Download AP Notes Chapter 2

AP Notes Chapter 2
Atoms and Elements
History of the atom Summed-up
Greeks
Democritus
and Leucippus - atomos
Aristotle- elements.
Alchemy
1660 - Robert Boyle- experimental
definition of element.
Lavoisier- Father of modern chemistry.
Dalton’s Atomic Theory
1) Elements are made up of atoms
2) Atoms of each element are identical.
Atoms of different elements are
different.
3) Compounds are formed when atoms
combine. Each compound has a specific
number and kinds of atom.
4) Chemical reactions are rearrangement of
atoms. Atoms are not created or
destroyed.
The Atom

Dalton (early 1800s)
indivisible
A Helpful Observation
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Gay-Lussac- under the same conditions of
temperature and pressure, compounds
always react in whole number ratios by
volume.
Avagadro- interpreted that to mean
at the same temperature and pressure,
equal volumes of gas contain the same
number of particles.
(called Avagadro’s Hypothesis)
Experiments & theories to
determine what an atom was
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John Dalton- atoms indivisible
J. J. Thomson- Cathode ray tubes, electrons
Marie Curie- radioactivity
Robert Millikan- electron mass & charge
Ernest Rutherford- protons
James Chadwick- neutrons
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source
-
+
Thomson’s Experiment
Voltage source

+
Passing an electric current makes a beam
appear to move from the negative to the
positive end.
Thomson’s Experiment
Voltage source

By adding an electric field
Thomson’s Experiment
Voltage source
+
 By adding an electric field, he found that
the moving pieces were negative
The Atom

Thompson (~ 1900)
cloud of
(+) charge
. ..
.
.
.
... .
electron
(-) charge
“plum pudding” model
Thomsom’s Model
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Found the electron.
Couldn’t find positive
(for a while).
Said the atom was
like plum pudding.
A bunch of positive
stuff, with the
electrons able to be
removed.
Millikan’s Experiment
Atomizer
Oil droplets
+
-
Telescope
Oil
Millikan’s Experiment
X-rays
X-rays give some electrons a charge.
Millikan’s Experiment
•Some drops would hover
From the mass of the drop and the charge on
the plates, he calculated the mass of an electron
Radioactivity

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Discovered by accident
Henri Bequerel – photographic plates
Marie Curie – studied & named it
Three types
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
alpha- helium nucleus (+2 charge, large
mass)
beta- high speed electron
gamma- high energy light
James Chadwick
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Neutrons
Particles from radioactive polonium hit a
beryllium target and produced particle


no charge
slightly greater mass than the proton
Rutherford’s Experiment

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
Used uranium to produce alpha particles.
Aimed alpha particles at gold foil by
drilling hole in lead block.
Since the mass is evenly distributed in
gold atoms alpha particles should go
straight through.
Used gold foil because it could be made
atoms thin.
Rutherford’s Experiment
Lead
block
Uranium
Florescent
Screen
Gold Foil
Rutherford’s Experiment
What he expected
Rutherford’s Experiment
Because
Rutherford’s Experiment
Because, he thought the mass was
evenly distributed in the atom.
Rutherford’s Experiment
What he got
Rutherford’s Experiment
How he explained it

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Atom is mostly empty
Small dense,
positive piece
at center.
Alpha particles
are deflected by
it if they get close
enough.
+
Rutherford’s Experiment
+
Gold Foil Experiment

Rutherford (~1911) Nuclear Model
.. . . .
.
.
...
heavy central
(+) nucleus
e- “about”
nucleus
The Atom

Rutherford (~ 1911)
(e-) about
nucleus
.
. ..
.. .
heavy central
(+) nucleus
Nuclear Model
The Atom

Bohr (~ 1913)
central (+)
nucleus
n=3
n=2
n=1
.
....
.
. . . ..
.
e- in
allowed
orbits
Planetary Model
Modern View

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
The atom is mostly
empty space.
Two regions
Nucleus- protons
and neutrons.
Electron cloudregion where you
might find an
electron.
The Atom

Heisenberg, de Broglie, Schroedinger
(mid 1920s)
e- in regions
defined by math
functions
.
.. .. .
.. . . .
Quantum Mechanical Model
Sub-atomic Particles
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Z - atomic number = number of protons
determines type of atom.
A - mass number = number of protons +
neutrons.
Number of protons = number of electrons
if neutral.
Nuclear Symbols & Notation
Mass Number→
A
X
Z
23
24
Na
Na
11
11
←Element Symbol
Atomic Number→
Isotopes of elements
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Isotopes are forms of an atom that differ
by the number of neutrons
Mass number is approximation of exact
atomic mass of an isotope
Atomic mass or atomic weight is the
average mass of the isotopes of atoms
Isotopic percent abundance or fractional
abundance is a description of the
proportion of an isotope in a sample of an
element
Atomic Mass
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Atoms are so small, it is difficult to discuss
how much they weigh in grams.
Use atomic mass units.
an atomic mass unit (amu) is one twelth
the mass of a carbon-12 atom.
This gives us a basis for comparison.
The decimal numbers on the table are
atomic masses in amu.
They are not whole numbers



Because they are based on averages of
atoms and of isotopes.
can figure out the average atomic mass
from the mass of the isotopes and their
relative abundance.
add up the percent as decimals times the
masses of the isotopes.
Isotopes of Hydrogen
1
1
H hydrogen
2
1
H deuterium
3
1
H tritium
Examples


There are two isotopes of carbon 12C with
a mass of 12.00000 amu(98.892%), and
13C with a mass of 13.00335 amu
(1.108%).
There are two isotopes of nitrogen , one
with an atomic mass of 14.0031 amu and
one with a mass of 15.0001 amu. What is
the percent abundance of each?
Percent Abundance
Percent abundance = number of atoms of a given isotope
x 100%
total number of atoms of all isotopes
Fractional Abundance
Fractional abundance = Percent Abundance
100%
Atomic Weight =
(abundance isotope 1)(weight isotope1)
+ (abundance isotope 2)(weight isotope2)…
or
 %iso1 
 %iso 2 
AW  
(Wiso1)  
(Wiso 2)  ....
 100 
 100 
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A portion of an atom’s mass of protons,
neutrons and electrons is converted to
energy that holds the atom together.
Einstein gave us ΔE = (Δm)C2
The loss of this mass as the atom forms is
called the mass defect. This missing mass is
converted to “binding energy” (BE)
Mass atom = BE + #pro. + #elec. + #neu.
Allotrope
Different forms of the same
element that exist in the
same physical state under
the same conditions of
Temperature & Pressure
Carbon •Diamond
•Graphite
Graphite
Diamonds
Buckyballs
Periodic Table
Metals
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Conductors
Lose electrons
Malleable and ductile
Nonmetals
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Brittle
Gain electrons
Covalent bonds
Semi-metals or Metalloids
Alkali Metals
Alkaline Earth Metals
Halogens
Transition metals
Noble Gases
Inner Transition Metals
Periodic Table
1A
Families or Groups
2A
3A 4A 5A 6A 7A
3B 4B 5B 6B 7B
8B
1B 2B
8A
Periodic Table
Periods
1
2
3
4
5
6
7
8
Lanthanide Series
Actinide Series
Periods and Groups or Families
Hydrogen
The Hindenburg crash,
May 1939.
Shuttle main engines
use H2 and O2
Group 1A: Alkali Metals
Potassium
Reaction of
potassium + H2O
Cutting sodium metal
Group 2A: Alkaline Earth Metals
Magnesium
Magnesium Ablaze!
Magnesium
oxide
Calcium Carbonate—Limestone
The Appian Way, Italy
Champagne cave carved into
chalk in France
Group 3A: B, Al, Ga, In, Tl
Aluminum
Boron halides
BF3 & BI3
Gems & Minerals
Sapphire:
Al2O3 with
Fe3+ or Ti3+
impurity gives
blue whereas
V3+ gives
violet.
 Ruby: Al2O3
with Cr3+
impurity

Transition Elements
Lanthanides and
actinides
Iron in air gives
iron(III) oxide
Colors of Transition Metal Compounds
Iron
Cobalt
Nickel
Copper
Zinc
Group 4A: C, Si, Ge, Sn, Pb
Quartz, SiO2
Diamond
Group 5A: N, P, As, Sb, Bi
White and red
phosphorus
Phosphorus

Phosphorus first
isolated by Brandt
from urine, 1669
Group 6A: O, S, Se, Te, Po
Sulfuric acid
dripping from
snot-tite in cave
in Mexico
Sulfur from
a volcano
Group 7A:
F, Cl, Br, I, At
Halogen
Group 8A:
He, Ne, Ar, Kr, Xe, Rn

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Lighter than air balloons
“Neon” signs
XeOF4