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Chemistry
What is Chemistry?
The study of matter
and the changes
which it undergoes
• Metallurgy – Bronze Age, Iron Age
PRIMITIVE MAN DISCOVERS
• MELTING POINTS
• GLASS MAKING
• GLAZES
Egypt and Mesopotamia
- Discover chemical processes and
methods
- Metal workers hand down their methods
to their children, but don’t write much
down on paper (scrolls)
- Pass on knowledge to the Greeks
• Plato (400 BC) - four elements: earth,
water, fire and air
Fire
Earth
Air
Water
History of the atom
• Not the history of atom, but the idea of the
atom
• Original idea Ancient Greece (400 B.C..)
• Democritus and Leucippus Greek
philosophers
• Called minute particles “Seeds”
History of Atom
• Looked at beach Smallest possible
piece?
• Made of sand
• Cut sand - smaller Atomos - not to be
cut
sand
Another Greek
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•
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•
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Aristotle - Famous philosopher
All substances are made of 4 elements
Fire - Hot
Air - light
Earth - cool, heavy
Water - wet
Blend these in different proportions to
get all substances
Hellenistic Culture
• Not much experimentation, just
speculation
• ideas carried through middle ages.
• Alchemists change lead to gold
• Alchemy – Middle Ages
The Alchemist’s Dream
COPPER
“SILVER”
Zinc coated
“GOLD”
Brass = Copper + Zinc
Penny into Gold - Alchemist Dream
Timeline
Greeks
(Democratus ~450 BC)
Discontinuous
theory of matter
ALCHEMY
400 BC
300 AD
Issac Newton
(1642 - 1727)
1000
2000
Greeks
(Aristotle ~350 BC))
Continuous
theory of matter
American
Independence
(1776)
Alchemy
In Europe,
alchemy was
the quest for the Philosopher’s Stone.
Allegedly, this substance would turn
cheap metals into gold.
Transmutation
changing one substance into another

COPPER
Philosopher’s Stone

GOLD
Contributions
of alchemists:
Information about elements
- the elements mercury, sulfur, and antimony were discovered
- properties of some elements
Develop lab apparatus / procedures / experimental techniques
- alchemists learned how to prepare acids.
- developed several alloys
- new glassware
Modern Chemistry evolved
from Alchemy
• Antionne Lavoisier (1785)
- Chemistry as a
science began with
Lavoisier
- Relied on
quantitative,
reproducible
experiments
- Prepared a textbook
of Chemistry
Who’s Next?
• Late 1700’s - John Dalton- England
• Teacher- summarized results of his
experiments and those of other’s
• In Dalton’s Atomic Theory
• Combined ideas of elements with that
of atoms
• John Dalton (1808) – Atomic Theory
All matter consists of atoms are tiny indivisible particles of
an element that cannot be
created or destroyed.
Atoms of one element cannot
be converted into atoms of
another element.
Atoms of an element are
identical and are different from
atoms of any other element.
Dalton’s Atomic Theory
 All matter is made of tiny indivisible
particles called atoms.
 Atoms of the same element are identical,
those of different atoms are different.
 Atoms of different elements combine in
whole number ratios to form compounds
 Chemical reactions involve the
rearrangement of atoms. No new atoms
are created or destroyed.
Dmitri Mendeleev
(1834-1907)
In 1869, Mendeleev, a
Russian chemist, made a
list of all the chemical
elements that were
known at that time,
sorted according to
increasing atomic mass.
There were many gaps
in the table, and
according to them,
Mendeleev was able to
forecast that new
elements would be
found to fill the gaps.
Modern Periodic Table
Parts of Atoms
• J. J. Thomson - English physicist.
1897
• Made a piece of equipment called a
cathode ray tube or CRT.
• It is a vacuum tube - all the air has
been pumped out.
J. J. Thomson and his CRT
Thomson’s Experiment
Voltage source
-
+
Vacuum tube
Metal Disks
Thomson’s Experiment
Voltage source
-
+
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
 Passing
+
an electric current makes a
beam appear to move from the
negative to the positive end
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
 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
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
Thomson’s Experiment
Voltage source
+
 By
adding an electric field
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
Thomson’s Model
• 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
Rutherford’s experiment
• Ernest Rutherford English physicist.
(1910)
• Believed in the plum pudding model of
the atom.
• Wanted to see how big they are
• Used radioactivity
• Alpha particles - positively charged
pieces given off by uranium
• Shot them at gold foil which can be
made a few atoms thick
Rutherford’s experiment
• When the alpha particles hit a
florescent screen, it glows.
• Here’s what it looked like (pg 72)
Lead
block
Uranium
Florescent
Screen
Gold Foil
He Expected
• The alpha particles to pass through
without changing direction very much
• Because
• The positive charges were spread out
evenly. Alone they were not enough to
stop the alpha particles
What he expected
Because
Because, he thought the mass was
evenly distributed in the atom
Because, he thought
the mass was evenly
distributed in the atom
What he got
How he explained it
• Atom is mostly empty
• Small dense,
positive piece
at center
• Alpha particles
are deflected by
it if they get close
enough
+
Movie
+
Density and the Atom
• Since most of the particles went
through, it was mostly empty.
• Because the pieces turned so much, the
positive pieces were heavy.
• Small volume, big mass, big density
• This small dense positive area is the
nucleus
Modern View of the Atom
• The atom is
mostly empty
space
• Two regions
• Nucleus- protons
and neutrons
• Electron cloudregion where you
might find an
electron
Structure of the Atom
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•
•
•
•
•
There are two regions
The nucleus
With protons and neutrons
Positive charge
Almost all the mass
Electron cloud- Most of the volume of
an atom
• The region where the electron can be
found
Size of an Atom
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Atoms are small.
Measured in picometers, 10-12 meters
Hydrogen atom, 32 pm radius
Nucleus tiny compared to atom
If the atom was the size of a stadium, the
nucleus would be the size of a marble.
• Radius of the nucleus near 10-15m.
• Density near 1014 g/cc
Subatomic Particles
Relative Actual
mass (g)
Name Symbol Charge mass
Electron
e-
-1
1/1840 9.11 x 10-28
Proton
p+
+1
1
1.67 x 10-24
Neutron
n0
0
1
1.67 x 10-24
Counting the Pieces
• Atomic Number = number of protons
• # of protons determines kind of atom
• The same as the number of electrons in
the neutral atom
• Mass Number = the number of protons
+ neutrons
• All the things with mass
Symbols
• Contain the symbol of the element, the
mass number and the atomic number
Symbols
• Contain the symbol of the element, the
mass number and the atomic number
Mass
number
Atomic
number
X
Symbols
• Find the
– number of protons
– number of neutrons
– number of electrons
– Atomic number
– Mass Number
19
9
F
Symbols
 Find
the
–number of protons
–number of neutrons
–number of electrons
–Atomic number
–Mass Number
80
35
Br
Symbols
 If
an element has an atomic
number of 34 and a mass number
of 78 what is the
–number of protons
–number of neutrons
–number of electrons
–Complete symbol
Symbols
 If
an element has 91 protons and
140 neutrons what is the
–Atomic number
–Mass number
–number of electrons
–Complete symbol
Symbols
 If
an element has 78 electrons and
117 neutrons what is the
–Atomic number
–Mass number
–number of protons
–Complete symbol
Isotopes
• Dalton was wrong.
• Atoms of the same element can have
different numbers of neutrons
• Different mass numbers
• Called isotopes
Naming Isotopes
• Put the mass number after the name of
the element
• carbon- 12
• carbon -14
• uranium-235
Atomic Mass
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•
•
•
How heavy is an atom of oxygen?
There are different kinds of oxygen atoms.
More concerned with average atomic mass.
Based on abundance of each element in
nature.
• Don’t use grams because the numbers
would be too small
Measuring Atomic Mass
• Unit is the Atomic Mass Unit (amu)
• One twelfth the mass of a carbon-12
atom.
• Each isotope has its own atomic mass
we need the average from percent
abundance.
Calculating averages
• You have five rocks, four with a mass of 50
g, and one with a mass of 60 g. What is
the average mass of the rocks?
• Total mass =
4 x 50 + 1 x 60 = 260 g
• Average mass = 4 x 50 + 1 x 60 = 260 g
5
5
• Average mass = 4 x 50 + 1 x 60 = 260 g
5
5
5
Calculating averages
• Average mass = 4 x 50 + 1 x 60 = 260 g
5
5
5
• Average mass = .8 x 50 + .2 x 60
• 80% of the rocks were 50 grams
• 20% of the rocks were 60 grams
• Average = % as decimal x mass +
% as decimal x mass +
% as decimal x mass +
Atomic Mass
• Calculate the atomic mass of copper if
copper has two isotopes. 69.1% has a mass
of 62.93 amu and the rest has a mass of
64.93 amu.
Atomic Mass
• Magnesium has three isotopes. 78.99%
magnesium 24 with a mass of 23.9850
amu, 10.00% magnesium 25 with a mass
of 24.9858 amu, and the rest magnesium
25 with a mass of 25.9826 amu. What is
the atomic mass of magnesium?
• If not told otherwise, the mass of the
isotope is the mass number in amu
Atomic Mass
• Is not a whole number because it is an
average.
• Are the decimal numbers on the
periodic table.
The Periodic Table
States
• Different states of a substance are different
physical ways of packing its component particles.
Some elements and all
compounds consist of
molecules or crystal
lattices, which in turn
consist of atoms or ions
joined by chemical
bonds.
2 or more elements
combined
in a unique ratio
•Are basic forms of
MATTER
IRON
CALCIUM
SULFUR
SODIUM
•Cannot be broken
down into simpler
substances by
chemical reactions
Lustre
conduct electricity
ductile
malleable
high melting points
and densities
Na sodium
Solids at room
temperature except
mercury Hg
K potassium
Mg magnesium
Cu copper
Ag Silver
Fe iron
•Not very shiny
•poor conductors of
heat and electricity
•not ductile
•not malleable
•lower melting
points and densities
•C -carbon
•O -oxygen
•S -sulfur
•H -hydrogen
•N -nitrogen
colour
odour
taste
density
hardness
solubility
melting point
boiling point
Each chemical
substance has a
unique set of
properties that
distinguishes it
from every other
substance
Chemical Symbols
of the Elements
C carbon
Ca calcium
P phosphorus
Fe iron -ferrum
Pb lead - plumbum
Allotropes
• Allotropes: Some elements occur in different
forms due to the different chemical arrangement
of their constituent atoms. Eg. Carbon:
diamond
graphite
soot
Buckminsterfullerene
Allotropes
• Allotropes: Some elements occur in different
forms due to the different chemical arrangement
of their constituent atoms. Eg. Carbon:
diamond
graphite
soot
(tiny
graphite particles)
Buckminsterfullerene
Allotropes
• Allotropes: Some elements occur in different
forms due to the different chemical arrangement
of their constituent atoms. Eg. Carbon:
diamond
graphite
soot
(tiny
graphite particles)
Buckminsterfullerene
Usually one form is more stable at a given temperature
and pressure.
Consist of 2 or more elements joined together in
fixed proportions to form new substances
NaCl salt sodium chloride
H20 water
Atoms are joined together by chemical bonds.
Formed by chemical reactions
Can be broken down into their constituent
elements by chemical reactions
A compound has its own physical and chemical
properties that are quite distinct from those of the
elements themselves.
Compounds
Eg. Salt – a compound of sodium and chlorine
+
Sodium
• Soft metal
• Reacts
violently
with water
Chlorine
• Yellow gas
• Molecules
• Very
poisonous
Salt
• Clear crystals
• Hard but brittle
• Used to flavour
food
Structures consisting of two or more atoms
that are chemically bound together and
behave as an independent unit.
The atoms can be from the same element
(eg. N2) or different elements (eg. H2O).
Nitrogen, N2
Water, H2O
Methane, CH4
Ammonia, NH3
Alcohol, CH3CH2OH
Contain more than one substance
elements and/or compounds
They have a variable composition -are not
pure
A homogeneous mixture is a SOLUTION
AIR - contains
•elements nitrogen-N oxygen O
•contains compounds carbon dioxide, water
• An atom is a chemically indivisible particle
of an element. Cannot be chemically
created, destroyed or changed. (eg. H, O,
C)
• A molecule consists of two or more atoms
chemically bonded together. The atoms
can be from the same or different
elements. (eg. H2O, C2H5OH)
• An element contains atoms of only one type.
Cannot be chemically decomposed. (eg.
hydrogen, oxygen, carbon)
• A compound is composed of more than one type
of atom joined by chemical bonds. It always has
the same elements combined in the same
integer ratio. Its properties are different to those
of the component elements. (eg. water, alcohol)
• A mixture has different elements or compounds
mingled together. The properties of the
components are maintained. (eg. beer, martini)
Definitions
• Different allotropes of element are
different chemical ways of bonding its
component atoms. (eg. diamond vs
graphite vs soot for carbon)
• Different states of a substance are
different physical ways of packing its
component particles. (eg. water vs ice)