Oxygen is more electronegative than carbon and Fig. 5.18a indicates that there i
ID: 963829 • Letter: O
Question
Oxygen is more electronegative than carbon and Fig. 5.18a indicates that there is more electron density on oxigen than on the carbon in carbon monoxide. Yet the dipole moment of CO is quite small ( 0.373 x 10-30 C m; 0.112 D ) and it is known that the oxygen atom is the positive end of the dipole. Explain. Hint: Does a comparison with the isoelectronic dinitrogen molecule (Fig,5.18b ) help?
(5.4 Pa 1002 ,004 1,002 0,004 0.00 002 04 0.08 0.20 .02 d 04 DX 0,20 0,30 0.8 0.50 40 )2.0 2.0 ·4.0 0 6th 10.0 N2 Co Fig. 5.18 a) Total electron density contours for the carbon monoxide molecule. The carbon atom is on the left. (b) Total electron density contours for the dinitrogen molecule. [From Bader, R. F. W.; Bandrauk, A. D. J. Che 1653. Reproduced with permission.] m. Phys. 1968, 49Explanation / Answer
Although there is a considerable electronegative difference between C and O atom, CO has a very less dipole moment of 0.112D. This is due to the followng reason.
In order to complete octet rule C and O for a triple bond. The first two bonds are formed by the sharing of one electron each by C and O atom. This makes the O atom negatively charged and the C atom positively charged.
However the 3rd bond is formed by the complete donation of a lone pair by the O atom which is called a dative bond. This makes the donor O atom positively charged and acceptor C - atom negatively charged.
Hence in the first two bonds the polarity is towards the O atom (C ---->O) and in the third bond the polarity is towards C atom (C <----- O). These two oppositely directed polarity cancel eachother making the dipole moment very small.
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