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```									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)
These symmetries
are responsible for
the symmetry in the
bonding of solids!
Summary: Atomic models

Greek
Jellium
Planetary
Bohr (Quantum)
Modern Quantum
Scientific Notation

How do we write 1,000,000,000,000,000,000 in a
more compact form?

1,000,000,000,000,000,000
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
2.

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 …
Charges Revisited

[1] It comes it two types: positive and negative.
[2] Charge is conserved.
[3] Like charges repel; opposites attract.
[4] It only comes in discrete amounts (the
amount that comes with an electron).
Materials:

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.
Conductors

Describe the forces between
the two charges.                           +
-

Since unlike charges attract, the
electrostatic force will try to pull
them together.

How will the charges MOVE if the material is an
insulator?
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               -
conducting material.

Like charges repel so the two
charges will repel one another.

How will the charges MOVE?

They will move away from one
another.                              -
-
Where will the charges end up?
-
-

A                            C
-
-
-
-
B                             D
-
-            -
-
WHY do the charges end up in
this configuration??

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
go??
-
-
They should end up somewhere
on the outer perimeter—this
will maximize the distance          -
between them.
-

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
charges?

Again, the charges will configure       -   -
themselves to maximize the distance
from each of the other charges. The
-   -
results in them being an equidistance
apart.
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!!

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