Polar Bonds and Molecules

1
Polar Bonds and Molecules

• Section 16.3

2
Nonpolar vs. Polar covalent

• Nonpolar covalent- electrons are shared equally
• Same or similar electronegativities
• Polar covalent bond- bond in which electrons are
  shared unequally
• More electronegative slightly negative because
  it pulls electrons to itself
• Less electronegative slightly positive because
  it does not hold the electrons closely

3
Polarity

• Higher electronegativity greater ability to
  attract electrons
• Determining the type of bond
• Calculate the electronegativity difference
  between 2 atoms
• A range of 0.0-0.4 is nonpolar covalent.
• A range of 0.4-1.0 is moderately polar covalent.
  
• A range of 1.0 2.0 is very polar covalent.
• Over 2.0 is ionic
• Remember this is a guideline. If something has a
  metal and nonmetal it is ALWAYS ionic. If
  something has 2 nonmetals, it is ALWAYS covalent.

4
Polarity

• There is no distinct boundary between each type
  of bond
• Polar molecule- One end of the molecule is
  slightly negative and the other end is slightly
  positive
• Also called a dipole
• Polar bonds do not always create polar molecules
• It depends on the shape of the molecule

5
Intermolecular Forces

• Intermolecular forces- attractions between
  molecules
• Weaker than bonds
• Determine if something is solid, liquid, or gas
• Van der Waals forces- weakest attractive forces,
  caused by the motion of electrons
• For a split second, electrons are on one side of
  the atom or molecule, creating a brief partial
  positive and partial negative
• Forces increase with increasing number of
  electrons

6
Intermolecular Forces

• Dipole Interactions- attraction between polar
  molecules.
• Partially negative end of one molecule is
  attracted to the positive end of another molecule
  
• Hydrogen Bonds- special case of dipole
  interactions.
• Attractive forces that occur when a hydrogen
  covalently bonded to a very electronegative atom
  is attracted to an unshared electron pair of
  another electronegative atom

7
Ionic vs. Covalent Compounds

• Similarities Both can be solid, both form from
  bonding between elements
• Differences
• Ionic- Formula units, Transfer of electrons,
  Metal and Nonmetal, ALWAYS solid at room temp,
  High melting point, soluble in water, conducts
  electricity when dissolved or melted
• Covalent- Molecules, share electrons, are
  nonmetals, can be solid liquid or gas, have low
  melting points and either conduct poorly or not
  at all

8
Ionic vs. Covalent

• Ionic- have higher melting points because there
  are stronger attractions among ions than between
  molecules
• Network Solids- solids in which all of the atoms
  are covalently bonded to each other.
• Do not easily melt -may break down without
  melting
• Act like single molecules