Question #c3e59
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"How do covalent bonds affect physical properties?"
B. #"CH"_3"CH"_2"OH"# has eight covalent bonds.
A. #"HOCH"_2"CH"_2"OH"#
This compound has 1 #"C-C"# bond, 2 #"C-O"# bonds, 4 #"C-H"# bond, and 2 #"O-H"# bonds, for 9 covalent bonds.
B. #"CH"_3"CH"_2"OH"#
Ethanol

This compound has 1 #"C-C"# bond, 1 #"C-O"# bond, 5 #"C-H"# bonds, and 1 #"O-H"# bond, for a total of eight covalent bonds.
C. #"HOCOCOOH"#

This compound contains 1 #"C-C"# bond, 6 #"C-O"# bonds (each #"C=O"# counts as two covalent bonds), and 2 #"O-H"# bonds, for 9 covalent bonds.
D. #"HOCH"_2"COOH"#
This compound contains 1 #"C-C"# bond, 4 #"C-O"# bonds, 2 #"C-H"# bonds, and 2 #"O-H"# bonds, for 9 covalent bonds.
#B# is the correct option
We can use the following formula to determine the number of covalent bonds in a molecule.
#"Number of covalent bonds"=(x-y)/2#
where #x# is the total number of electrons required to fulfil the octet for atom other than hydrogen atom and doublet for hydrogen atom.
and #y# is the total number of valence electrons.
A) For compound #HOCH_2CH_2OH#
which consists of 2C ,2O and 6H ,we have
#x=2*8+2*8+6*2=44#
#y=2*4+2*6+6*1=26#
So #"Number of covalent bonds"=(x-y)/2=(44-26)/2=9#
B) For compound #CH_3CH_2OH#
which consists of 2C ,1O and 6H ,we have
#x=2*8+1*8+6*2=36#
#y=2*4+1*6+6*1=20#
So #"Number of covalent bonds"=(x-y)/2=(36-20)/2=8#
C) For compound #HOCOCOOH#
which consists of 2C ,4O and 2H ,we have
#x=2*8+4*8+2*2=52#
#y=2*4+4*6+2*1=34#
So #"Number of covalent bonds"=(x-y)/2=(52-34)/2=9#
D) For compound #HOCH_2COOH#
which consists of 2C ,3O and 4H ,we have
#x=2*8+3*8+4*2=48#
#y=2*4+3*6+4*1=30#
So #"Number of covalent bonds"=(x-y)/2=(48-30)/2=9#