Chemistry and Society

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Chemistry and Society

• Chapter 2 Connections

Dr. Victor Vilchiz VSU Fall 2005
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Alchemy

• Is in essence the ancestor of modern chemistry
• Alchemy was more than a science
• It was a philosophy
• A way of life
• Alchemists strived to reach pureness and
  perfection.
• Alchemists venerated gold as the symbol of
  perfection

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Alchemy

• It was believed that to posses gold will make you
  rich and pure
• To drink gold meant to live forever
• Alchemy became the movement to find a way to
  transform (transmute) matter into gold.
• While these believes may seem silly and/or
  far-fetched they were widely accepted.

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The search for the elixir of life

• It was known that it was possible to take iron
  and make steel and that if you mixed copper and
  zinc you will get brass.
• Why wouldnt be possible to make gold?
• Needless to say the search for the elixir was
  futile and eventually alchemy gave way to new
  scientific questions and approaches.

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Alchemys Legacy

• While it might be true that alchemy failed to
  produce an answer to its driving force it was not
  by any means a waste.
• Many process we now use were discovered or
  developed during the alchemists years.
• Distillation
• Fermentation
• Putrefaction
• Many elements were also discovered
• Bi, Zn, As, Co, and P

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Alchemy to Chemistry

• Where does Chemistry come from?
• We are not 100 sure where the name comes from
  but there are several possibilities
• It could had come from Egypt? Khem turn black
• It could had come from Greece?Cheoto cast
• It could had come from China?Chin-Igold making
  juice.

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Where to now?

• So making gold was not possible now what?
• The obvious question will be then why cant we
  make gold?
• The quest to understand what was going on began
  and thus modern chemistry was born.

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Ancient to Modern

• In the ancient times of alchemy we had only
  AFEW Elements.
• Air
• Fire
• Earth
• Water
• Currently we know 116 elements of which only 111
  are recognized by the IUPAC.

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The study of AIR

• Gold was replaced by air as the primary study
  subject.
• It is abundant and it behaves differently under
  different circumstances.
• It was pointed out that at times when air came in
  contact with lime water it will produced a cloudy
  solution.
• This air was baptized as Fixed Air
• We now know it as CO2 (carbon dioxide).

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Types of AIR

• There were other times when air led to fiery
  explosions.
• This type of air is referred to as explosive
  air
• It is now known as Hydrogen
• Air at times produce very noxious odors.
• Thus, it was referred to as noxious air
• This one is now known as Nitrogen
• We are missing one type of air that is very
  important.

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Where did the OO go?

• Oxygen was discovered while experiments with
  mercury (I) oxide were performed.
• As HgO is heated a separation of the elements
  takes place resulting in liquid mercury and
  gaseous oxygen.
• As the experiment was concluded a smoldering
  piece of wood burst into flames, hence Oxygen was
  known as flammable air, as the just heated HgO
  sample was placed close by.

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Laws of Mass

• We are all familiar with the Law of Conservation
  of Mass
• Matter can not be created nor destroyed
• While this notion is very familiar to us it was
  not until the 1700s that it was actually stated
• Any mass gained by a substance in a process
  comes from the surroundings

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Conservation of Mass

• We all know now that no matter what we do it is
  impossible to make something out of nothing.
• We must have the atoms available to build an
  item.
• Matter cannot be created nor destroyed reads
  the Law of Conservation of Mass.
• This means that the final product in a reaction
  MUST weigh the same as the starting material.
• Then why is it that sometimes we seem to violate
  this law?

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Rusting of a Nail

• Grab a brand new nail and just to be on the safe
  side clean it up with sand paper.
• Measure the mass of the clean nail.
• Then place the nail out in the open for 5 days.
• Re-measure the mass of the now rusted nail.
• Why does it weigh more than before?
• Have we violated the LAW?

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Sugar is sugar

• There is a second law associated with matter.
• It makes sense that no matter where you obtain
  your sugar you will expect to get the same,
  sugar.
• And the Law of Definite Compositions states
  just that.
• No matter where the sugar comes from it will
  contain 6 atoms of carbon 12 of hydrogen and 6 of
  oxygen (C6H12O6)

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Methane vs Propane

• There are times when the same two elements may
  mix in different mass ratios.
• In these cases the ratio difference is small and
  it will be given using a whole number.
• It is impossible to have fractions since we
  cannot break apart atoms.
• Natural Gas is CH4 and Propane is C3H8
• This is the Law of Multiple Proportions

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Atomic Theory

• When the three mass laws come together they yield
  Daltons Atomic Theory.
• Dalton revolutionized science by treating the
  atom as the component of substances.
• The theory is based on 4 simple assumptions,
  these assumptions are referred to as the Atomic
  Theory Postulates.

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Postulates of Daltons Atomic Theory

• Postulates of Daltons Atomic Theory

• Atoms are the smallest unit of matter. An atom is
  an extremely small particle of matter that
  retains its identity during chemical reactions.
• Atoms of Element A cannot be converted to Atoms
  of element B
• Atoms of the same element are identical. Each
  atom of an element has the same properties. Mass
  is one such property. Thus the atoms of a given
  element have a characteristic mass.
• A compound is a type of matter composed of atoms
  of two or more elements chemically combined in
  fixed proportions.

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Atomic Theory Revisited

• Postulate 1 atoms are the smallest component of
  matter
• Not true, smallest are protons/electrons and
  neutrons, but the atoms are the smallest body to
  retain unique identity
• Postulate 2 Atoms of cannot be converted to
  another element.
• Not true, nuclear reactions allows us to do just
  that

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Atomic Theory in Present Times

• Daltons theory has not been able to withstand
  all the experiments performed since it was
  introduced.
• The problem with the theory is that it is too
  simple.
• Yet it was revolutionary in its own time.
• The Theory tells us about simple ratios of
  elements in compounds but it does not tells us
  why.
• The theory does not explain charged particles

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New Experiments and the Atomic Theory

• Since Dalton introduced Atomic Theory new
  experiments have been performed
• Alpha radiation which lead to the discovery of
  the nucleus
• Nucleus is 10,000 x smaller than the atom
• Nuclear reactions have been performed
• Isotopes were discovered

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Atomic Theory of Matter

• A chemical reaction consists of the
  rearrangements of the atoms present in the
  reacting substances to give new chemical
  combinations present in the substances formed by
  the reaction.
• Atoms are not created, destroyed, or broken into
  smaller particles by any chemical reaction.

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Atomic Theory Revisited

• Postulate 3 atoms of the same element are
  identical
• Not true, isotopes of elements have been
  discovered where the number of neutrons may vary.
  
• Postulate 4 Ratio of elements in a compound is
  specific.
• Still true
• While the model was too simple it has been a
  great starting point.

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Chemical Formulas

• Chemical formulas are just a quick way of
  bookkeeping.
• They are a quick way to tell us what elements and
  how many atoms of each compose a substance
  (compound)
• Elements the simplest form of substance, they
  cannot be broken down into simpler forms (covered
  before).

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IONS

• Ions are compounds or elements where the number
  of electrons and protons do not equal each other.
• Whichever particle is present in higher amounts
  gives the sign of the charge the ion has.
• The magnitude of the difference is equal to the
  charge carried by the species

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Ion example

• In the case of OH, the oxygen provides 8 protons
  and the hydrogen 1. Therefore, a neutral species
  will contain a total of 9 protons and 9
  electrons.
• However, OH-, contains 10 electrons and the same
  9 protons
• Electrons are present in excess therefore, the
  species has a (-) charge. The difference is 1
  hence the charge is (-1).

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Charges on ions

• Note that while the charge of the ion depends on
  which particle is present in greater quantity, it
  is impossible to lose or gain protons.
• A positive charge ion has more protons than
  electrons because it has lost e-s.
• A negative charge ion has more electrons than
  protons because it has gained e-s.

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Types of Ions

• There are two types of ions
• Monoatomic in which an elemental atom looses or
  gains electrons.
• Polyatomic in which a molecule (many atoms) gain
  or loose electrons.
• All polyatomic ions except 1 are negatively
  charged. (Ammonium ion NH4)
• Which polyatomic ions should I know?
• PO43-, SO42-, SO32-, CO32-,NO3-, NO2-, OH-, CN-
  and NH4

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Mass of compounds

• How do we compare/measure compounds?
• Does a dozen eggs weigh the same as a dozen cars?
• Of course not
• But somehow they seem to be the same right?
• When it comes to compounds we use a unit we call
  the MOLE

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MOLE

• A mole of compound A has the same number of
  molecules as a mole of compound B. (just like the
  dozen eggs is the same number as a dozen cars).
• In order to figure out how much a mole weighs we
  use the atomic mass of each atom in the compound.
• H2O 2 Hydrogen x 1.01g 1 Oxygen x 16.0g
• A mole of water weighs 18.0 grams.

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The Periodic Table

• How is the Periodic Table constructed?
• There are many ways to answer this question.
• But the real answer might be the most obvious.
• PERIODICALLY!!!
• Ok so Periodically but what does it mean to be
  periodical?

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What is a period?

• A period is something that repeats itself in a
  given interval.
• We will talk more about periods in the next
  section.
• The periodic table can be said to be organized by
  the number of protons in the nucleus of elements.
  (Atomic Number)
• It can also be said that it is arranged more or
  less by atomic mass.

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What is the real answer?

• As a Physical Chemist in the 21st Century I can
  tell you that it is arranged according to the
  electron configuration of the elements.
• Uhm can you pass that through me one more time?
• The periodic table is arranged according to the
  number of electrons in the outermost shell in an
  atom of each element.
• For the average person that means what?
• Ok, Ok it has to do with the number of electrons.

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Thats Yiddish to me!!!

• Imagine if I have my original response back in
  the 1800s!!!
• I would had been handed my Hemlock and told to
  make a toast to Socrates.
• There were no electrons back then
• Lets go back and take it from the 1800s forward.
• Periodic there are patterns
• Lets take several elements and react them.

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Periodic Chart in the Beginning

• Take for example Sodium and react it with any
  other element you can find.
• Uhm Na and a series of other elements ( F, Cl,
  Br, I) react in a 11 ratio.
• Therefore, F, Cl, I and Br must be grouped.
• Replace Na with K, Li or Cu and the same is true.
• Therefore, Na, Li, Cu and K belong in the same
  group.

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Periodic Chart in Beginning

• Wait a second Cu is not grouped with Na anyway
  you may look at the periodic table.
• This is true!!!
• A second set of experiments paired the elements
  with water
• Na, K, Li react violently with water.
• Cu cant care less about the water
• It is obvious then that Cu does but does not
  belong with Na, K, and Li.

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Mendelev and the Table

• The first periodic chart was introduced by
  Mendelev in 1872. It contained 40 elements.
• In his chart Mendelev left blank areas for what
  he said will be elements that will eventually
  will be discovered.
• Not only did he expected these elements to be
  discovered but he also predicted what their
  properties were going to be.

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The Periodic Table

• The Periodic table consists of
• Periods
• Groups
• Blocks
• Families

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The Periodic Table

• Metals
• Metallic Characteristics
• Shiny
• Malleable (hammer into shape)
• Ductile (made into wires)
• Form () ions
• Non-metals
• Lack Malleability and ductile ability
• Form (-) ions

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The Periodic Table

• Metalloids
• Some of both characteristics
• Noble Gases
• Do not want to reacthence NOBLE
• Halides
• Greek for salt
• They form binary compounds with atoms from group
  IA and they are often referred as salts.

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The Periodic Table

• Alkali Metals
• Alkalibasic solution
• The metals in this group when placed in water
  produced basic solutions
• Alkaline Earth Metals
• The oxides of these metals when placed in water
  produce basic solutions.
• The metal oxides are the most abundant minerals
  of these metals in the EARTHs crust.

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The Periodic Table

• Transition Metals
• There is small changes in reactivity between them
  but they transition us from the s-block to the
  p-block in which there is a big difference in
  reactivity.
• Contain most of the industrial metals
• Cu, Ag, AU, Fe, Ni, Zn, Pt, Pd.
• Inner Transition Metals
• Most are man made and hence contain elements
  involved in nuclear reactions.