Download - Thermodynamics Study of heat flow
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Lecture 3
Professor Hicks
Inorganic Chemistry (CHE151)
Coulomb’s Law
• Some types of matter can acquire a
property called charge when rubbed
together
• There are two types
positive (+) negative (-)
+ -
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Coulomb’s Law
• Opposite charges are attracted
• Like charges are repelled
+ -
+
+ -
-
Discovery of the electron
• Electrons can be made to flow out of all kinds of matter
• They are therefore building blocks of all matter
• They are negatively charged and matter is not charged
there must be a positive part also
• Bending of the rays charge to mass ratio of the electron
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Millikan oil-drop experiment
Rutherford’s Gold Foil Experiment • particles are positive particles emitted from radioactive substances
• They are also seen flowing towards the negative plate when helium is
placed in the cathode ray tube before evacuating
• Most of the particles go straight through!
The atom must have lots of empty space
Those that are deflected must have hit something so most of the matter of
the atom is compacted into small regions we call the nucleus
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Subatomic particles
• All matter contains:
negative particles called electrons
positive particles called protons
uncharged particles called neutrons
• Protons and neutrons approximately same
mass (~1.0 amu)
• Electrons mass 1/1836 amu
• Proton and electron have the same exact
charge (1.6 x 10-19 C)
Organization of the atom
• Typical size 10-10 m
• Most of volume
occupied by electrons
• Electrically neutral
#protons = # electrons
electrons
nucleus
10-15 m
10-10 m + charge = - charge
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Each element has a different
number of protons
# protons
• Same # protons
different # neutron
• Isotopes are versions of an
element with different # neutrons
Isotopes
boron-10
+ +
+
+
+
N
N
N
N
N
boron-11
+ +
+
+
+
N
N
N
N
N
N Both are boron (5 protons)
different # neutrons
different isotopes of boron
= an isotope
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More on isotopes
Two isotopes of boron
Boron-10
+ +
+
+
+
N
N
N
N
N
Boron-11
+ +
+
+
+
N
N
N
N
N
N
• Elements in nature are mixtures
of different isotopes
• Each Isotope has a different mass
• Nuclei of some isotopes are unstable
- break down in nuclear reactions
Isotope notation
C 13
6 element symbol
nuclear charge (Z)
# protons
mass number (A)
= # protons
+ # neutrons
pronounced “carbon 13”
How many neutrons?
mass number - # protons= # neutrons
= A-Z
=13 – 6 = 7 neutrons
can also be written “carbon-13”
or “C-13”
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Discuss discovery of the
proton and the neutron
Weighted averages
• A way to calculate different weight for different
types of contribution
Example: Grade is calculated as weighted averages
grade = 15% Quizzes + 60% Exams + 25% Lab
To write it as a math equation convert % /100
grade = 15 x Quizzes + 60 x Exams + 25 x Lab
100 100 100
percentages are the weights
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Weighted averages
How does it compare to a regular average?
Grade = 15 x Quizzes + 60 x Exams + 25 x Lab
100 100 100
grade = Quizzes + Exams + Lab
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grade = 33 x Quizzes + 33 x Exams + 33 x Lab
100 100 100
which you can rewrite as
regular average = all same weight
Atomic mass and periodic table
The atomic mass is
weighted average
of isotope masses
# protons
natural Sn is a mixture of:
Sn 120
50
Sn 116
50
Sn 118
50
Sn 122
50
Sn 119
50 Sn 117
50
Sn 115
50 Sn 114
50
Sn 124
50
Sn 115
50 Sn 114
50 Sn 112
50
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Example. Carbon found in nature is mostly two
isotopes, carbon-12, and carbon-13. They have
abundances of 98.9% and 1.1%. What is the
atomic mass of natural carbon in amu?
atomic mass = 98.9 x 12.00 amu
100
+ 1.1 x 13.00 amu
100
carbon-12 has mass of 12.00 amu
carbon-13 has mass of 13.00 amu
12.01 amu
C 12
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C 13
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Mass spectrometer
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Describe & Discuss
Mass Spectrometer
at the board
Another Example of a Weighted Average
Average Density
• If an object is made up of more than oe type of
matter its density is a weighted average of the
densities of the various components
• If the volumes did not change (as they
sometimes do when homogenous mixtures are
formed)
Average Density = Volume component 1 × Density of component 1
Total volume
+ Volume component 2 × Density of component 2
Total volume
+ …etc.
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Chlorine consists of two isotopes Cl-35
and Cl-37. Calculate the natural
abundances of each.
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Ions
• Atoms are electrically neutral
positive charge = negative charge
#protons = # electrons
• Atoms can gain or lose electrons to form
Monatomic ions
• Gaining electrons forms anions (negative ions )
• Losing electrons forms cations (positive ions)
I- K+
lost 2
electrons
Ca2+
N3-
gained 3
electrons
Notating charges
Na+
lost 1
electron K+
lost 1
electron
Al3+
lost 3
electrons
F-
gained 1
electron
gained 2
electrons
O2-
Charge written as number of electrons lost (+) or
gained (-) in superscript
Examples
Na+ K+ Ca2+ Al3+ F- O2- N3-
Ions are visualized
as spheres
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Trend in type I (fixed-charge) ions
• Same columns (groups) = same charge
• Metals form positive ions
• Non-metals form negative ions
metals
non-metals
metals in this area can have
more than one ion
called variable charge ions
+1
+2 +3 -3
-1 -2
memorize these trends
also a few of these
metals can also form
variable charge ions
Ionic compounds
• Electrically neutral
• Charge positive ions = charge negative ions
NaCl = 1 Na+ and 1 Cl-
Li2S = 2 Li+ and 1 S2-
CaF2 = 1 Ca2+ and 2 F-
-1 +1
-2 +1 +1
2+ -1 -1
Only one compound for
each combination of ions
Na2Cl NaCl2
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Molecular compounds are more
numerous than ionic compounds • Binary compounds are one with only two
elements
• Knowing what elements are in a binary molecular compound is not enough to determine its chemical formula
N2O4
NO Viagra
activates NO
Rocket fuel
NO2 Smog
N2O
Laughing gas
aka whippets, hippie crack
Formula Unit • Chemical formula of ionic compound called Formula Unit
• Smallest whole number ratio of ions that will be electrically neutral
SrO = 1 Sr2+ and 1 O2-
168 Na+ and 168 Cl-
1019 Na+ and 1019 Cl-
1022 Na+ and 1022 Cl-
CaCl2 = 1 Ca2+ and 2 Cl- Li2O = 2 Li+ and 1 O2-
NaCl = 1 Na+ and 1 Cl-
Na168Cl168
Na Cl 1019 1019
Na Cl 1022 1022
smallest whole number ratio is same for different size lattices
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Crossing over rule (How to figure out the formula unit of an ionic compound)
Ca Ca2+ N3- N
3-
2+
2+
2+
3-
total +
charge
3 x 2
total -
charge
2 x 3
=
3 2
=
3 2 =
periodic
table
periodic
table
What is the formula unit of the ionic compound
made from calcium and nitrogen?
Why? b/c ionic compounds
electrically neutral
Ca3N2
Crossing over rule
Mg Mg2+ O2- O
2 2
periodic
table
periodic
table
What is the formula unit of the ionic compound
made from magnesium and oxygen?
Why not
Mg2O2?
b/c the formula unit has smallest whole number ratio
of ions that will be electrically neutral (1 to 1 smaller 2 to 2)
MgO
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Polyatomic ions
• Groups of atoms bonded
together that have a charge
Hg2 2+
PO43- NH4
+ CN-
OH-
SO42-
• Acts as a single ion
H C O O O
atoms
+ e-
H
C O O
O
-1
HCO3-
HCO3-
Polyatomic ions form ionic
compounds
Hg2 2+ PO4
3-
NH4+
CN-
OH-
SO42- HCO3
-
• Positive polyatomic ions can substitute a metal ion
• Negative polyatomic ions can substitute a non-metal ion
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( ) 2
Crossing over rule (polyatomic ions)
Ca Ca2+ PO43- phosphate
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periodic
table
table of
ions
What is the formula unit of the ionic compound
made from calcium and phosphate ions?
why use
( ) ? Ca3(PO4)2
(a polyatomic ion)
PO43- PO4
3- Ca2+ Ca2+ Ca2+
2 PO43- ions
not PO423-
Counting atoms in chemical formula
Ca3(PO4)2
PO43- PO4
3- Ca2+ Ca2+ Ca2+
# Ca 2+ ions = 3
# PO43- ions = 2
1 P + 4 O 1 P + 4 O
total = 2 P and 8 O
3 Ca
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Write formulas for the ionic compounds
formed from:
a) Li+ and O2-
b) Li+ and O22-
c) Hg2+ and F-
d) Hg22+ and F-
e) Hg22+ and O2-
f) Hg22+ and O2
2-
g) Al3+ and C4-
h) Ca2+ and C4-
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Main Group Elements
Transition Metals
Lanthanides/Actinides
Naming monatomic ions
• Main group negative ions add –ide
Cl- = chloride ion
O2- = oxide ion
• Main group positive ions
“metal name” ion
• Na+ = sodium ion
• Al3+ = aluminum ion
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Naming Type II (variable charge) ions
Fe2+ = Iron (II) ion
Fe3+ = Iron (III) ion
Ag+ = Silver (I) ion
metals
non-metals
most transition metals
can form type II ions
metal name roman numeral of charge ion
example
a few of these
metals also
form type II ions
Naming ionic compounds
(with fixed charge ions)
metal name anion name
sodium bromide
lithium sulfide
NaBr
Li2S
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Naming ionic compounds
• metal name anion name
for polyatomic ions
substitute either part
with name Table 8.4
sodium dihydrogen phosphate
lithium dichromate
NaH2PO4
Li2Cr2O7
ammonium sulfate
(NH4)2 SO4
(with polyatomic ions)
Naming ionic compounds
• metal name anion name
metal ions that can have different
charges use roman numerals
Iron (III) chloride
Copper (II) dichromate
FeCl3
CuCr2O7
(with variable charge ions)
(Fe3+ and 3Cl-)
(Cu2+ and Cr2O72-)
you will have this
chart on the exam
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Naming ionic compounds with
waters of hydration
• The waters of hydration
are shown after the dot
• Add a prefix for the
number with hydrate
heat
CuSO4 5H2O CuSO4 + 5H2O Copper (II) sulfate pentahydrate
hydrated form anhydrous form
Prefixes
mono, di, tri, tetra,
penta, hexa, hepta,
octa, nona, deca
Naming binary molecular compounds
• Element further to left on PT first
• If in same group lower element comes first
• Both elements get prefixes (mono, di, tri, tetra, penta, hexa, hepta, octa, nona; mono optional)
• Second element gets ending -ide
N2O4
NO nitrogen oxide
dinitrogen tetroxide
NO2 nitrogen dioxide
N2O
dinitrogen oxide
(2 elements)
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Molecular vs ionic compounds
• Chemical formula of an ionic compound is called its formula unit
• It has smallest whole number ratio of ions
• Formula unit predicted from crossing over rule
making only one formula possible
no prefixes needed (except for waters of hydration)
• In contrast different molecular compounds with same elements are numerous, NO, NO2, N2O, N2O4 etc.
prefixes required to describe each compound
The chemical formulas of molecular compounds
predicted by Lewis Structures ( chapter 10)
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