MOLECULAR GEOMETRY TYPES MOLECULAR GEOMETRY ORGANIC MOLEC. GEOMETRY  Elmhurst College Trigonal Bipyramid    Chemistry Department Octahedral  Virtual ChemBook

	Octahedral Molecular Geometry Sulfur hexafluoride: Chime in new window An example of toctahedral molecular geometry that results from six electron pair geometry is SF6. The sulfur atom has 6 valence electrons. However this is an example where six fluoride atoms are present and the octet is expanded. The Lewis diagram is as follows: F = 7 e- x 6 = 42 e- S = 6 e- = 6 e- Total = 48 e- The fluorine atoms are as far apart as possible at nearly 90o bond angle in all directions. This is octahedral geometry. Octahedral geometry is characterized by 6 electron pairs.
	Bromine pentafluoride: Chime in new window In this example, BrF5, the Lewis diagram shows Br at the center with one lone electron pair and five fluoride atoms attached. The Lewis diagram is as follows: Br= 7 e- F = 7 e- x 5 = 35 e- Total electrons = 42 e- With five atoms and one lone pair, the electron pair geometry is octahedron. The molecular geometry is called square pyramid.
	Chlorine Trifluoride: Chime in new window In this example, ClF3, the Lewis diagram shows chlorine at the center with three fluorine atoms attached and two lone electron pairs. The Lewis diagram is as follows: Cl = 7 e- F = 7 e- x 3 = 21 e- Total electrons = 28 All fluorine atoms have an octet of electrons, and chlorine has an expanded octet. The electron pair geometry is trigonal bipyramid and the molecular geometry is T-shape. Again the axial atoms are bent slight from the 180 degree angle. Compare this with BH3 , which also has three atoms attached but no lone pair. Or ammonia, NH3, with three atoms attached and one lone pair.
	Triiodie Ion: In this example, I3-, the Lewis diagram shows I at the center with 3 lone electron pair and two other iodide atoms attached. The Lewis diagram is as follows: I = 7 e- x 3 = 21 e- -1 charge = 1 e- Total electrons = 22 e- With two atoms attached and three lone pair, the electron pair geometry is trigonal bipyramid. The molecular geometry is called linear. The triiodide ion is responsible for the blue-black color with starch. Iodine the element alone will not give the color. Iodine in mixture with iodide ions makes the triiodide ion.