Solutions

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Topic 6.6

• Solutions

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• Solutions form when a solute dissolves in a
  solvent.
• Not all substances can dissolve in one another.
• We can use information about type of bonding and
  molecular shape to predict whether one substance
  is capable of dissolving in another.

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General Rule for solubility

• Like Dissolves Like
• refers to similarities in intermolecular forces

4
Intermolecular forces (between molecules)

• are the forces which attract one molecule to the
  next.
• These forces are different in different types of
  molecules.

5
Ionic compounds

• have electrostatic forces caused by oppositely
  charged ions.
• The larger the charge, the stronger the force.

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Ionic compounds

• Weaker attraction Stronger attraction

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Covalent compounds

• Covalent compounds have a variety of
  intermolecular forces that are determined by
  their molecular shapes and polarity.
• Polar molecules
• Nonpolar molecules

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Polar Molecules

• Polar molecules have uneven distribution of
  electrons (charge) across the molecule making one
  side more negative and one side more positive.
  The molecule itself remains neutral (has no
  charge) but behaves like a small magnet.
• 
  _
• HF (polar)

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HF (Polar molecule)

• Fluorine is more electronegative than hydrogen so
  the
• bonding electrons shift toward fluorine. This
  makes the hydrogen end slightly positive and the
  fluorine end slightly negative.

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Nonpolar molecules

• Nonpolar molecules have an even distribution of
  electrons (charge) across the molecule. Their
  strength of attraction is due mainly to their
  mass and are called Van der Waals forces. There
  are no significant charges or magnetic forces in
  these molecules.

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Methane, CH4 (nonpolar)

• Carbon is more electronegative than hydrogen so
  the bonding electrons shift toward carbon.
  Because all four bonds are the same and the
  electrons are shifting toward the center, there
  is an even distribution of electrons and no
  polarity.

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When mixing substances together

• . Like dissolves like, means that if their
  intermolecular forces are similar they will
  dissolve, if they are not similar then they will
  not dissolve.
• Polar dissolves polar.
• Nonpolar dissolves nonpolar
• Polar dissolves ionic