Q113E - Chemistry (OpenStax)

Question

Use the simulation (http://openstaxcollege.org/l/16MolecPolarity) to perform the following exercises for a real molecule. You may need to rotate the molecules in three dimensions to see certain dipoles. (a) Sketch the bond dipoles and molecular dipole (if any) for O3. Explain your observations. (b) Look at the bond dipoles for NH3. Use these dipoles to predict whether N or H is more electronegative. (c) Predict whether there should be a molecular dipole for NH3 and, if so, in which direction it will point. Check the molecular dipole box to test your hypothesis.

Step-by-Step Solution

Answer

a) Central O atom, has partial positive charge

Other two O atoms have partial negative charge (and are equally charged)

Since molecule is bent, bond moments will not cancel each other. The molecule dipole is equal to the vector sum of bond moments, and the molecule is polar.

 

b) All bond dipoles are pointed at \(N\) atom, hence, the Electronegativity of \({\rm{N}}\) is higher than the Electronegativity of \({\rm{H}}\)

 

c) The direction of a molecular dipole for \({\rm{N}}{{\rm{H}}_3}\) is shown on the sketch.

Step 1: Definition of dipole

A dipole usually refers to the separation of charges within a molecule between two covalently bonded atoms or atoms that share an ionic bond

Step 2: Sketch the bond dipoles and molecular dipole (if any) for O3

a)

For\({{\rm{O}}_3}\), we must draw the bond dipoles and molecular dipoles.

Bond moments will not cancel each other since the molecule is bent. The vector total of bond moments equals the molecule dipole, and the molecule is polar.

Therefore, partially positive charge on the central atom.

The other two atoms are somewhat charged negatively (and are equally charged)

Bond moments do not cancel each other since the molecule is bent. The vector total of bond moments equals the molecule's dipole, and the molecule is polar.

Step 3: dipoles to predict whether N or H is more electronegative

b)

Explanation,

- The O atom in the center has a partial positive charge.

- The other two O atoms are somewhat charged (and are equally charged)

Bond moments will not cancel each other since the molecule is bent. The vector total of bond moments equals the molecule dipole, and the molecule is polar.

Therefore, because all bond dipoles point toward the \(N\) atom, the Electronegativity of is \({\rm{H}}\)greater than the Electronegativity of \(N\).

 

Step 4 : Check the molecular dipole box

c) For\({\rm{N}}{{\rm{H}}_3}\), we must now anticipate the direction of a molecule dipole.
The molecular dipole will be pointed as depicted in the sketch since it has a trigonal pyramid structure and all three bond dipoles are pointing towards N Atom.

Therefore, on the sketch, the direction of a molecule dipole is \({\rm{N}}{{\rm{H}}_3}\) depicted.