Test: MCAT Physical

Electronegativity is an important concept in physical chemistry, and often used to help quantify the dipole moment of polar compounds. Polar compounds are different from those compounds that are purely nonpolar or purely ionic. An example can be seen by contrasting sodium chloride, NaCl, with an organic molecule, R-C-OH. The former is purely ionic, and the latter is polar covalent.  

When comparing more than one polar covalent molecule, we use the dipole moment value to help us determine relative strength of polarity. Dipole moment, however, is dependent on the electronegativity of the atoms making up the bond. Electronegativity is a property inherent to the atom in question, whereas dipole moment is a property of the bond between them.

For example, oxygen has an electronegativity of 3.44, and hydrogen of 2.20. In other words, oxygen more strongly attracts electrons when in a bond with hydrogen. This leads to the O-H bond having a dipole moment.

When all the dipole moments of polar bonds in a molecule are summed, the molecular dipole moment results, as per the following equation.

Dipole moment = charge * separation distance

1.

Water is commonly called the universal solvent, in part due to its relatively strong molecular dipole moment. What is true of the oxygen atom in water's O-H bonds?

The oxygen atom has two lone pairs

The oxygen atom will reversibly break its covalent bond with hydrogen in order to dissolve added solutes

The oxygen atom reduces the hydrogen atom with which it shares a bond

The oxygen atom forms the positive pole in water's dipole

The oxygen atom is sp2 hybridized

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