Chapter 8

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Chapter 8Covalent Bonding
Ball-and-stick model
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Section 8.1Molecular Compounds

• OBJECTIVES
• Distinguish between the melting points and
  boiling points of molecular compounds and ionic
  compounds.

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Section 8.1Molecular Compounds

• OBJECTIVES
• Describe the information provided by a molecular
  formula.

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Bonds are

• Forces that hold groups of atoms together and
  make them function as a unit. Two types

1. Ionic bonds transfer of electrons (gained or
   lost makes formula unit)
2. Covalent bonds sharing of electrons. The
   resulting particle is called a molecule

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Covalent Bonds

• The word covalent is a combination of the prefix
  co- (from Latin com, meaning with or
  together), and the verb valere, meaning to be
  strong.
• Two electrons shared together have the strength
  to hold two atoms together in a bond.

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Molecules

• Many elements found in nature are in the form of
  molecules
• a neutral group of atoms joined together by
  covalent bonds.
• For example, air contains oxygen molecules,
  consisting of two oxygen atoms joined covalently
• Called a diatomic molecule (O2)

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How does H2 form?

• The nuclei repel each other, since they both have
  a positive charge (like charges repel).

(diatomic hydrogen molecule)
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How does H2 form?

• But, the nuclei are attracted to the electrons
• They share the electrons, and this is called a
  covalent bond, and involves only NONMETALS!

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Covalent bonds

• Nonmetals hold on to their valence electrons.
• They cant give away electrons to bond.
• But still want noble gas configuration.
• Get it by sharing valence electrons with each
  other covalent bonding
• By sharing, both atoms get to count the electrons
  toward a noble gas configuration.

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Covalent bonding

• Fluorine has seven valence electrons (but would
  like to have 8)

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Covalent bonding

• Fluorine has seven valence electrons
• A second atom also has seven

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Covalent bonding

• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons

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Covalent bonding

• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons

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Covalent bonding

• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons

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Covalent bonding

• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons

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Covalent bonding

• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons

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Covalent bonding

• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons
• both end with full orbitals

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Covalent bonding

• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons
• both end with full orbitals

F
F
8 Valence electrons
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Covalent bonding

• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons
• both end with full orbitals

F
F
8 Valence electrons
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Molecular Compounds

• Compounds that are bonded covalently (like in
  water, or carbon dioxide) are called molecular
  compounds
• Molecular compounds tend to have relatively lower
  melting and boiling points than ionic compounds
  this is not as strong a bond as ionic

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Molecular Compounds

• Thus, molecular compounds tend to be gases or
  liquids at room temperature
• Ionic compounds were solids
• A molecular compound has a molecular formula
• Shows how many atoms of each element a molecule
  contains

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Molecular Compounds

• The formula for water is written as H2O
• The subscript 2 behind hydrogen means there are
  2 atoms of hydrogen if there is only one atom,
  the subscript 1 is omitted
• Molecular formulas do not tell any information
  about the structure (the arrangement of the
  various atoms).

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- Page 215
3. The ball and stick model is the BEST, because
it shows a 3-dimensional arrangement.
These are some of the different ways to represent
ammonia
1. The molecular formula shows how many atoms of
each element are present
2. The structural formula ALSO shows the
arrangement of these atoms!