE electron)
Other possible configurations (or symmetries)
are responsible for
the symmetry in the
bonding of solids!
Summary: Atomic models
How do we write 1,000,000,000,000,000,000 in a
more compact form?
There are 18 zeros
We write this as 1 x 1018
How do we write 1,200,000,000,000,000,000?
Again there are 18 spots
after the first number, but
we have to account for the
Answer: 1.2 x 1018
What is (1.82 x 1012) x (3.87 x 109)?
Step 1: group the numbers as follows
(1.82 x 3.87) x (1012 x 109)
Step 2: multiply these: 7.04
Step 3: add the exponents of the 10’s: 21
Step 4: Write the result: 7.04 x 1021
What is (2.4 x 1020) / (1.6 x 1011)?
Step 1: (Group) (2.4/1.6) x (1020 / 1011)
Step 2: (Divide numbers): 1.5
Step 3: SUBTRACT exponents: 9
Step 4: Write in scientific notation
1.5 x 109
What is 0.0000000000005 in scientific notation?
There are 13 digits. Thus we can
write this as 5.0 x 10-13
What is (3.0 x 1012) x (2.0 x 10-4)? 6.0 x 108
What is (6.0 x 104) / (3.0 x 10-3)? 2.0 x 107
And now to use scientific notation …
 It comes it two types: positive and negative.
 Charge is conserved.
 Like charges repel; opposites attract.
 It only comes in discrete amounts (the
amount that comes with an electron).
Conductors: materials where the electrons are free to
move through the material. Examples include metals
(like wires), salt water, etc.
Insulators: Electron are NOT free to move through
the material. Examples include rubber, plastic,
wood, coatings on electrical cords, etc.
Describe the forces between
the two charges. +
Since unlike charges attract, the
electrostatic force will try to pull
How will the charges MOVE if the material is an
They will NOT move—the electrons
can’t move in an insulating material.
How will the charges move if +
the material is a conductor? -
They will move towards
one another. + -
Describe the force between two -
negative charges placed in a -
Like charges repel so the two
charges will repel one another.
How will the charges MOVE?
They will move away from one
Where will the charges end up?
WHY do the charges end up in
They want to maximize the - -
distance between them.
Now suppose that we have a
metal ball with two electrons
in it. Where do the electrons
They should end up somewhere
on the outer perimeter—this
will maximize the distance -
Now suppose that we add a third
electron—where will the three of -
them end up?
They will end up equidistant
from each other, but at the same -
time maximizing the distance
from one another.
What if there are FOUR
Again, the charges will configure - -
themselves to maximize the distance
from each of the other charges. The
results in them being an equidistance
What if there are 1 x 1015 “free” electrons
in a conductor—where do they end up?
They end up spread out evenly on the SURFACE
of the conducting material!!