Transcript Slide 1

Chemistry and Society
Types of Matter
&
The Periodic Table
Dr. Victor Vilchiz
VSU
Fall 2006
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
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.
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 wouldn’t 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.
Alchemy’s 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
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Cheo=to cast
• It could had come from ChinaChin-I=gold
making juice.
Where to now?
• So making gold was not possible… now
what?
• The obvious question will be then… why
can’t we make gold?
• The quest to understand what was going
on began and thus modern chemistry was
born.
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.
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).
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.
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.
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 1700’s that it was actually
stated:
– “Any mass gained by a substance in a
process comes from the surroundings”
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?
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?
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)
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”
Atomic Theory
• When the three mass laws come together
they yield Dalton’s 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.
Postulates of Dalton’s Atomic
Theory
Postulates of Dalton’s 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.
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
Atomic Theory in Present Times
• Dalton’s 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
“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
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.
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.
Matter: Physical State and
Chemical Constitution
There are two principal ways of classifying
matter:
By its physical state as a solid, liquid, or
gas.
By its chemical constitution as an
element, compound, or mixture.
Solids, Liquids, and Gases
Solid: Atoms or molecules have a fixed shape.
They can be reshape, malleability, can be made
into wires, ductile. They are relatively
incompressible, fixed volume. (solid example)
Liquid: Atoms or molecules have some
freedom to move around and liquid has a fixed
volume but no fixed shape. Liquids are slightly
compressible. (liquid example)
Gas: Molecules or atoms have freedom to move.
Conforms to container shape but it is not volume
restricted. (gas example)
Molecular representation of a solid.
In a solid
each
molecule is
close to its
neighbors and
restricted to
vibrating
back and
forth around
a specific
location.
Return to Lecture
Molecular representation of a liquid.
In a liquid the
molecules are
close together,
but they can
move past
each other;
each molecule
can move a
short distance
before
bumping into
one of its
neighbors.
Return to Lecture
Molecular representation of a gas.
In a gas the
molecules are
much farther
apart than in
liquids or
solids, and they
move relatively
long distances
before colliding
with other
molecules.
Return to Lecture
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).
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
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).
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.
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+
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
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.
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?
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.
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.
That’s Yiddish to me!!!
• Imagine if I have my original response
back in the 1800’s!!!
– 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 1800’s
forward.
– Periodic = there are patterns
– Lets take several elements and react them.
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 1:1 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.
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 can’t care less about the water
• It is obvious then that Cu does but does not belong
with Na, K, and Li.
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.
The Periodic Table
• The Periodic table consists of:
– Periods
– Groups
– Blocks
– Families
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
The Periodic Table
• Metalloids
– Some of both characteristics
• Noble Gases
– Do not want to react…hence NOBLE
• Halides
– Greek for salt
– They form binary compounds with atoms from
group IA and they are often referred as salts.
The Periodic Table
• Alkali Metals
– Alkali=basic 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 “EARTH”’s crust.
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.
Bonding
• There are three types of bonds
– Ionic: involves the exchange of electrons
and usually occurs between a metal and a
non-metal
– Covalent: involves the sharing of electrons
and usually occurs between two nonmetals or a non-metal and a metalloid
– Metallic: involves the pooling of electron
and involves two metals.
Elements, Compounds, and
Mixtures
Millions of substances have been characterized by
chemists. Of these, a very small number are
known as elements, from which all other
substances are made.
An element is a substance that cannot be
decomposed by any chemical reaction into
simpler substances. (examples)
The smallest unit of an element is the atom.
Elements: mercury, arsenic, sulfur, iodine, magnesium,
bismuth.
Photo courtesy of American Color.
Return to lecture.
Elements, Compounds, and
Mixtures
Most substances are compounds.
A compound is a substance composed of two
or more elements chemically combined.
The smallest unit of a compound is the
molecule.
The law of definite proportions states that a
pure compound, whatever its source, always
contains definite or constant proportions of
the elements by mass.
Elements, Compounds, and
Mixtures
Most of the materials we see around us
are mixtures.
A mixture is a material that can be separated by
physical means into two or more substances.
Unlike a pure compound, a mixture has variable
composition.
Mixtures are classified as heterogeneous if they
consist of physically distinct parts or homogeneous
when the properties are uniform throughout. (see
mixture and separation)
A mixture of potassium dichromate and iron fillings.
Photo courtesy of James Scherer.
Return to lecture
A magnet separates the iron filling from the mixture.
Photo courtesy of James Scherer.
Return to lecture.
Components of Matter
• Element: simplest type of
substance (only 1 type of atom)
• Molecule: a structure containing 2
or more atoms chemically bonded
– Simplest molecule is H2
• Compound: Chemical combination
of two or more elements
• Mixture: Physically intermingled
elements/compounds
Scheme for Classification of
Matter