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A Brief History of Chem I
Differentiate between physical and chemical
characteristics; chemical change and a physical
change.
Define and give formulas where applicable:
density:
specific heat capacity:
mole:
molar mass (aka molecular weight):
-the amount of substance that contains as many
particles as there are atoms in exactly 12
grams of carbon-12.
-contains 6.022136736 x 1023 particles (aka
Avogadro’s number)
-the mass in grams of 1 mole of atoms of any
element or molecules of any compound is called
the molar mass, M (g/mol).
Kinetic-Molecular Theory: explains the physical
properties of matter. Matter consists of atoms
(pure element) and molecules (compounds or
polyatomic elements) which are in constant
motion.
SOLIDS: closely packed; vibrate; external
shape often indicates internal structures
(crystals, etc)
LIQUIDS: particles are further apart yet
still interact with each other constantly; no
specific shape; particles not confine to specific
locations.
GASES: particles very far apart and rarely
collide; very rapid movement; lowest density;
fill container; 1 mole of a gas at STP has a
volume of 22.4 L.
Regardless of state, increasing TEMPERATURE
will increase speed of particles.
At what point will all particles STOP moving?
What is this called?
Remember that chemistry uses SI units: kg, m,
s, K, mol, A (p35)
Common prefixes:
megakilodecicentimillimicronanopicoDimensional Analysis review:
How many mg in .034 kg?
1. Identify the needed conversion factors.
2. Set up equation so that units cancel out.
3. Record answer with correct sigfigs and
include final unit.
4. Determine if answer is reasonable.
(Leave room for practice problems.)
SigFig Review:
Precision (repeatability) vs Accuracy (closeness
to accepted value)
Why sigfigs?
A calculated result can be no more precise than
the least precise piece of information that went
into its calculation.
Sigfig rules:
1. All nonzero numbers are significant.
2. Zeros are NOT significant when:
-they trail in a number w/out a decimal.
-they are leading zeros
3. Zeros ARE significant when:
-they trail in a number with a decimal.
-they are “trapped” between two nonzero
numbers.
4. When adding or subtracting, keep only as
many places after the decimal as the starting
number with the fewest places after the
decimal.
5. When multiplying or dividing, keep as many
sigfigs in the answer as the contributing
number with the fewest sigfigs.
How many milliliters in .0167 L?
How many kg in 1240 mg?
How many km in 1345 cm?
How many grams are in 1.34 moles of Fe?
How many moles are in 255 g of C?
How many moles in 124 ml of mercury if its
density is 13.534 g/ml?
Waves and what they tell us about atoms…
For any electromagnetic wave,
v = c
 = c/v
v = c/
 = wavelength in meters
v = frequency in cycles per second, s-1, or hertz,
Hz
c = speed of light, 2.998 x 108 m/sec
Tip: always convert your wavelength to meters
first or your frequency to hertz.
E = nhv
E = energy change in Joules
n = number of photons or quanta (usually 1 for
one photon or 6.022 x 1023 for a mole of
photons)
h = Planck's constant, 6.626 x 10-34Js
v = frequency in cycles per second, s-1, or hertz,
Hz
Einstein proposed in his special theory of
relativity that energy does have mass and this
mass can be calculated by the following
equation. This was confirmed by Compton's
experimentation in the 1920's and 1930's.
E = mc2
E = energy in Joules
m = mass in grams
c = speed of light, 2.998 x 108 m/sec
Einstein's and Planck's work seemed to confirm
that light does indeed act like particulate
matter, particles with discriminate mass and
energy associated with them. Louis de Broglie
then worked on the idea that particulate
matter might also display the properties of
waves. He derived this formula:
 = _h_
mv
where
v = velocity in m/sec and the other symbols
maintain their original designations.
Problem solving:
p. 337: 42 - 44, 47 - 50.
Photoelectric effect: when light strikes the
surface of a metal, electrons are ejected.
(This is actually how photoelectric cells create
a current from cathode to anode.)
Problem with photoelectric effect: this effect
only occurs with light above a certain intensity.
How come energy from low levels of light
doesn't accumulate and eventually cause the
photoelectric effect?
Einstein explained it this way:
Photons carry energy packets called "quanta".
This energy is directly proportional to the
frequency of the light wave.
A photon therefore must be of sufficient
frequency and energy in order to liberate an
electron on the surface of a metal.
TO RECAP:
Energy is quantized into packets called
quanta.
Electromagnetic radiation (EM) has the
characteristics of both waves and
particulate matter. A quanta of EM is called
a photon.
So, here is where it gets a little deep…
We know that when white light is diffracted, it
separates into a continuous spectrum of colors
(ROYGBIV). However, then the light emitted
from an excited element is diffracted, we do
NOT get a continuous spectrum but instead get
a LINE spectrum, on a series of lines of
different colors.
WHAT DOES THIS MEAN?
It is further evidence that energy is quantized
and led to Bohr’s model of the cell.
QUANTUM NUMBERS in atomic theory are
based on this evidence.
Principal quantum numbers (n): integer values;
1, 2, 3, etc.
Angular momentum quantum numbers (l): has
values from 0 to n – 1 for each value of n.
Magnetic quantum numbers (m): includes all
integer values from l to –l including zero.