Understanding our world and being able to use that knowledge to help us means describing things and understanding how they behave.

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Understanding our world and being able to use
that knowledge to help us means describing things
and understanding how they behave.

• What are the ways and words we can use to
  describe stuff?

• How does stuff behave? What does it do when we
  make changes to it?

• Is the stuff one thing (pure) or more than one
  thing (mixture)?

• Once we make changes to stuff what are its new
  characteristics? Can we change new stuff back
  into the old stuff?

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Matter anything that has mass (weighs something)
takes up space (has volume). Matter has 3 forms
or physical states
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Properties can be broken down into two types -
physical and chemical properties. Whats the
difference?
Chemical properties of a pure substance that
describe its ability to combine with or change
into a new substance. Examples
Physical properties of a pure substance, we can
see without changing it into a new substance.
Examples include

1. Flammability
2. Reactivity

1. physical state solid, liquid, gas
2. color
3. shape
4. mass
5. texture
6. melting boiling point
7. density
8. solubility in water

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Matter can either be found in nature as a pure
substance or a mixture. What does it mean to be
pure?

• Pure substance - a substance that contains a
  single type of matter. When the substance is
  pure, it has a unique set of properties

• Example pure water contains ONLY molecules of
  water (H2O) and NOTHING else!! When water is pure
  it has the following properites

• a defined melting point (0 C)

• no color

• a defined boiling point (100 C)

• no taste

• a defined density (1 g/mL)

• does not burn

• Pure substances have characteristic properties
  which we can use to identify the substance

imagine you had a colorless liquid that boiled
at 100 C, melted at 0 C, and had a density of 1
g/mL, you could say it is most likely water!!
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• Mixture - two or more substances mixed together,
  but not chemically combined. Each component in a
  mixture keeps its individual properties.

• Example salt water contains water molecules
  (H2O) and sodium chloride (NaCl) molecules.

• The mixture will behave differently than the two
  materials separate. Salt water will have a
  different boiling point than pure water!

• Because the parts of a mixture are not chemically
  combined, the parts can often be separated
  (purified) into their pure forms by taking
  advantage of their properties.

• Salt can be separated from water by distilling
  the water (heating it to boiling), leaving behind
  salt, collecting water pure as it condenses.

• If you separate salt from water, the two
  substances will have the same properties as they
  would before you mixed the two.

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Some substances are able to dissolve other
materials. If you put sugar into water, the water
will dissolve the sugar. The sugar will soon
disappear (sugar molecules are dissolved in the
water)

• Solubility - the property describing how much of
  a material can be dissolved.

• Pepper is not soluble in water. We can say pepper
  is insoluble in water.

• Solution - a special type of mixture where one of
  the components mixes evenly throughout
  (dissolves) so that you cant visibly see one of
  the parts.

• Dissolving a substance is an example of a
  phyiscal change. The substance is STILL THERE,
  and hasnt been changed into anything new!

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• Mixture -

- If you separate salt from salt water, the water
will have the same properties as it would before
you mixed the two
- BUT The mixture as a whole can behave
differently (salt water will have a different
boiling point than pure water)

• Solution -

• Components in mixtures can often be separated
  (purified) into their pure forms by taking
  advantage of their properties

- Salt can be separated from water by distilling
the water (heating it to boiling), leaving behind
salt, collecting water pure as it condenses
- A mixture containing stuff not soluble in water
could be filtered, leaving behind the stuff that
doesnt dissolve (sand water)
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Pure substance!
only water - pure
Mixture!
ingredients a gas (CO2)
Mixture!
mixture of salts, fish, seaweed
Pure substance!
Sodium Chloride - pure
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Density is the ratio of the mass of an object to
its volume.

• Density is determined by measuring the mass of an
  object, and measuring the volume, then dividing
  the two. Mass is measured in grams (g), volume in
  milliliters (mL).

Density (D) Mass g (M) Volume mL (V)

• Density is a characteristic property of pure
  substances it will always be the same under a
  given set of conditions. Example density of
  water at 25 C is 1 g/mL.

• Objects with lower densities tend to float (cork
  floats in water). Objects with higher densities
  tend to sink (oil floats because it is less
  dense).

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• Lots of things affect density

• Water with salts dissolved in them tend to be
  more dense than pure water. So, salt water (for
  example, in the ocean) will sink to the bottom
  while fresh water will float on top.

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• Ocean water is 3.5 salt. The Dead Sea has a
  salinity of 34!!!! Watch this!

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Lets try to describe matter in some more detail
Matter

• Molecule - a single unit of a pure substance,
  chemically combined (bonded) in a defined ratio.

• Examples water (H2O), hydrogen peroxide (H2O2),
  sodium chloride (NaCl)

• Compound - many molecules of the same pure
  substance. Example a glass of water contains
  many millions of molecules of water.

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• Element - a pure substance consisting of a single
  type of atom

- each element has distinctive properties. Some
are stable, and can be found by themselves in
nature. Others are so reactive, they will only be
found combined with other elements.
- elements cant be broken down further and still
keep their properties
- about 100 different elements
- elements identified by 1 or 2 letter symbols.
Letters often are the first letters of the name
of the element (Chlorine -gt Cl)
- organized in a specific way into the Periodic
Table of the Elements.
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The Periodic Table organizes elements into a set
of patterns, arranged by increasing atomic
number, invented by Russian chemist Dimitri
Medeleev (1869)
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You are probably familiar with certain elements
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Adding other metals (Nickle, Tungsten) to steel
gives different properties.
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• Metals Sodium (Na), Iron (Fe), and Aluminum (Al)

• Shininess, magnetic
• malleability ability of a substance to be
  molded/formed
• conductivity ability of a substance to transfer
  heat/electricity

• Reactivity willingness and ability to combine
  with other elements

- Many of the elements are so reactive that they
are not found alone in nature. Wanna see how
reactive?
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Matter
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• Atoms smallest building block of which matter is
  composed, when combined in specific ratios, they
  make the elements

• Theory of atomic structure says that all atoms
  consist of

Nucleus -
contains protons with a positive charge ()
and neutrons (neutral, no charge)
Electrons -
particles with negative charge (-) orbiting
nucleus in a cloud

• An element is identified by the number of protons
  in its nucleus, called the atomic number.

An atom having 6 protons in its nucleus is a
called a carbon atom
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• Atoms can combine to form a single molecule of a
  new substance. Remember, a molecule is a single
  unit of a substance, combined in defined ratios

• Atoms in molecules are held together by
  attractive forces called bonds.

Sodium - very reactive metal
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• Atoms combining in defined ratios

Hydrogen - very light, flammable gas
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Now that we have described matter and put it into
different catagories, we can describe how matter
changes

• Physical properties characteristic of a pure
  substance that can be observed without changing
  it into another substance.

- water always has a density of 1 g/mL at 25 C
- at atmospheric pressure, water always melts at
0C, and boils at 100C

• Physical changes changes to a substance that can
  be observed without changing its identity.
  Examples

- Change of state, which is easily reversed. For
example, water freezes into ice, boils into water
vapor, but its still water!
- Dissolving a substance into another substance.
Salt dissolves in water, but they are not
chemically combined. They can be separated
(distillation)

• Physical changes are sometimes hard to notice

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• Chemical properties a characteristic ability of
  a substance to change into another substance.

- Sodium metal is very reactive, never found
alone in nature
- Examples of chemical properties flammablility,
reactivity (the desire of a substance to combine
with and form new susbtances

• Chemical changes changes to a substance that
  results in a new substance forming.

• Chemical changes are often much more obvious than
  physical changes

1. Color change

1. Light, heat, or energy released (burning)

1. Gases or solids form where there were none before

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Recall that all pure substances have
characteristic properties that describe the way
they behave, and can be used to identify the
substance.

• Polarity is a property of all substances
  resulting from the unequal sharing of electrons
  in the bonds holding the molecule together

• Example in a water molecule, electrons are found
  more near the oxygen atom than they are near the
  hydrogens. Water is said to be polar.

• So, one end of the moleule has a positive charge
  and one end has a negative charge. This gives
  rise to polarity!

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• In some molecules, electrons are distributed over
  the molecule equally. Such a molecule is said to
  be non-polar.

• We can list substances in order by polarity

Ok, Mr. Johnson Why do we care about any of this?
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We care for a couple of reasons

• Substances with similar polarities dissolve in
  each other

- Water, Ethanol and Acetone can all dissolve or
mix in each other (all polar)

• Substances with very different polarities do not
  dissolve in each other

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Nonpolar hydrocarbons layer on top of each other,
sliding against themselves. This is why oils are
good for keeping things from sticking to each
other (they are slippery and greasy)
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1944 Hartford Circus Fire - Do Now
Briefly answer the following four questions based
on the video Fire Under the Big Top You may use
your notes!

• List any two causes/factors for the Hartford
  Circus Fire.
• What major world event was going on when the fire
  occurred?
• What was the 2-component mixture used to
  waterproof the circus tent?
• Who did the public blame - who was the scapegoat
  - for the fire and the deaths with it?
• Hand in paper when finished, read article
  silently

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• List any two causes/factors for the Hartford
  Circus Fire.
• Many causes/factors lit match/cigarette,
  flammable waterproofing material, no fire
  extinguishers, narrow exits, tents nailed to
  ground, being unprepared
• What major world event was going on when the fire
  occurred?
• A World War II
• What was the 2-component mixture used to
  waterproof the circus tent?
• A parafin wax and gasoline
• Who did the public blame - who was the scapegoat
  - for the fire and the deaths with it?
• A Most people blamed the circus owners and
  performers

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Surface Tension Activities

• Obtain a dropper, piece of waxed paper, a penny
  and a cup of water.
• Place 1 drop of water in the center of the wax
  paper. Notice how it looks, write down what you
  see. Roll the drop around the paper without
  spilling. What did you notice?
• Dry off the paper when you are done, return to
  the center table.
• Place penny flat on table. Using the dropper,
  slowly add drops of water onto the penny. See how
  many you can add until the water flows off the
  penny. Record the number on your sheet.

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Write About It
Use information from the video or the article to
answer the questions below in complete sentences.

• Imagine you are a spectator (person in the
  audience) at the Hartford Circus. When you see
  the fire, what is the first thing you do. Explain
  why.
• Many people went back inside the tent after they
  had escaped. Why do you think they did this?
  Would you do the same thing, or something
  different?
• Imagine your are an investigator of the Hartford
  Circus Fire. You now know some of the
  causes/factors of the fire. What are some
  suggestions or recommendations you would give the
  circus owners to prevent future fires?