Introduction to Chemistry

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Introduction to Chemistry
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What is Chemistry?

• Chemistry the branch of science concerned with
  the organization of matter and explaining why it
  behaves as it does
• All kinds of matter have properties to describe
  its appearance and behaviour

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Physical Properties

• Physical properties are those that can be
  observed/measured without forming a new substance
• Examples
• Color (blue, green)
• State (solid, liquid, gas)
• Odour (foul, sweet)
• Melting point (0ºC)
• Density (1 g/mL)

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Chemical Properties

• Chemical properties are those which describe how
  a substance behaves when it is reacting with
  something to form a new substance
• Example hydrogen is very flammable when reacted
  with oxygen

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• Chemical properties
• Combustibility (burns easily in oxygen)
• Reactivity (highly reactive with water, or does
  not react)
• Toxicity (highly toxic gas, non-toxic solid)

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Physical and Chemical Changes

• Changes that matter undergoes can be divided into
  two categories
• Physical changes alter the appearance or form of
  a substance, without producing a new substance
• Changes of state (ie. Ice melting) or changes of
  form (ie. Shredding paper)

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• Chemical changes result in the production of a
  totally new substance
• Example breaking down water into hydrogen and
  oxygen gases, or burning paper

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Indicators of a Chemical Change

• Chemical changes occur when a new substance
  appears, with new properties.
• The following are clues that a chemical change
  may have taken place
• Heat is produced or absorbed
• A new color appears
• A gas is produced (may be seen as bubbles in a
  liquid)
• A solid called a precipitate forms when two
  liquids are mixed
• A new odor is produced

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Classifying Matter

• There are mixtures and pure substances
• Mixtures are composed of two or more substances
  that are physically combined
• They have a variable composition
• They can be separated by physical means
• Example sand and water, salt water

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Mixtures

• There are many types of mixtures, but for our
  class, we are going to learn about
• Suspensions particles can be seen with the
  unaided eye and gravity will cause them to
  separate over time
• Example oil and vinegar
• Mechanical Mixture particles stay mixed and can
  be seen with unaided eye
• Example cereal, rocks, soil

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Mixtures

• Solutions often involve one substance being
  dissolved in another
• Particles are so small that they are best seen
  with a microscope
• Solvent substance in which the solute dissolves
  (often a liquid, like water)
• Solute the substance that dissolves in the
  solvent (often a powder)

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Mixtures

• Alloys one solid dissolved in another (they must
  be heated first, of course)
• Examples steel (iron and carbon), and bronze
  (copper and tin)

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Pure Substances

• Pure substances are composed of one substance
  only
• they have a constant composition
• Cannot be separated by physical means
• There are two types
• Elements
• Compounds

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Pure Substances

• Elements
• Cannot be broken down by physical or chemical
  means
• Composed of one type of atom
• Elements combine to form all matter
• Examples gold, aluminum, carbon, oxygen

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Pure Substance

• Compound
• Two or more elements bonded together chemically
• They cannot be broken down by physical means but
  can be broken down by chemical means
• Examples water, copper sulfate

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