Chemistry

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Chemistry
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What is Chemistry?

• The study of matter and the changes which it
  undergoes

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History of Chemistry

• Metallurgy Bronze Age, Iron Age

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PRIMITIVE MAN DISCOVERS

• MELTING POINTS
• GLASS MAKING
• GLAZES

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Egypt and Mesopotamia

• Discover chemical processes and methods
• Metal workers hand down their methods to their
  children, but dont write much down on paper
  (scrolls)
• Pass on knowledge to the Greeks

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History of Chemistry

• Plato (400 BC) - four elements earth,
  water, fire and air

Fire
Air
Earth
Water
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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

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History of Atom

• Looked at beach
• Made of sand
• Cut sand - smaller sand

• Smallest possible piece?
• Atomos - not to be cut

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Another Greek

• 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

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Hellenistic Culture

• Not much experimentation, just speculation
• ideas carried through middle ages.
• Alchemists change lead to gold

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History of Chemistry

• Alchemy Middle Ages

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The Alchemists Dream
COPPER SILVER GOLD
Zinc coated Brass Copper Zinc
Penny into Gold - Alchemist Dream
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Timeline
Greeks (Democratus 450 BC) Discontinuous
theory of matter
Issac Newton (1642 - 1727)
2000
1000
300 AD
400 BC
Greeks (Aristotle 350 BC)) Continuous theory
of matter
American Independence (1776)
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Alchemy
In Europe, alchemy was
the quest for the Philosophers Stone.

• Allegedly, this substance would turn
• cheap metals into gold.

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• Transmutation

changing one substance into another
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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
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Modern Chemistry evolved from Alchemy
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History of Chemistry

• Antionne Lavoisier (1785)

• - Chemistry as a science began with Lavoisier
• Relied on quantitative, reproducible experiments
• - Prepared a textbook of Chemistry

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Whos Next?

• Late 1700s - John Dalton- England
• Teacher- summarized results of his experiments
  and those of others
• In Daltons Atomic Theory
• Combined ideas of elements with that of atoms

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History of Chemistry

• 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.
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Daltons 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.

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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.
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Modern Periodic Table
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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.

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J. J. Thomson and his CRT
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Thomsons Experiment

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Vacuum tube
Metal Disks
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Thomsons Experiment

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Thomsons Experiment

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Thomsons Experiment

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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Thomsons Experiment

• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field

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Thomsons Experiment

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• By adding an electric field he found that the
  moving pieces were negative

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Thomsons Model

• Found the electron
• Couldnt find positive (for a while)
• Said the atom was like plum pudding
• A bunch of positive stuff, with the electrons
  able to be removed

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Rutherfords 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

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Rutherfords experiment

• When the alpha particles hit a florescent screen,
  it glows.
• Heres what it looked like (pg 72)

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Florescent Screen
Lead block
Uranium
Gold Foil
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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

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What he expected
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Because
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Because, he thought the mass was evenly
distributed in the atom
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Because, he thought the mass was evenly
distributed in the atom
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What he got
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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

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Movie
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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

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Modern View of the Atom

• The atom is mostly empty space
• Two regions
• Nucleus- protons and neutrons
• Electron cloud- region where you might find an
  electron

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Structure of the Atom

• 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

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Size of an Atom

• 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

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Subatomic Particles
Actual mass (g)
Relative mass
Name
Symbol
Charge
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
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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

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Symbols

• Contain the symbol of the element, the mass
  number and the atomic number

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Symbols

• Contain the symbol of the element, the mass
  number and the atomic number

Mass number
X
Atomic number
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Symbols

• Find the
• number of protons
• number of neutrons
• number of electrons
• Atomic number
• Mass Number

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F
9
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Symbols

• Find the
• number of protons
• number of neutrons
• number of electrons
• Atomic number
• Mass Number

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Br
35
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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

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Symbols

• If an element has 91 protons and 140 neutrons
  what is the
• Atomic number
• Mass number
• number of electrons
• Complete symbol

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Symbols

• If an element has 78 electrons and 117 neutrons
  what is the
• Atomic number
• Mass number
• number of protons
• Complete symbol

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Isotopes

• Dalton was wrong.
• Atoms of the same element can have different
  numbers of neutrons
• Different mass numbers
• Called isotopes

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Naming Isotopes

• Put the mass number after the name of the element
• carbon- 12
• carbon -14
• uranium-235

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Atomic Mass

• 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.
• Dont use grams because the numbers would be too
  small

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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.

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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

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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

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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.

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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

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Atomic Mass

• Is not a whole number because it is an average.
• Are the decimal numbers on the periodic table.

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The Periodic Table
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States of Matter
Solid
Gas
Liquid
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States

• Different states of a substance are different
  physical ways of packing its component particles.

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Pure Substance
Compound
Element
2 or more elements combined in a unique ratio
Some elements and all compounds consist of
molecules or crystal lattices, which in turn
consist of atoms or ions joined by chemical bonds.
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Elements

• Are basic forms of MATTER
• Cannot be broken down into simpler substances by
  chemical reactions

IRON CALCIUM SULFUR SODIUM
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Lustre conduct electricity ductile malleable high
melting points and densities
METALS
Na sodium K potassium Mg magnesium Cu copper Ag
Silver Fe iron
Solids at room temperature except mercury Hg
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• 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

Non-Metals
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Physical Properties of Elements
colour odour taste density hardness solubility mel
ting point boiling point
Each chemical substance has a unique set of
properties that distinguishes it from every other
substance
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Chemical Symbols of the Elements
C carbon Ca calcium P phosphorus Fe
iron -ferrum Pb lead - plumbum
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Allotropes

• Allotropes Some elements occur in different
  forms due to the different chemical arrangement
  of their constituent atoms. Eg. Carbon
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soot
diamond
graphite
Buckminster- fullerene
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Allotropes

• Allotropes Some elements occur in different
  forms due to the different chemical arrangement
  of their constituent atoms. Eg. Carbon
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soot (tiny graphite particles)
diamond
graphite
Buckminster- fullerene
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Allotropes

• Allotropes Some elements occur in different
  forms due to the different chemical arrangement
  of their constituent atoms. Eg. Carbon
•   Usually one form is more stable at a given
  temperature and pressure.

soot (tiny graphite particles)
diamond
graphite
Buckminster- fullerene
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Compounds
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.
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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

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Molecules

• 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).

Water, H2O
Nitrogen, N2
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Molecules
Ammonia, NH3
Methane, CH4
Alcohol, CH3CH2OH
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Mixtures

• 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

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Types of Particles

• An atom is a chemically indivisible particle of
  an element. Cannot be chemically created,
  destroyed or changed. (eg. H, O, C)
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• A molecule consists of two or more atoms
  chemically bonded together. The atoms can be from
  the same or different elements. (eg. H2O, C2H5OH)

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Types of Substances

• An element contains atoms of only one type.
  Cannot be chemically decomposed. (eg. hydrogen,
  oxygen, carbon)
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• 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)

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Definitions
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Types of Substances

• 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)