Unit 2 - Learning Target 3
How many electrons are involved when two atoms in a molecule are connected by a double bond? Triple bond?
4 e- 6 e-
Although both the BF3 and NF3 molecules contain the same number of atoms, the BF3 molecule is flat whereas the NF3 molecule is trigonal pyramidal. Explain.
BF3 has 3 e- areas (3 bonded & zero lone pairs) so the molecule is flat (2-D) - trigonal planar. NF3 has 4 areas of e- (3 bonded & 1 lone pair) - the lone pair of e- givens the molecule a tetrahedral electronic shape and also makes the molecular shape be 3-D (the lone pair created the point of the pyramid)
What is the geometric structure of the water molecule? How many pairs of valence electrons are there on the oxygen atom in the water molecule? What is the approximate H-O-H bond angle in water?
Electronic structure = tetrahedral, molecular structure = bent, 2 lone pairs & 2 bonded pairs of e-, 109 ̊
What is the geometric structure of the CH4 molecule? How many pairs of valence electrons are present on the carbon atom of CH4? What are the approximate H-C-H bond angles in CH4?
Electronic structure = tetrahedral, molecular structure = tetrahedral, 0 lone pairs & 4 bonded pairs of e-, 109 ̊
What is the geometric structure of the boron triflouride molecule, BF3? How many pairs of valence electrons are present on the boron atom in BF3? What are the approximate F-B-F bond angles in BF3?
Electronic structure = trigonal planar, molecular structure = trigonal planar, 0 lone pairs & 3 bonded pairs of e-120 ̊
What is the geometric structure of the ammonia molecule? How many pairs of electrons surround the nitrogen atom in NH3? What is the approximate H-N-H bond angle in ammonia?
Electronic structure = trigonal planar, molecular structure = trigonal planar, 0 lone pairs & 3 bonded pairs of e120
Explain how the valence shell electron pair repulsion theory (VSEPR) is used to predict the arrangement of the electron pairs about the central atom
The structure around a given atom is determined by minimizing repulsion between e- pairs.
