Lewis and VSEPR worksheet answers
1.  CS2
(a)  total valence electrons = carbon + 2*sulfur = 4  +  2*6 = 16
(b)  the Lewis dot structure will have the carbon as the central atom.
(c)  Thus, the electronic shape is linear because there are two regions of electron density.
(d)  The molecular shape is also linear since there are no lone pairs on the central atom.
CS2
CS2
CS2

2.  NF3
(a)  the total valence electrons = nitrogen + 3*fluorine = 5 + 3*7 = 26
(b)  The Lewis dot structure will have the nitrogen as the center atom.
(c)  Thus, the electronic shape is tetrahedral because there are four regions of electron density
(d)  The molecular shape is trigonal pyramidal since there is one lone pair on the central atom.
NF3
NF3
NF3
 
3.  CO32-
(a)  total valence electrons = carbon + 3*oxygen + 2*(negative charge) = 4  +  3*6 + 2= 24
(b)  the Lewis dot structure will have the carbon as the central atom.
(c)  Thus, the electronic shape is trigonal planar because there are three regions of electron density.  (This is a top view of the ion.)
(d)  The molecular shape is also trigonal planar since there are no lone pairs on the central atom.
CO3
CO3
CO3








4.  XeOF4
(a)  total valence electrons = xenon + oxygen + 4*fluorine = 8  +  6 + 4*7 = 42
(Notice that Xe has an electron configuration of [Kr]4d10 5s 25p6, but only the outer-most electrons will be used in bonding, thus only count the 5s and 5p electrons.)
(b)  the Lewis dot structure will have the xenon as the central atom.
(c)  Thus, the electronic shape is octahedral because there are six regions of electron density.
(d)  The molecular shape is square-based pyramid (square pyramidal) since there is one lone pair on the central atom.
XeOF4
XeOF4
XeOF4

5.  PCl4-
(a)  total valence electrons = phosphorous + 4*chlorine + 1*(negative charge) = 5 + 4*7 +1 = 34
(b)  the Lewis dot structure will have the phosphorous as the central atom.
(c)  Thus, the electronic shape is trigonal bipyramidal because there are five regions of electron density.
(d)  The molecular shape is see-saw (aka distorted tetrahedral) since there is one lone pair on the central atom, and the lone pair will be on an equatorial position to reduce electron-electron repulsion.

PCl4
PCl4
PCl4















6.  AsCl32-
(a)  total valence electrons = arsenic + 3*chlorine + 2*(negative charge) = 5  +  3*7 + 2 = 28
(b)  the Lewis dot structure will have the arsenic as the central atom.
(c)  Thus, the electronic shape is trigonal bipyramidal because there are five regions of electron density.
(d)  The molecular shape is t-shaped since there are two lone pairs on the central atom, and they will be in the equatorial positions to reduce electron-electron repulsion.
AsCl3
AsCl3
AsCl3#1
or, this can be turned to show the t-shape more clearly AsCl3#2
 
7.  ClF2+
(a)  total valence electrons = chlorine + 2*fluorine - 1*(positive charge) = 7  +  2*7 -1 = 20
(b)  the Lewis dot structure will have the chlorine as the central atom.
(c)  Thus, the electronic shape is tetrahedral because there are four regions of electron density.
(d)  The molecular shape is bent since there are two lone pairs on the central atom.  (Note that the bond angle will be close to ~109.5 degrees, NOT ~120 degrees like the bent structure derived from a trigonal planar structure.)
ClF2
ClF2
ClF2
or, this can be turned to show the bent structure as in
ClF2