Covalent bonds bond dipole moments

In a molecule with only one covalent bond, the dipole moment of the molecule is identical to the dipole moment of the bond. For example, the dipole moment of hydrogen chloride (HCl) is 1.1 D because the dipole moment of the single H—Cl bond is LID. The dipole moment of a molecule with more than one covalent bond depends on the dipole moments of all the bonds in the molecule and the geometry of the molecule. We will examine the dipole moments of molecules with more than one covalent bond in Section 1.15 after you learn about the geometry of molecules. 

In Section 1.3, we saw that for molecules with one covalent bond, the dipole moment of the bond is identical to the dipole moment of the molecule. For molecules that have more than one covalent bond, the geometry of the molecule must be taken into account because both the magnitude and the direction of the individual bond dipole moments (the vector sum) determine the overall dipole moment of the molecule. Symmetrical molecules, therefore, have no dipole moment. For example, let s look at the dipole moment of carbon dioxide (CO2). Because the carbon atom is bonded to two atoms, it uses sp orbitals to form the C—O a bonds. The remaining two p orbitals on carbon form the two C—O tt bonds. The individual carbon-oxygen bond dipole moments cancel each other— because sp orbitals form a bond angle of 180°—giving carbon dioxide a dipole moment of zero D. Another symmetrical molecule is carbon tetrachloride (CCI4). The four atoms bonded to the sp hybridized carbon atom are identical and project symmetrically out from the carbon atom. Thus, as with CO2, the symmetry of the molecule causes the bond dipole moments to cancel. Methane also has no dipole moment. 

Not all molecules containing polar covalent bonds have dipole moments. Many do, including all those shown in Problem 1.4 but consider carbon dioxide (CO2), a linear molecule of the structure O C O (the double lines represent double bonds in which the carbon atom shares two pairs of electrons with each oxygen atom). Because oxygen is more electronegative than carbon (Table 1.8), both bonds... 

Bond Dipole Moments (Debye) for Some Common Covalent Bonds... 

Discnss this comparison in terms of mixed ionic and covalent character of the H—Cl bond. The dipole moment can also be discussed in terms of the difference in electronegativity between the H and Cl atoms. ... 

I Table 1.7 Average Bond Dipole Moments of Selected Covalent Bonds... 

Bond dipole moment (fi) (Section 1.2B) A measure of the polarity of a covalent bond. The product of the charge on either atom of a polar bond times the distance between the atoms. 

Keywords Bond order Dipole moment Force constant General covalence Ionization radius Golden ratio... 

In addition to the in situ electronegativity of atom A, EIa, there is also the question of in situ bond polarity across the bond AB in a molecule. At first, one would expect this to be IEa — IEb, but bond polarity is the ionic component (bond dipole moment) of the AB bond, and thus the covalent component must be subtracted out. So the bond polarity index, BPIab, must be defined as... 

Many covalent bonds have dipoles and dipole moments within dmg molecules are important for their interaction with the biomolecules within cells which transmit the dmg s action. The larger the dipole, the stronger the dipolar interaction with proteins and receptors within the cell. In addition, the strength of the dipole moment gives an indication of how likely the dmg is to be degraded by reactants with an affinity for positive or negative charge. As indicated above, in most cases dmg action is not based on covalent bond formation. There... 

The unequal distribution of charge produced when elements of different electronegativities combine causes a polarity of the covalent bond joining them and, unless this polarity is balanced by an equal and opposite polarity, the molecule will be a dipole and have a dipole moment (for example, a hydrogen halide). Carbon tetrachloride is one of a relatively few examples in which a strong polarity does not result in a molecular dipole. It has a tetrahedral configuration... 

Carbon-oxygen and carbon-halogen bonds are polar covalent bonds and carbon bears a partial positive charge in alcohols ( " C—0 ) and in alkyl halides ( " C—X ) Alcohols and alkyl halides are polar molecules The dipole moments of methanol and chloromethane are very similar to each other and to water... 

The unequal distribution of electron density in covalent bonds produces a bond dipole, the magnitude of which is expressed by the dipole moment, having the units of charge times distance. Bonds with significant bond dipoles are described as being polar. The bond and group dipole moments of some typical substituents are shown in Table 1.7. 

Dipole moment (n ), 38 halomethanes, 335 polar covalent bonds and, 38-39 table of, 39... 

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