Chemical Bonding and Molecular Shapes

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Chemical Bonding and Molecular Shapes
Chemistry 112Chapter 8

• Mr. McIsaac
• Carleton North High School

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Electron Arrangement(Energy Levels, Sublevels,
Orbitals)

• Electrons travel around the nucleus at certain
  distances, called energy levels.
• Inside each energy level, there are sublevels
  the number of sublevels is equal the number of
  the energy level
• 1st energy level has 1 sublevel (s)
• 2nd energy level has 2 sublevels (s, p)
• 3rd energy level has 3 sublevels (s, p, d)
• 4th energy level has 4 sublevels (s, p, d, f)
• 5th energy level has 5 sublevels (s, p, d, f, g)

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Electron Arrangement (cont.)

• Inside each sublevel, there are orbitals
  specific regions/areas inside the e cloud where
  individual es exist.
• An orbital may be empty, or may hold 1 or 2 es.
  Any orbital can hold a maximum of 2 es.
• An outer level (valence level) can hold a maximum
  of 8 es. So, an outer level has a maximum of 4
  orbitals.

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Electron Arrangement (cont.)

• Stated another way, an outer level has a maximum
  of 2 sublevels (s, p).
• An s sublevel has 1 orbital a p sublevel has 3
  orbitals. Total 4 orbitals 8 es (2 per
  orbital).
• Valence electrons exist in these outer 4 orbitals.

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Filling The Outer Level

• As bonded elements
• The first 4 es (1, 2, 3, 4) will
  singly/separately occupy each of the outer 4
  orbitals the 1st in the s orbital, and 2nd,
  3rd, 4th in each of the 3 p orbitals.
• The next 4 es (5, 6, 7, 8) will pair up in each
  of the outer orbitals the s, and then the 3 p
  orbitals.

• As unbonded elements (FYI we dont worry about
  it)
• The first 2 es (1 and 2) will fill the s orbital
• The next 3 es (3, 4, 5) will singly/separately
  occupy each of the 3 p orbitals.
• The next 3 es (6, 7, 8) will pair up in each of
  the 3 p orbitals.

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Lewis Electron Dot Diagrams

• In a Lewis Electron Dot Diagram for an element,
  the symbol of the element represents the nucleus
  and all the inner electrons, and the 4 sides
  around the symbol represents the 4 valence
  orbitals.

• Each of the above dot diagrams is equivalent
  any of the 4 sides is the same

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Lewis Electron Dot Diagrams

• Electrons like to exist in pairs, and single es
  bond/share with single es from other atoms.
• When two atoms share a pair of es, it is called
  a bonded pair, shared pair, or covalent bond.

• Notice that when showing dot diagrams for
  different elements forming a compound, it is
  common to use dots for one element and xs for
  the other it just makes it easier to follow.

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VSEPR TheoryAnd Predicting Molecular Shapes

• Valence Shell Electron Pair Repulsion (VSEPR)
  theory is the understanding that pairs of es
  will repel each other and move as far apart from
  each other as possible.
• Predicting molecular shapes and bond angles can
  be done by drawing dot diagrams showing the pairs
  of es (shared and unshared) around a central
  atom.

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5 Molecular ShapesFromSingle Bonds
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Double and Triple Bonds

• Adjacent atoms can share more than one pair of
  electrons.
• Try O2, N2, CH2O, CHP

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Summary Predicting Molecular Shapes

• Draw the Lewis Dot Diagram for the molecule to
  determine the number of bonding and non-bonding
  electron pairs.
• Make sure all atoms are present.
• Cannot have any single es (dots/xs) left.
• Only adjacent atoms can bond.
• Es/dots from same atom cannot pair up.
• When determining the shape of a molecule with
  multiple bonds, treat the multiple bonds as if
  they were single bonds (i.e. one bonding side or
  direction)