Molecular Geometry
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Geometry

  1. Atoms, bonds and lone pair of electrons on a central atom repel each other.
  2. An atom bonded to four different groups, including lone pairs of electrons, is said to be tetrahedral because the four groups form a tetrahedral arrangement around the center atom, not square planar like cis and trans platinum.  LeBel proved this.
  3. The angle between two bonds to a tetrahedral atom is approximately 109.5.  Can you prove this?
  4. Ignoring unsaturations, an atom bonded to three different groups, including lone pairs of electrons, is said to be trigonal because the three different groups form a triangle arrangement around the center atom. 
  5. The angle between two bonds to a trigonal atom is approximately 120.
  6. Ignoring unsaturations, an atom bonded to two different groups, including lone pairs of electrons, is said to be linear because the two different groups form a line with the center atom. 
  7. The angle between two bonds to a linear atom is 180.

Exam question 7:  How many tetrahedral, trigonal or linear atoms are in a given structure?

Hybridization

  1. Tetrahedral atoms are called sp3 hybridized or have sp3 hybridized atomic orbitals that overlap with other orbitals with s character to make sigma bonds.
  2. 3 p's require three dimensions.
  3. Trigonal atoms are called sp2 hybridized or have sp2 hybridized atomic orbitals that overlap with other orbitals with s character to make sigma bonds.  The left over p orbital is used to make a pi bond.
  4. 2 p's require two dimensions.
  5. Linear atoms are called sp hybridized or have sp hybridized atomic orbitals that overlap with other orbitals with s character to make sigma bonds.  The left over p orbitals are used to make two pi bonds.
  6. 1 p requires one dimension.
  7. Unpaired electrons have no clout.
  8. Hydrogens only have s atomic orbitals to overlap.

Exam question  8:  How many s, sp, sp2 or sp3 hybridized atoms does a given structure have?

Bond Lengths

  1. Carbon hydrogen bonds have a length of 1.1 angstroms, .
  2. Carbon-carbon triple bonds have a length of 1.2 .
  3. Carbon-carbon double bonds have a length of 1.3 .
  4. Carbon-carbon 1.x bonds have a length of 1.4 .
  5. Carbon-carbon single bonds have a length of 1.5 .
  6. The more electronegative the atoms bonding, the shorter the bond length.
  7. Our online program is deficient in calculating bond lengths.

Exam question  9:  How many carbon-carbon bonds are 1.2, 1.3, 1.4 or 1.5 long.

 

 

 

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