Download 17-Sept

Chemistry 6A Fall 2007
Chem. 6A This week:
Dr. J. A. Mack
CSUS Chem 6A F07 Dr. Mack
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It’s time to play…
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Experiment
Lecture:
Chapter 2
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(You will need goggles!!)
No goggles, no lab!
No open toed shoes allowed!
No pre-lab, no lab!
No excuses!
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9-17-07
Lab:
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It’s time to play…
Cs
cesium
MgCl2
magnesium chloride
Hg
Mercury
CuSO4
copper (II) sulfate
Zn
zinc
calcium acetate
Ca(C2H3O2)2
As
Arsenic
hydrogen hydroxide
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HOH
or water… H2O
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The modern periodic table is defined by:
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Groups (families)
(columns down)
The Periods are labeled:
2
3
Periods (rows across)
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The Groups are labeled:
1A
7A 8A
2A
3A 4A 5A 6A
3B 4B 5B 6B 7B
The “A” refers to
the “main group
elements”
8B
1B 2B
The “B” refers to the
transition metal elements.
Tin is in group 4A (14) in the 5th period.
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Periodic Table: Metallic
Periodic Table: Metallic
arrangement
arrangement
1
IA
1
18
VIIIA
2
IIA
13
IIIA
14
IVA
15
VA
16
VIA
17
VIIA
1
IA
1
2
18
VIIIA
2
IIA
13
IIIA
14
IVA
15
VA
16
VIA
17
VIIA
2
3
IIIB
3
4
4
IVB
5
VB
6
VIB
7
VIIB
8
9
VIIIB
10
11
IB
12
IIB
Nonmetals
Metals
5
6
7
7
12
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Today’s Periodic table
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VIB
7
VIIB
8
9
VIIIB
10
11
IB
12
IIB
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Metalloids
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Today’s Periodic table
Group 1A elements are also
know as the “Alkali Metals” as
they form basic salts
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VB
somewhere in
between metals
and non-metals
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IVB
4
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3
IIIB
3
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Group 2A elements are also
know as the “Alkaline earth
Metals” as they are only found
in the ground as metal salts
(carbonates)
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Today’s Periodic table
Today’s Periodic table
Group 2B – 8B elements are also know as
the “Transition Metals”.
Metals” They may be
found in the earth as pure metals or as ores
(salts).
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Group 7A elements are also
know as the “Halogens”. They
form acids with hydrogen and
exist as diatomic molecules.
(F2, Cl2…)
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Today’s Periodic table
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The discovery of modern atomic structure:
Group 8A elements are also
know as the “Noble gasses”.
They are inert to reaction for
the most part. He is found
underground!
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Experiments!
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Rutherford’s Scattering Experiment: 1911
Rutherford’s Experiment: Explained
•Most of the α-particles passed
through the gold foil.
•Some α-particles were deflected
slightly as they came close to the
nucleus by the + charge repulsion.
•Some were deflect backwards by
direct collisions with the nucleus.
Conclusion:
•Atoms are mostly space.
•The nucleus caries most of the
mass with a positive charge.
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The Composition of an Atom:
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Further experiments lead to the discovery and characterization of
the electron, proton and neutron.
Electron:
-1 charge
The atom is mostly
empty space
J.J. Thompson cathode ray tube (1897)
electrons were negatively charged
R. Millkan Oil drop experiment (1909)
charge on the electron
Proton:
+1 charge
•protons and neutrons in the nucleus.
•the number of electrons is equal to the
number of protons.
Neutron:
no charge
E. Rutherford (1918)
hydrogen nucleus termed a “proton”
J. Chadwick (1932)
neutral particle with the mass of a proton
•electrons in space around the nucleus.
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Atomic Number, Z
Isotopes, Atomic Numbers, and Mass Numbers
•Atomic number (Z) = number of protons in the nucleus.
An element’s identity is defined by
the number of protons in the
nucleus: Z
•Mass number (A) = total number of nucleons in the
nucleus (i.e., protons and neutrons).
•One nucleon has a mass of 1 amu
(Atomic
Atomic Mass Unit)
Dalton”
Unit a.k.a “Dalton
Atomic number
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•Isotopes have the same Z but different A.
Atom symbol
Al
•The elements are arranged by Z on the periodic table.
Atomic weight
26.981
By convention, for element X, we write
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75
The isotope 34
Se is used medically for diagnosis of
75
34 Se
have?
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These isotopes occur in proportions represented by their
natural abundances.
75
34 Se
As macroscopic beings, we measure matter on a “bulk”
scale (many atoms).
34 protons
electrons = 34
The fraction or abundance of each of the individual
isotopes statistically weights the average atomic mass of
an element.
neutrons = 75-34 = 41
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In nature, an element is found to contain a mixture of all
of the naturally occurring isotopes.
75 protons +
neutrons
protons = 34
X
Atomic Masses and the Periodic Table:
pancreatic disorders. How many protons, neutrons, and
electrons does an atom of
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A
Z
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Example:
most
The sum of the
intensities adds up
to 100%.
Chlorine has two isotopes:
The relative
Cl-35
abundance of each
35
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isotope is indicated
by the height of the
least
line corresponding
&
Cl- 37
37
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Cl
shorthand notation
Cl
Each isotope occurs in nature with a specific mass and
corresponding fraction or “Percent Abundance”.
35
17
to a particular mass.
75.53 %
37
17
Cl
34.96885 u
24.47 %
Cl
36.96590 u
1 u = 1 amu
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fraction
that are
Cl-35
mass of a
Cl-35
atom
m Cl (u) = m Cl-35 ×
abundance
of Cl-35
mass of a
Cl-37
atom
+ m Cl-37 ×
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Avogadro’s Number and the Mole
The average weighted atomic mass is determined by the
following mathematical expression:
Average
mass of a
Cl atom
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The concept of a mole is defined so that we
may equate the amount of matter (mass) to
the number of particles (mole).
fraction
that are
Cl-37
The Standard is based upon the C-12
isotope.
abundance
of Cl-37
The atomic mass of 12C is defined as exactly 12 u.
= 34.96885u × 0.7553 + 36.96590 × 0.2447 = 35.45 u
The atomic mass of 12C is 1.99265 × 10-23 g.
(4 sig. fig)
1 amu = (the mass of one 12C atom ÷12) = 1.66054 × 10-24g
= 1.66054 × 10-27 kg
This is the value that is reported on the periodic table.
Note that: 0.7553 + 0.2447 = 1.0000 (100%)
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Molar Masses
Avagagro’s Number
Since we can equate mass (how much matter) with moles
12C
Since one mole of
has a mass of 12g (exactly), 12g of
contains 6.022142 x 1023 12C-atoms.
(how many particles) we now have a conversion
that relates the two.
12C
But carbon exists as 3 isotopes: C-12, C-13 &C-14
mols
The average atomic mass of carbon is 12.011 u.
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aka: Avogadro's number (NA)
Yes, since NA is so large,
the statistics hold.
CSUS Chem 6A F07 Dr. Mack
molar mass (g/mol) = grams
The Molar Mass of a substance is the amount of matter that
contains one-mole or 6.022 × 1023 particles.
From this we conclude that 12.011g of carbon contains
6.022142 x 1023 C-atoms
Is this a valid
assumption?
×
factor
The atomic masses on the Periodic Table also represent the
molar masses of each element in grams per mole (g/mol)
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So if you have 12.011g of carbon…
you have 6.022×1023 carbon atoms!
So if you have 39.95g of argon…
you have 6.022×1023 argon atoms!
if you have a mole of dollar bills… you are Bill Gates…
you have 6.022×1023 bucks!
and if you have 6.022×1023 avocados…
you have…
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a “guacamole”
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