Chapter 3: Elements combine to form compounds

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Grade 9 Science Unit 1 Atoms, Elements, and
Compounds

• Chapter 3 Elements combine to form compounds

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Section 3.1 page 72
Compounds

• A pure substance made of two or more kinds of
  elements combined in fixed proportions.
• Chemical bonds hold them together.
• Are either ionic or covalent.

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Elements Combine to form . . .
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Covalent Compounds

• Atoms combine by SHARING electrons to form
  molecules.
• Molecules a group of atoms held together by
  sharing one or more pairs of electrons.
• Examples include carbon dioxide CO2 and water H2O.

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• Formed from non-metals ONLY.
• They do NOT conduct electricity.
• May be a solid, liquid, or gas at room
  temperature.

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Example Methane CH4
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Need to Know Molecular Compounds
Name Chemical Formula
Sugar C12H22O11
Carbon Dioxide CO2
Methane CH4
Water H2O
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Ionic Compounds

• Atoms gain or lose electrons to form ions.
• All the positive ions () attract all the
  negative ions (-) everywhere in the same crystal.
• Formed from metals and non-metals.

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• All are SOLID at room temperature.
• High melting and boiling points.
• Will conduct electricity when melted or dissolved
  in water.
• Are also called salts.

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Need to Know Ionic Compounds
Name Chemical Formula
Sodium Chloride(table salt) NaCl
Calcium carbonate CaCO3
Sodium sulfate Na2SO4
Sodium hydroxide NaOH
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SUGAR

• a-(1R,2R,3S,4S,5R)-glucopyranosyl-ß-(2S,3S,4S,5
  R)-fructofuranoside

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sodium chloride

• Crystal lattice of NaCl showing the 11 ratio of
  positive sodium ions in the green with negative
  chloride ions in the blue. Each is surrounded by
  6 ions of the opposite charge, as opposites
  attract

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Section 3.2 page 80

• Names and Formulas of Simple Compounds

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Chemical Compounds

• Every compound has a...
• Formula indicates the symbols and ratio of each
  element present in the compound.
• 2. Name indicates the elements present in the
  compound

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1. CHEMICAL FORMULAS
Symbol for Oxygen
Symbol for Carbon

• CO2

Number of C atoms, absence of number means 1 atom
present
Number of Oxygen atoms, there are 2 oxygen atoms
in this molecule
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2. CHEMICAL NAMES

• Ionic Compounds
• NaCl sodium chloride

Metal ion appears first and name remains
unchanged
Non-metal ion appears second, name looses its
ending and gains suffix ide
Even though its a name, its written in lower
case letters
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See page 81-82

• Know Names of Non-Metal Ions on Page 81 Table
  3.1
• Complete practice problems on
• pages 82

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2. CHEMICAL NAMES

• Covalent Compounds
• CF4 carbon tetrafloride

first atom name remains unchanged
second atom name looses its ending and gains
suffix ide
No prefix is used on the first atom if there is
only one atom
Prefixes are added to show the number of each atom
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See page 83

• Know Prefixes used in Naming Covalent Compounds
  on Page 83 Table 3.4
• Complete practice problems on
• pages 83

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Section 3.3 page 86

• Physical and Chemical Changes

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• PHYSICAL CHANGES
• A change in which NO NEW Substances are formed
  and no new bonds have been made.

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• Includes
• all changes in state (melting, evaporation,
  condensation, freezing)
• dissolving
• cutting
• separating
• Tend to be easy to reverse.

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• CHEMICAL CHANGES
• Produce NEW substances with NEW properties may
  or may not be noticeable.
• NEW bonds are formed while others are broken.

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Includes

• Corrosion
• Fruit ripening
• Combustion
• Cooking

• Rusting
• Reacting
• Rotting

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• Evidence of a Chemical Change
• Color change
• Heat, light, sound produced or consumed
• Gas bubbles released
• A precipitate formed
• Difficult to reverse

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• Chemical equations can be written for all
  chemical changes.
• For example the composition of water.

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• In a chemical reaction the MASS of the
  reactants the
  MASS of the products
• The elements are conserved.

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Core Lab Activity 3-3C pg. 92-3

• Observing Changes in Matter