Chap 4 Forces Between Particles

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Chap 4Forces Between Particles
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LEWIS dot STRUCTURESValence electrons
represented by dots arranged around the elemental
symbolThey help us understand chemical
properties reactivity
What might the Lewis dot structure be for Ca ?
How about Br ? Discuss with your group
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The Octet Rule
Atoms will gain or lose sufficient electrons to
achieve an outer electron arrangement identical
to that of a noble gas.
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• Naming Binary Ionic Compounds
• name metal name stem of nonmetal name -ide

Lets Practice How would you name CaCl2, Na2S,
KBr?
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• Covalent Bonding
• The octet rule is satisfied when atoms share
  valence electrons. The shared electrons are
  counted in the octet of each atom that shares
  them
• Why do atoms do this ? Discuss
• Lets build hydrogen gas and the water molecule!

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Drawing Lewis StructuresLets Practice SO3
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• Polyatomic Ions
• Covalently-bonded groups of atoms that carry a
  net electrical charge.
• Lewis structures Lets try hydroxide and
  carbonate
• SHAPES OF MOLECULES AND POLYATOMIC IONS
• Most molecules and polyatomic ions are not flat
  two- dimensional objects. Most have distinct
  three-dimensional shapes. StructureFunction
  relationships

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Predicting Molecular Shape VSEPR

• The shapes of molecules or polyatomic ions can be
  predicted using a theory called the valence-shell
  electron repulsion theory, or VSEPR theory
• Electron pairs in the valence shell of an atom
  repel each other, and get as far away from each
  other as possible around the central atom.
• What angles might you expect for SO3? Discuss

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Arrangement of electron pairs or bonded groups
What angles are represented in these structures?
Discuss
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VSEPR--Practice
Lets draw methane, ammonia, water, and carbon
dioxide. NOW,lets predict the angles
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Bond Polarity
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Molecular Polarity
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More fun with naming
BINARY COVALENT COMPOUNDS SO2 name sulfur
di- ox -ide sulfur dioxide XeF6 name
xenon hexa- fluor -ide xenon
hexafluoride H2O name di- hydrogen mono-
ox -ide dihydrogen monoxide (also known
as water). Note, the final o of mono- was
dropped for ease of pronunciation
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Other Intermolecular Forces see handout

• The attractive forces between molecules are
  called intermolecular forces. There are three
  types
• Dipole-Dipole forces
• London Dispersion forces
• Hydrogen Bonding
• Often, there is more than one type of force
  present

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Dipole-Dipole Forces

• Electrostatic interaction of two polar molecules
• Strength of intermolecular forces increase with
  increasing polarity

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London Dispersion Forces
Increase in strength quickly with size
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London Dispersion Forces
Can you explain the boiling point data below?
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The Hydrogen Bond
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The Hydrogen BondWhat is it? How does it work?

• A special intermolecular attraction between the H
  in a polar bond (H-F, H-O or H-N) and an unshared
  electron pair on a nearby electronegative ion or
  atom (F, O or N)
• Hydrogen bonds (4 to 25 kJ/mol) are weaker than
  covalent bonds but stronger than most
  dipole-dipole or dispersion forces.

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Intermolecular forces hold you together!