Elements and Compounds Section 3'4

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Elements and CompoundsSection 3.4

• Chemistry

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Objectives

• Distinguish between elements and compounds.
• Describe the organization of elements on the
  periodic table.
• Explain how all compounds obey the laws of
  definite and multiple proportions.

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Elements

• What is an element?
• A pure substance that cannot be separated into
  simpler substances by physical or chemical means.
• 91 Elements occur naturally.

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http//www.physics.upenn.edu/courses/gladney/mathp
hys/subsubsection1_1_3_1.html
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Element Examples

• Copper Cu
• Oxygen O
• Gold Au

http//www.webelements.com/
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Elements

• Each element has its own name, symbol, and
  position in the periodic table of elements.
• The elements on the periodic table do not occur
  in equal amounts.

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Periodic Table of Elements

• The Periodic Table is a GREAT resource for
  information
• Dmitri Mendeleev is credited with developing the
  first rough draft of the Periodic Table of
  Elements.

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How is the Periodic Table Organized?

• The Periodic Table is set up in a grid format.
• Horizontal rows are called periods.
• Vertical rows are called groups or families.

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Why is it called the Periodic Table?

• What does periodic mean?
• A reoccurring pattern.
• The periodic table of elements organizes elements
  on the basis of their similarities that repeat
  throughout the table.
• Mendeleev noted the repeating patterns and left
  blanks in his chart for elements that were yet to
  be discovered.

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http//www.juliantrubin.com/imagesc/periodic1.jpg
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Can the Periodic Table still change?

• YES!
• The Periodic Table is a dynamic tool used by
  scientists as they continue to discover new
  elements.
• Dynamic able to change.

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Movie

• Chemistry/Periodic Table.

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Bowling for Elements

• Name the titles of the elements on the board.
• You can only progress by naming elements that
  touch each other.

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Periodic Table of Your Favorite Foods

• Your assignment is to design a periodic table of
  your favorite foods.
• It should resemble the periodic table of
  elements.
• This table should show relationships between the
  foods you like.
• Good for you ? Unhealthy
• Eating them often ? Eating them only once in a
  while.
• Etc.

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Assignment cont.

• Label periods and groups (families).
• Use some type of colored pencil, marker, or
  crayon. DO NOT USE just pencil or points will be
  deducted.
• List 30 foods.
• Organize in a pattern.
• This is due tomorrow.
• If you have questions, please ask me.

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Compounds
http//www.physics.upenn.edu/courses/gladney/mathp
hys/subsubsection1_1_3_1.html
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Compounds

• A combination of two or more different elements
  that are combined chemically.
• Many of the substances you are familiar with are
  compounds.
• Water, salt, sugar, aspirin

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Chemical Compound Symbols

• The symbols for chemical compounds are taken from
  the periodic table of elements.
• Table salt Sodium Chloride
• NaCl

http//faculty.clintoncc.suny.edu/faculty/Michael.
Gregory/files/Bio20101/Bio2010120Lectures/chemi
stry/sodium_chloride_small.jpg
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Compounds

• Compounds can be broken down into simpler
  substances by chemical means.
• Usually requires external energy.
• Electricity
• Heat

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Properties of Compounds

• A compounds properties are much different from
  its component parts.
• NaCl
• Sodium Na is a highly reactive metal that burns
  when it comes in contact with water.
• Chlorine Cl is a poisonous gas that is
  greenish-yellow.
• Salt NaCl is something we eat everyday.

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A Compounds Composition

• Law of Definite Proportions states that
  regardless of the total amount of a compound, the
  compound is always composed of the same elements
  in the same proportion by mass.

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How do we calculate a compounds composition?

• We use Percent by Mass.
• Percent by Mass (Mass of element/Mass of
  compound) x 100
• Percents need to add up to 100 when all elements
  of a compound are included.
• Example on pg 88 sucrose.

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Example Problems pg. 88

• A 78.0 g sample of an unknown compound contains
  12.4 g of hydrogen. What is the percent by mass
  of hydrogen in the compound?
• If 1.0 g of hydrogen reacts completely with 19.0
  g of fluorine, what is the percent by mass of
  hydrogen in the compound that is formed?

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Example Problems

• Two unknown compounds are tested. Compound 1
  contains 15.0 g of hydrogen and 120.0 g of
  oxygen. Compound 2 contains 2.0 g of hydrogen
  and 32.0 g of oxygen. Are the compounds the same?

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Law of Multiple Proportions

• Can compounds that are composed of the same
  elements differ from each other?
• CH4 Methane Gas
• C3H8 Propane Gas
• This law states that when different compounds are
  formed by a combination of the same elements,
  different masses of one element combine with the
  same relative mass of the other element in a
  ratio of small whole numbers.

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Assignment

• Please work in groups, and complete Section 3.4
  Assessment Questions, 24-29.
• On page 90.