6.8 Shapes of Molecules

6.8 Shapes of Molecules

  • Predict whether the bonds are nonpolar d+ or negative end d-.
    • An arrow is needed to show the ionic, polar, and covalent: dipoles.
  • Lewis structures can be used to predict three-dimensional shapes.
  • Our sense of taste and smell is influenced by the shape of the molecule.
    • The three-dimensional shape of a molecule is determined by drawing its Lewis structure and counting the number of electron groups around the central atom.
    • The shape of the central atom can be determined from the number of atoms bonding to it.
  • There are two double bonds attached to the central atom in the Lewis structure for CO2.
  • The central atom C is attached to two H atoms by single bonds and to the O atom by a double bond in the Lewis structure.
  • The shape and the electron-group geometry have the same name when the central atom has the same number of electron groups.
  • There are three electron groups around the central S atom in the Lewis structure, a single bond to an O atom, a double bond to another O atom, and a lone pair of electrons.
    • Three electron groups have minimal repulsion when they form a geometry.
    • One of the electron groups has only one pair of electrons.
    • The shape and electron-group geometry of the central atom have different names.
  • The central C atom is attached to four H atoms in a molecule of methane.
    • From the Lewis structure, you might think that CH4 is 90 degree bond angles.
  • The two bonds connecting carbon to hydrogen are in the plane of the paper.
    • The wedge and dash represent carbon-to-hydrogen bonds going into the page away from us.
  • We can look at the four electron groups of the molecule and see if there are any lone pairs of electrons.
    • The central atom has two or three atoms.
  • Four electron groups have a geometry.
  • One of the electron groups is a pair of electrons.
    • The shape of NH in a PH 3 is determined by the three H atoms and the central N atom.
  • H bond is leaving us.
  • The Lewis structure for water has four electron groups which have minimal repulsion.
    • There are two pairs of electrons in H2O.
  • The bond angles may be different.
  • The shape of the molecule is predicted using the VSEPR theory.
  • The Lewis structure can be drawn.