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Chapter 1: Problem 14

Which molecules are polar? For each that is polar, specify the direction of its dipole moment. (a) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) (b) \(\mathrm{HCN}\) (c) \(\mathrm{H}_{2} \mathrm{O}_{2}\)

Short Answer

Expert verified
(a) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) (b) \(\mathrm{HCN}\) (c) \(\mathrm{H}_{2} \mathrm{O}_{2}\) Answer: All three molecules are polar with the following dipole moment directions: (a) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) towards the chlorine end, (b) \(\mathrm{HCN}\) towards the nitrogen end, and (c) \(\mathrm{H}_{2} \mathrm{O}_{2}\) towards the oxygen end.

Step by step solution

01

Recall electronegativities and the concept of molecular polarity

Electronegativity is a measure of an atom's ability to attract shared electrons. Polar bonds form between atoms with significant electronegativity differences, creating a separation of charge and resulting in a partial positive charge on the less electronegative atom and a partial negative charge on the more electronegative atom. Molecular polarity occurs if these individual bond dipoles do not cancel each other, creating a net overall dipole moment.
02

Evaluate polar bonds in \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\)

In this molecule, there are two hydrogen atoms, two chlorine atoms, and one carbon atom. Comparing the electronegativities, carbon (C) has an electronegativity of 2.5, whereas chlorine (Cl) has an electronegativity of 3.0. This leads to polar bonds between carbon and chlorine. Also, carbon forms two nonpolar bonds with hydrogen (H), which has an electronegativity of 2.1.
03

Assess the molecular structure of \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\)

The carbon atom in the molecule forms four bonds in a tetrahedral geometry, with bond angles of approximately 109.5 degrees. The two carbon-chlorine bonds have the same angle with respect to the molecular center, so their dipole moments have equal magnitudes and opposite directions. This means they do not cancel out each other, resulting in a net dipole moment pointing towards the chlorine end.
04

Evaluate polar bonds in \(\mathrm{HCN}\)

In HCN, hydrogen (H) has an electronegativity of 2.1, carbon (C) has an electronegativity of 2.5, and nitrogen (N) contains an electronegativity of 3.0. This difference in electronegativity values leads to polar bonds between all atoms.
05

Assess the molecular structure of \(\mathrm{HCN}\)

HCN has a linear molecular structure, where nitrogen is more electronegative than both carbon and hydrogen. This leads to a net dipole moment pointing towards the nitrogen end.
06

Evaluate polar bonds in \(\mathrm{H}_{2} \mathrm{O}_{2}\)

In \(\mathrm{H}_{2} \mathrm{O}_{2}\), there are two hydrogen atoms and two oxygen atoms. Oxygen (O) has an electronegativity of 3.5, while hydrogen (H) has an electronegativity of 2.1. This leads to polar bonds between oxygen and hydrogen.
07

Assess the molecular structure of \(\mathrm{H}_{2} \mathrm{O}_{2}\)

\(\mathrm{H}_{2} \mathrm{O}_{2}\) has a bent molecular structure. The oxygen and hydrogen atoms all have bent angles around the central oxygen atoms. Since the electronegativity difference does not cancel out with this geometry, the molecule has a net dipole moment pointing towards the oxygen side. In conclusion, all molecules given are polar: (a) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) has a net dipole moment pointing towards the chlorine end. (b) \(\mathrm{HCN}\) has a net dipole moment pointing towards the nitrogen end. (c) \(\mathrm{H}_{2} \mathrm{O}_{2}\) has a net dipole moment pointing towards the oxygen end.

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Most popular questions from this chapter

Arrange the single covalent bonds within each set in order of increasing polarity. (a) \(\mathrm{C}-\mathrm{H}, \mathrm{O}-\mathrm{H}, \mathrm{N}-\mathrm{H}\) (b) \(\mathrm{C}-\mathrm{H}, \mathrm{B}-\mathrm{H}, \mathrm{O}-\mathrm{H}\) (c) \(\mathrm{C}-\mathrm{H}, \mathrm{C}-\mathrm{Cl}, \mathrm{C}-\mathrm{I}\) (d) \(\mathrm{C}-\mathrm{S}, \mathrm{C}-\mathrm{O}, \mathrm{C}-\mathrm{N}\) (e) \(\mathrm{C}-\mathrm{Li}, \mathrm{C}-\mathrm{B}, \mathrm{C}-\mathrm{Mg}\)

Why does fluorine, the element in the upper right corner of the Periodic Table, have the largest electronegativity of any element?

Write the ground-state electron configuration for each atom. After each atom is its atomic number in parentheses. (a) Sodium (11) (b) Magnesium (12) (c) Oxygen (8) (d) Nitrogen (7)

Phosphorus is immediately under nitrogen in the Periodic Table. Predict the molecular formula for phosphine, the compound formed by phosphorus and hydrogen. Predict the H-P-H bond angle in phosphine.

State the orbital hybridization of each highlighted atom. (a) CC (b) C=C (c) \(\mathrm{H}-\mathrm{C} \equiv \mathrm{C}-\mathrm{H}\) (d) C=O (e) O=CO (f) CCO (g) CN (h) \(\mathrm{H}-\stackrel{*}{\mathrm{O}}-\mathrm{N}=\stackrel{*}{\mathrm{O}}\) (i) \(\mathrm{CH}_{2}=\mathrm{C}=\mathrm{CH}_{2}\)
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