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CHEMISTRY

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Title: CHEMISTRY


1
CHEMISTRY
  • Chemistry is a huge topic. You will be asked to
    do lots of worksheets, problem solving. You will
    take quizzes and tests. You will be asked to
    memorize important material, There will be video
    presentations and MAYBE a trip to the chem labif
    it can be arranged.
  • Chemistry is the study of the composition of the
    universe.
  • It studies what the world is made of!
  • Chemistry began not so much as a science as it
    was a pseudoscience.
  • A pseudoscience is a false science.
  • If we argue that true science requires a search
    for the truth via the use of the scientific
    method, the quantification of knowledge that it
    is published and available to all then a
    pseudoscience does NOT do those things and thus
    is a FALSE (pseudo) science.
  • False studies like UFO claims, phrenology and
    astrology are examples of pseudosciences. They do
    not follow the scientific method, their work
    cannot be isolated to one variable, it cannot be
    duplicated, it is not scrutinized by members of
    the international scientific community, etc. etc.
  • There are rules and scientists must play by the
    rulesso must studies that claim to be sciences.

2
Alchemy
  • It turns out that a core true science like
    chemistry started out really as a pseudoscience
    called alchemy.
  • Alchemy is all about the search for two things
  • 1. The elixir of life
  • 2. The process that would turn anything into
    gold.
  • It was all very secret, coded, symbolic. This is
    truly the antithesis of a true science.
  • Those of you into Harry Potter and the LORD OF
    THE RINGS, into wizards and spells and the like
    are all drawn from the stereotypes of ALCHEMISTS.
    Wizards who knew magic were alchemists who knew
    something of chemistry but werent willing to
    share the know-how with anyone else.
  • They never found the elixir of life.
  • They never could spin straw into gold as
    Rumplestiltskin tried to do.

3
The journey from alchemy to chemistry
  • Along the way as wizards and magicians and the
    like tried to find the elixir of life and a way
    to turn anything else into gold, they learned a
    lot of other things, they invented a lot of
    equipment and they began to find the real world
    as interesting a search as the search for the
    elusive.
  • We still use a lot of the glassware they
    invented, we still use a lot of the processes
    they pioneered.
  • Alchemists became chemists when they began to
    write things down in the vernacular, when they
    studied the world around them and when they began
    to publish their results so their peers could
    scrutinize and duplicate.

4
Soin chemistry
  • The study of chemistry begins with the base of
    operations, the bible for all chemiststhe
    Periodic Table of Elements.
  • Without exaggeration I can say that on a single
    piece of paper there is a list of EVERYTHING IN
    THE UNIVERSE. THERE IS NOTHING ELSE.
  • Notice various Periodic Tables. What differences
    among them do you notice?
  • They are merely cosmetic, merely a function of
    the date of publication.
  • I will offer 50 EC points if you can name one
    thing that is NOT on an updated periodic table.

5
Editing a periodic table for use in this class
  • Miss Malley will give you a copy of a Periodic
    Table that we will use in this classroom.
  • We will mark the stepline.
  • We will distinguish between columns and rows.
  • We will number the rows from 1-7 and explain
    their significance.
  • We will number the columns from 1A-8A and explain
    their significance.

6
Dmitri Mendeleev
  • The Father of the Periodic Table was the
    Russian Dmitri Mendeleev.
  • Among others, he tried to organize stuff.
  • Mankind has always liked to organize in order to
    control, to understand. So, look around this
    room. Look at all the different things. How would
    you begin to classify, organize, inventory
    everything in this room. What plan would you use?
    How would you visually design the inventory so
    that you could easily find some item, any item?
    That was the challenge of chemists. They studied
    things all thingshow would one BEGIN to
    organize EVERYTHING?

7
Atomists
  • Eventually it came to be that scientists agreed
    that everything was made of atoms.
  • Whats an atom?
  • Well, a few thousand years ago men speculated
    about the smallest particle that made up all
    things. A Greek by the name of DEMOCRITUS was
    among them. What he speculated was that if you
    took a chunk of something, anything, and you cut
    it in half and in half and in half and in half
    etc. eventually you would come to the smallest
    particle that could not be cut, the tiny
    fundamental marble-like particle he called
    atomos.
  • Atomos is Greek for indivisible, not
    divisible.(not invisibleinDIVISible.)

8
Atoms
  • If everything is made of atoms then what makes
    gold different from oxygen and zinc different
    from lead. Were there different ATOMOS?
  • By the 20th C we realized the atom was NOT
    indivisible. The atom itself had parts
  • Every atom was made up of smaller particles,
    protons, neutrons, electrons.
  • We thought they were indivisiblecould not be
    cutthen we found quarks. Quarks are even smaller
    particles that make up P.N.e.
  • So, what is the smallest, indivisible particle??
  • Havent found it yet.

9
And what IS the difference between gold and
oxygen??
  • On the P.T. there are 2 numbers that identify
    every element. The smaller of the 2 numbers is
    called the ATOMIC NUMBER. This number identifies
    the element. This number is the number of protons
    in the element.
  • So Li has..
  • Gold has
  • Oxygen has.
  • Sodium has..
  • The difference between Lithium and Gold is the
    number of protons in each atom of the element.

10
What about the bigger number?
  • The larger of the 2 numbers is called the ATOMIC
    MASS NUMBER in most books, but in some texts it
    may be called the ATOMIC WEIGHT.
  • The larger number is the TOTAL number of Protons
    and NEUTRONS.
  • Neutrons and protons are jammed together in an
    area called the nucleus.
  • Neutrons have NO electric charge. Protons have a
    POSITIVE electric charge.
  • All protons have the same positive charge so they
    do NOT want to stay close togetherlike charges
    repelthey would fly apart if they could BUT
  • Like cowboys herding cattle, neutrons keep the
    protons in the nucleus. So there is this dynamic
    tension in every atom. Electrons spinning,
    protons and electrons pulling on one another
    while the protons in the nucleus are repelling
    one another.

11
And where are the electrons?
  • We said there were 3 common particles that make
    up every atom, Protons, Neutrons and electrons.
  • Electrons are very tiny.
  • They orbit the nucleus of every atom.
  • Protons and Neutrons are in the nucleus, in the
    CENTER, electrons spin in orbits around the
    center nucleus.
  • The number of electrons is the same as the number
    of protons in every atom.
  • The NUMBER OF PROTONS equals the NUMBER OF
    ELECTRONS.

12
Electron orbits
  • Electrons spin around the nucleus not unlike
    planets around the sun. Electrons travel at
    different distances from the nucleus just like
    some planets are closer or farther from the sun.
  • There are rules for placing electrons in orbit
    around the nucleus.
  • 1. Only 2 electrons can fit in the first energy
    level, the first orbit.
  • 2. UP to 8 electrons can fit in the second energy
    level.
  • 3. Up to 8 electrons is stable for electrons in
    the third energy level.
  • 4. But keep in mind that the number of electrons
    you must distribute is equal to the number of
    protons that identify the element.

13
Atomic models
  • We cant see an atom, not even today with all of
    our equipment. The best we can get is just a
    blur. So over the years scientists have developed
    models which try to give us a picture of what an
    atom looks like.
  • How do we know if they are good models?
  • Accurate?
  • The models are good if we can make predictions
    based on the model and real matter behaves just
    the way we predict they will behave according to
    our model.
  • Over the years there have been many models.
  • We could start with Democritus who said the
    atomos was the indivisible particle.

14
Daltons model
  • John Dalton was a teacher.
  • Over time he studied the behavior of matter and
    suggested his verbal model of the atom.
  • Dalton also thought the atom was
    atomosindivisiblea hard marble
  • BUT
  • He went on to suggest several new ideas
  • 1. Atoms of the same element are all alike.
  • 2.Atoms of different elements are different.
  • 3. Atoms of different elements can join together
    in small whole number ratios to form compounds.

15
Thomsons model
  • JJ Thomsons model of the atom included the newly
    discovered particle called the electron.
  • The electron was discovered in the cathode ray
    tube near the turn of the century. Its discovery
    proved the atom was NOT indivisible but had
    parts. There were SUBATOMIC particles.
  • Thomson reasoned also that since most matter was
    neutral, if this negatively charged particle
    existed then a positively charged particle must
    also exist to make matter neutral.
  • He envisioned the atom to be like chocolate chip
    cookie dough. The dough was the positive part of
    the atom and the chocolate chips were the
    electrons.

16
Dr. Rutherford said
  • Rutherfords model of the atom came about as a
    result of an elegant experiment in 1911 called
    the gold foil experiment.
  • He had engineers pound a bit of gold until it was
    VERY thin. He fired POSITIVELY charged particles
    into this gold foil.
  • 99.999 of those particles went through the
    foil unhampered. Straight through.
  • Once in awhile a particle would come bouncing
    straight back at him.
  • Once in awhile a particle would be deflected
    off at some angle.
  • What the world realized was that the atom was
    made of a charged, very dense, very SMALL
    nucleusa center. The electrons must be outside
    that nucleus somehow. And in between the nucleus
    and the negative electrons there was NOTHING!!!
  • It was Rutherfords gold foil experiment that
    began to suggest that the world was really an
    illusion, that the world was mostly made of EMPTY
    SPACE.
  • Everything is made of atoms and the atom is
    99.999 empty space thus everything is
    mostly..
  • His experiment also proved that most of the mass
    was in the nucleus. Electrons contributed
    insignificant mass to the atom.

17
Niels Bohr
  • In 1913 Niels Bohr (Danish) suggested another
    model. This is the one most useful to us.
  • In the Bohr atom, the nucleus contains protons
    and neutrons.
  • The electrons orbit the nucleus in orbits at
    different distances like planets orbiting the
    sunthey dont all orbit in the same path but are
    spread out some closer to the sun, some farther.
  • Electrons are like that.
  • It turns out that because matter is neutral, the
    number of positive charges (P) must be equal to
    the number of negative charges (e-).
  • Over the years we have realized that 2 e- can
    spin in the closest orbitcalled an energy level.
  • Up to 8e- can orbit in the second energy level.
  • Up to 8 e- can orbit in the third energy level
    and we wont go much beyond that as we sketch
    atoms.
  • One more point, the farther out the electron is
    from the nucleus, the more energy it has. The
    closer it is to the nucleus, the less energy the
    electron has.

18
Sketching atoms
  • We will use the BOHR atom as our model.
  • Niels Bohr developed this particular model.
  • Miss Malley will now turn off the system and we
    will learn how to sketch atoms from 1 - 20.

19
Properties
  • Go to the bulletin board and get the picture.
    Ill give you 10 EC points for the correct one.
  • Butthat would be kind of difficult because???
  • YOU NEED TO NARROW DOWN THE CHOICES
  • YOU NEED MUCH MORE INFORMATIONYOU NEED
    PROPERTIES
  • PROPERTIES ARE WORDS THAT IDENTIFY, DESCRIBE, AND
    DISTINGUISH.

20
Properties identify, describe, select
  • Words that describe and identify and select
    particular objects from among others are called
    properties.
  • They include physical properties
  • Color, odor, luster, state, density, texture,
  • Conductivity, malleable, ductile, magnetic.
  • And there is ONE chemical property
  • The number of electrons in the OEL determines how
    the atom will behave when forming
    compoundschemical reactivity.

21
Properties include
  • Solids , liquids, gases have identifying
    properties.
  • Solids have a definite shape and volume.
  • Liquids have a definite volume but take the
    shapes of their container.
  • Gases spread out to occupy the entire space
    available so gases have neither a definite shape
    nor volume.

22
Things can change
  • It turns out there are two ways that matter can
    be changed. There are physical changes. There are
    chemical changes.
  • Physical changes are any changes you might make
    in an object that do NOT change the identity of
    the object. So you must ask yourself after the
    change is made Did I end up with the same
    substance I started with? If the answer is YES
    then that describes a physical change.
  • If you end up with an entirely different
    substance that has different physical and
    chemical properties than the substanve you
    started with then that describes a CHEMICAL
    change.

23
Physical changes
  • You tear a piece of paper. After you do that you
    still have a paper. You have not altered the
    identity of the substance.
  • If you cut, saw, shred, tear,etc then those are
    physical changes because when you are done you
    still have the original substance.
  • After you melt butter, you started with butter,
    you end up with butter. So freezing, boiling
    melting are all physical changes.
  • A change in density is a physical change.

24
Chemical changes
  • In all chemical changes you will end up with
    something VERY different from what you started
    with.
  • Take some hydrogen, odorless, colorless EXPLOSIVE
    gas and add it to some oxygen, odorless,
    colorless gas that supports combustion (burning).
    After you do that you end up with a clear liquid
    you use to put out fires called water. Water is
    VERY different from EITHER hydrogen or oxygen.
  • Other things that produce very different products
    include baking, cooking, exploding, burning,
    tarnishing, rusting, corroding,all chemical
    reactionsthe forming of compounds, the
    destruction of compounds, the rearrangements of
    compounds, the production of light,

25
Now, back to the P.T.
  • The stepline divides the P.T. into..and.
  • Elements that sit ON the stepline are called
  • The column number tells us..
  • The row number tells us..
  • The atomic number tells us..
  • The atomic mass number tells us.
  • The man who designed the first modern periodic
    table was
  • The difference between gold and oxygen is.
  • The difference between an atom of sodium and an
    atom of lithium is..
  • The smallest part of an element is.
  • The word atom comes from.
  • The atom is made ofcommon particles
  • Consider the differences between metals and
    nonmetals. Characteristics include?
    M

26
Properties of M and NM
  • A metal is generally
  • Solid at room temperature
  • Solid with a luster
  • Malleable
  • Ductile
  • Silvery in color
  • On the left side of the stepline on the P.T.
  • Have fewer electrons in the outer energy level of
    the atom.
  • Likely to give away electrons as compounds are
    formed
  • SOME METALS ARE MAGNETIC
  • Nonmetals are none of those things.

27
More, More of the P.T.
  • Col. IA, Group I are called the ALKALI metals.
    They all have only 1 e- in their OEL and thus are
    looking to get rid of it! They happily form
    compounds with any element in Col . VIIA Metals
    form a 1 ion while the Col. VII halogens form
    a -1 ion.
  • Col.I Col. VII produce SALTS.
  • Every element in Col IA is soft, silvery, low
    density, melt at low temps and highly REACTIVE

28
And Col IIA
  • These are called the ALKALINE EARTH METALS
  • They all have 2 e- in their OEL so that they try
    to get rid of 2 OEL e-. Thus they are very
    reactive, eager to form compouhnds, but not
    kquite as eager as those in Col IA since these
    elements are closer to achieving 8 e- in the
    OEL.
  • Col. IIA metals will form compounds very easily
    with those elements in Col VIA.

29
Transition elements/metals
  • Groups 3-12 is that big middle group of metals.
  • These do not follows the rules quite as nicely as
    the Col. A elements.
  • These metals are mostly shiny, have high melting
    points, are good conductors of heat and
    electricity. They make ionic compounds with
    nonmetals.
  • These metals are often found in ores dug out of
    the ground.

30
RARE EARTH ELEMENTS
  • These are metals that were pulled out of the main
    P.T. and put at the bottom in two row. This was
    done both because the elements are rareyou
    probably wont run into any of these in your
    lifeANDbecause it made the table able to fit on
    a single piece of paper.
  • The two rows were called the Lanthanide and
    Actinide series.
  • Generally Lanthanides are from 51-71 though this
    may vary slightly on PT
  • Generally the Actinides are 90-103.
  • Keep in mind that the last naturally found
    element is 92 Uranium beyond that the elements
    are man made by bombarding large nuclei with one
    more Protonrecall that it is the number of
    protons that identify the element.

31
Col IIIA
  • This is claled the Boron Group only because Boron
    is the first element in the col. On some PT it is
    col 13.
  • Boron is a metalloid. It is brittle,black.
  • Every element below Boron is a metal though, just
    to the left of the stepline.
  • The most common metal that comes from the earth
    is Aluminum in this group.

32
Col. IVA
  • Called the Carbon group. Carbon is clearly a NM
    But Si is a metalloid, it sits ON the stepline.
  • Silicon compounds make up 60 of the Earths
    crust.
  • Tin and lead are both metals.

33
Col. VA
  • Called the Nitrogen group.
  • Nonmetal, N is a diatomic element that is 80 of
    our air..it also fills the tires of airplanes. It
    does not combine easily with other elements.
    Nitrogen is part of our bodies in proteins.
  • Other elements include P, a NM
  • Arsenic is a poison.
  • Sb, Bi, are both metals.

34
Col. VIA
  • The oxygen group is very important to usto
    breathe. It only make sup 20 of the air but
    essential. Most oxygen is combined with Silicon
    in rocks.

35
Col. VIIA
  • Halogens.
  • Col. 7A elements are salt formers. They love to
    make salts with metals in 1A.
  • These are all very reactive nonmetals. Fluorine
    is the MOST reactive of all the nonmetals.

36
Col. VIIIA
  • The Noble gases are all in col 8A.
  • Group 18
  • These gases are used in signs.
  • These gases have 8 e- in the OEL and thus are
    stable and thus make NO compounds with other
    elements.

37
Hydrogen
  • Notice that Hydrogen is set off by itself. It is
    often set above Col 1A.
  • H is a NONMETAL
  • It is a diatomic gas nonmetal
  • BUT
  • We put it in Colo. IA usually because it has 1 e-
    in its OELits ONLY ELand thus behaves a little
    like the elements in Col IA.
  • It loses its 1 e- a lot!
  • Hydrogen is the most abundant element in the
    UNIVERSE.

38
ISOTOPES
  • It turns out that
  • Atoms of the same element have the same number
    of protons in the nucleus.
  • Recall that the number of protons identifies the
    element.
  • Element number 3 is .because..
  • BUT.
  • It also turns out that
  • Although every atom of a particular element has
    the same number of protons, atoms of the same
    element can have different numbers of neutrons.
  • For example although every atom of oxygen
    has.protons, one atom of oxygen might have 7
    neutrons, another atom of oxygen might have 8
    neutrons, another atom might have 6 neutrons. So
    there are 3 isotopes of oxygen in this example3
    isotopes, 3 versions of oxygen as it were..
  • Carbon has .protons and.electrons. BUT some C
    atoms have 6 neutrons but other C atoms have 8
    neutrons. So we would say that carbon has two
    isotopes2 versions of carbon.
  • You couldnt tell the difference among isotopes.
    They chemically behave identically.

39
So what
  • So what is the periodic table?
  • What is an element?
  • An element is a collection of atoms that all look
    alikeall have the same number of protons.
  • An element is the fundamental building block of
    everything else.
  • ALL things are either elements or compounds.

40
And a compound is.
  • A compound is a collection of 2 or more elements
    that have joined together to make something BRAND
    NEW.
  • EVERYTHING then is either an element, on the
    periodic table or it is a collection of elements.
  • Gold is an element. Water is a compound. Whats
    the difference?

41
Elemental symbols and chemical formulas
  • On the P.T. every element has a symbol of 1 or 2
    letters. Sometimes the symbol makes sense.O is
    oxygen. But Na is sodium because the symbol Na is
    from the Latin word Natrium.
  • N is nitrogen but Hg is from the Latin
    Hydrargyrum which is Latin for Mercury.
  • It is wise to learn the symbols of the most
    common elements since it will save you time in
    the long run.
  • Compounds can also be written with shorthand
    symbols. NaCl is sodium chloride. H2O is water.
  • We will talk much more about compounds as we move
    on.

42
Why do elements form compounds at all?
  • It turns out that compounds form at all because
    Nature Seeks Stability.
  • So what does nature think is stable?
  • Nature plays by something called the octet rule.
    That means that an atom is considered chemically
    stable if it faces the world with 8 e- in its
    outermost energy level.
  • Atoms want 8 e- in their outer energy level.
  • They will do whatever it takes to get a full
    outer energy level to face the world.
  • It turns out that atoms can gain or lose
    electrons in order to face the world with a full
    OEL.
  • Miss Malley will spend a good deal of time
    lecturing further on the how and why of compounds.

43
Three types of compounds.
  • An atom will do whatever it must in order to get
    a full outer energy level facing the world.
  • Metals in Col. I, II, III have 1,2,3 e- in the
    OEL so it is easier for the atom to LOSE 1 or 2
    or 3 e- than it is for them to pick up 7e-, 6e-
    or 5e-.
  • Nonmetals have 5,6,7 or 8 e- in their energy
    levels for Col. V, VI, VII, VIII. It is easier
    for those elements to pick up 3 or 2 or just 1 e-
    than to try and give away 5 or 6 or 7 e-. So NM
    want to GAIN e-.
  • Col IV elements have no advantage in either
    gaining or losing e- so we will discuss their
    UNIQUE situation later.
  • Col. VIII elements already HAVE 8e- in their OEL
    so they need nothing! Therefore they do NOT make
    compounds.
  • Compounds are made because atoms seek stability,
    they seek a full OEL facing the world.
  • Col. VIII A elements already have 8, they are
    stable, they are full, they do NOT form
    compoundsthats why some books call them the
    INERT gases. Col 8A elements are all gases and
    the word INERT describes and object that does
    NOTHING!
  • If someone says you are inertthat is not a
    compliment.
  • Some books call Col. 8A elements the NOBLE gases.
    Nobility means royaltyand the royals do not
    associate with the masses.do not mingle with
    others.so they do not form compounds.

44
IONIC compounds
  • Atoms gain stability by joining with other
    elements, other atoms so they have a full OEL.
  • Atoms will gain or lose the number of electrons
    that will give them the full OEL.
  • So when a metal atom seeks to lose some e-, a
    nonmetal that wants to pick up that number of e-
    will join with it to produce a COMPOUND
  • This is an IONIC compound. An ionic compound is a
    METALNONMETAL.

45
Covalent Compounds
  • Covalents compounds are sometimes called
    MOLECULAR compoundsthey mean the same thing.
  • A covalent compound is made up of 2 NONMETALS.
    When a Nonmetal and a Nonmetal join one is not
    strong enough to pull off e- from another NM. And
    NM dont really want to give away any e-. So what
    happens when a NM and a NM join is the e- are
    shared between them so that each of the atoms has
    influence over 8e-.
  • This produces a compound called a covalent
    compound.

46
What follows this will be the naming of
compounds, the definition of ions, polyatomic
ions and the PAI compounds, the binary and
ternary rules, writing formulas and predicting
compound formation.
47
Whats an ION
  • Atoms will gain or lose electrons in order to
    achieve a full OEL facing the world.
  • The definition of an atom includes the notion
    that the number of Protons the number of
    electrons in every atom.
  • BUT
  • When at atom wither gains or loses electrons then
    the number of Protons NO LONGER equals the number
    of electrons.
  • And THAT is an ion. An ion is an atom thqt has
    lost or gained electrons. An ion has an electric
    charge. It either has more electrons that protons
    so it has a NEGATIVE chare OR it has fewer
    electrons that protons so that it now has a
    POSITIVE electric charge.
  • Atoms are NEUTRAL.

48
Binary ionic compound
  • A binary ionic compound
  • This is a compound made of 2 elementsbinarytwo.
  • Ionic means this is a metal attached to a
    nonmental.
  • Compound is two or more elements making something
    very new and different so that atoms will become
    more stable.
  • The metal wants to give away electronas and the
    nonmetal gains those electrons.
  • In writing ionic compound formulas OXIDATION
    NUMBERS must equal zero.THIS WILL REQUIRE A LOT
    OF PRACTICE
  • Oxidation numbers tell us how the atom will
    behave when forming compoundsit tells us how
    many electrons it wants to gain or lose.
  • Name the metal, name the root of the nonmetal and
    end the compound in IDE
  • Sodium chloridesodium is metal and chlor is root
    of NM and we end the binary name in IDEsodium
    chloride.
  • Calcium chloride.
  • Magnesium oxide

49
Binary Molecular compounds
  • Nonmetal attached to another nonmetal is a BMC.
    This is where Nonmetals SHARE OEL e-. In ionic
    compounds one atom loses electrons and the NM
    gains electrons. BUT in BMC no aytom gains or
    loses electrons. The two nonmentals simply SHARE
    electrons so that eacha tom has influence over
    enough electrons to make them more stable.
  • We name the first nonmetal, name the root of the
    second nonmetal and end the name in IDE. ALL
    binary compounds end in IDE.

50
MIXTURES
  • There are elements which are pure substances,
    fundamental, basic, and made of all the same kind
    of atom. Hydrogen, oxygen , sodium , chlorine
  • There are compounds which are pure substances
    made of 2 or more types of atoms joining together
    to make something new in order to achieve a full
    OEL facing the world. Water , salt
  • Mixtures on the other hand are NOT pure
    substances. Mixtures do not require a recipe. A
    mixture is just a collection of stuff thrown
    together with no particular quantities required.
    No electrons are involved. All parts of a mixture
    keep their own identities. Nothing new is made.
    Salt water. Tossed salads stew vegetable soup

51
Homogeneous vs Heterogeneous
  • Substances, elements, compounds, mixtures can be
    described as either homogeneous or heterogeneous.
  • Homogeneous describes any substance that has the
    same composition throughoutno matter where you
    take the sample it will be the same as every
    other sample. So elements are homogeneous. All
    atoms of an element are the same. Water is a
    compound. Compounds are homogeneousevery
    spoonful of water is the same no matter where the
    sample is from. All NaCl molecules are the same.
  • Mixtures might also be homogeneous. Cream mixed
    into coffee produces an evenly mixed mixture. No
    matter where the sample is taken in that ocoffee
    cup the sample with be the same. Salt water is
    homogeneous, the salt is evenly distributed
    throughout the water. .All solutions are
    homogeneous mixtures. Solutions involve a SOLUTE
    mixed into a SOLVENT. The solvent DISSOLVES the
    solute until it is evenly mixed. The word
    DISSOLVE means to break into tiny pieces..
    Breaking is a physical changeso a solution is
    just a mixturea physical event.Not a chemical
    reaction
  • So all elements, all compounds and SOME mixtures
    can be described as homogeneous
  • Heterogeneous describes only mixtures. It
    describes mixtures that are NOT evenly mixed so
    that every spoonful is different. This would be
    a tossed salad, vegetable soup, chocolate chip
    cookies., stew. Each sample would be different.

52
ALLOYS
  • An alloy is a solution, a mixturea very specific
    mixture of metals melted together.
  • We will make a list from the chemistry texts but
    alloys include steel, pewter, solder, brass, 24
    karat gold
  • But it is just a mixture. Not a compound. No
    recipe is requiredjust a homogeneous solution

53
CHEMICAL REACTIONS
  • 1. Chemical reactions produce chemical changes.
  • Chemical reactions can be written in shorthand
    using an equation form.
  • We begin with REACTANTS and we end up with
    PRODUCTS.
  • Products are VERY different from the reactants we
    started with.
  • BUT everything must be accounted for. All the
    elements on the left must equal the elements on
    the right.
  • Evidence that a chemical reaction has taken place
    include forming a precipitate, color change,
    formation of a gas, change in temperature.
  • If heat, light or energy is given off then we
    call that an EXOTHERMIC REACTION. Things get hot.
  • If heat is absorbed into the chemical reaction
    then we call that an ENDOTHERMIC REACTION.
    Things get Colder.

54
Keep in Mind
  • In chemical reactions, the energy is not in the
    atoms themselves but it is in the BONDS that are
    formed or broken. As when you digest food. It
    isnt the Atom itself you are really interested
    in, it is the energy stored in the atomic bonds
    that hold different atoms together. When bonds
    are formed, broken or rearranged it is the energy
    required to do that that is stored in or released
    from that action. And THAT is what we are after.

55
Reactants yield Products
  • In chemical equations reactants must equal
    products. Energy is always involved.
  • All chemical equations must be balancedthe law
    of conservation of mass and energy is the rule.
    You cannot end up with more or less than what you
    started with and you cannot end up with different
    elements than what you started with.
  • We balance chemical equations by using
    COEFFICIENTS. Coefficients are whole numbers we
    can place in front of compounds or fee standing
    elements. They cannot separate a compound, they
    must be IN FRONT OF wither the element or the
    compound.
  • We learned that when writing a proper chemical
    formula, subscripts were essential to the recipe.
    The recipe for water or sugar or carbon monoxide
    or sulfur dioxide is ALWAYS the same. The
    subscripts are there to tell us how many of each
    atom we need to make a molecule of a compound.
    SUBSCRIPTS do not change. The recipe for water is
    ALWAYS the same.
  • SO
  • When you go to balance chemical equations you may
    NEVER NEVER EVER NEVER change a subscript in
    order to balance a chemical equation.

56
We will now practice balancing a LOT of chemical
reaction.
  • It is like solving a puzzle.
  • Some of you will do well, others of you will
    struggle.
  • There are no hard and fast rules except
    ONEwhatever is on the left of the equation must
    equal whatever is on the right.
  • So when you ask Miss Malley, is this right? I
    will answer count!!! Just count!!!
  • Lets try some.

57
There are 5 common types of Chemical reactions.
  • 1. Synthesis reaction.
  • From simple to complex.
  • AB AB Two simple reactants, substances, join
    together to seek stability at the OEL e-. The
    product is a more complex compound.
  • 2. Analytical reaction. When your English teacher
    asks you to analyze a poem, what do you do? Dont
    you take it apart and look at it line by line,
    word by wordsee what its made of? So Analysis
    is to take apart, look at what is is made of.
  • So in chemistry we start with a complex compound
    and tear it apart, down to its simpler building
    blocks.
  • AB AB

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Single replacement reactions
  • 3. The third type of chemical reaction is just
    thisa single replacement reaction.
  • A BC AC B
  • Bill and Cynthia go to the dance. Antonio goes to
    the dance aloneuh oh,
  • Poor Bill has been replaced by AntonioAntonio is
    taking Cynthia home.
  • One element replaces another element in a
    compound.
  • We start out with a compound and a free standing
    element. We end up with a different compound and
    a different free standing element.
  • AB C CB A

59
Double replacement reaction
  • 4. Double replacement reactions look the most
    complicated.
  • Reactants are two compounds, products are two
    different compounds.
  • Two couples go to a dance and everyone changes
    partners.
  • AB CD AD CB

60
Combustion reaction
  • 5. The 5th chemical reaction is combustion which
    means burning.
  • It is EASY to spot because the products are
    always the same.
  • We start with some Hydrocarbon compound we add
    oxygen and the products are always carbon dioxide
    and water!
  • Miss Malley will now give you a lot of examples
    for you to identify.

61
A few more terms to know
  • In chemical reactions there is always some energy
    echange involved, absorbed or given off.
  • There is something called activation energy. That
    is the energy needed to start a chemical
    reaction, give the reactants a nudge to get them
    started.
  • A push on the sled. A push to start a skateboard.
    A match to light a fire.
  • A CATALYST is a substance often used in chemical
    reactions. A catalyst is a substance that speeds
    up a chemical reaction but does not get involved
    directly. Your friend fixes you up with someone
    but your friend does not go the date! Your
    friend brings two people together and then steps
    back. So thats what a catalyst does in a
    chemical reaction. Speeds up the reaction but in
    the end is not PART of the reactants.
  • Enzymes are excellent examples of catalysts. In
    the human body thats the job of an enzyme to
    speed up reactions, let them take place at a
    relatively low temperature98.6F is not a very
    high temperaturewe cook roasts at 350F. Body
    temperature cannot be too high since
    proteinslike your brainstarts to unravel at
    higher temps. So catalysts are REALLY essential
    in surviving.

62
A huge topic!!
  • There is lots of work to be done. Worksheets,
    videos, projects, quizzes, tests all ongoing and
    upcoming.
  • You will be asked to memorize material.
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