CHM 129 075 Identification of Molecular Polarity
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CHM 129 075 Identification of Molecular Polarity


Using our criteria for polar and nonpolar
molecules determine whether each molecule on the slide is polar or nonpolar. Molecule A has a hydrogen atom bonded a carbon
atom which is triply bonded to nitrogen atom. Molecule B has a carbon singly bonded to three
hydrogen atoms and singly bonded to one oxygen atom which is then bonded to a hydrogen atom. Molecule C has a carbon atom singly bonded
to three hydrogen atoms and the carbon is also singly bonded to a fluorine atom. Molecule D has carbon singly bonded to four
hydrogen atoms. Pause the video to determine which molecules
are polar and which are nonpolar. Remember that the criteria for high symmetry
molecule is that there are no lone pairs on the central atom and the outer atoms are the
same element. Looking at molecule A, the carbon atom is
bonded to two different elements, hydrogen and nitrogen, so this is a polar molecule. Since nitrogen has a higher electronegativity
than carbon and hydrogen, the delta negative symbol is placed near the nitrogen and the
carbon hydrogen part of the molecule is assigned a delta positive symbol. For molecule B, the carbon atom is bonded
to two different atoms hydrogen and oxygen so it is a polar molecule. Since oxygen has a higher electronegativity
than carbon and hydrogen, the delta negative symbol is placed by the oxygen while the delta
positive symbol is placed by the part of the molecule that has carbon hydrogen bonds. Molecule C is polar since carbon is bonded
to two different elements hydrogen and fluorine. The delta negative symbol is assigned to the
fluorine atom since it is the most electronegative atom while the delta positive symbol is assigned
to the part of the molecule that has carbon hydrogen bonds. Molecule d is nonpolar carbon has no lone
pairs and it is bonded to four atoms of the same element, hydrogen. Let’s look at one more example. On the slide is the Lewis dot structure of
sulfur dioxide where sulfur is double bonded to each of the two oxygen atoms and there
is one lone pair on the sulfur atom. In sulfur trioxide the sulfur is singly bonded
to two oxygen atoms and has a double bond to the third oxygen atom. In sulfur trioxide, there are no lone pairs
on the sulfur atom. Pause the video and identify the polarity
of these two molecules Since the sulfur atom in sulfur dioxide has
a lone pair, this is a polar molecule. On the other hand, since sulfur trioxide has
a sulfur atom with no lone pairs this is a nonpolar molecule since the sulfur is bonded
to three atoms of the same element.

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