VSEPR Theory and Polarity

What does VSEPR stand for?

• Very Sad Engineering Process Report

• Valence Electron Shell Pair Repulsion

• Victoria's Secret's Excessive Public Relations

• Valence Shell Electron Pair Repulsion

Answer explanation

VSEPR Theory: Valence Shell Electron Pair Repulsion Theory.

Dictates the 3D shape of a molecule.

Sometimes written as "VESPR."

The oxygen atom in water has ___ lone pairs.

Answer explanation

The oxygen atom has 2 lone pairs on it.

Draw the Lewis dot structure of HCl.

Answer explanation

The Lewis dot structure for HCl is a hydrogen atom single bonded to a chlorine atom. The chlorine atom should have three lone pairs around it.

What is the molecular shape of HCN?

• Linear

• Trigonal Planar

• Bent

Answer explanation

The Lewis structure for HCN shows us that HCN has two bond sites and no lone pairs on the central atom (Carbon). Therefore, the molecular shape is linear.

What is the electron geometry of water?

• Linear

• Trigonal Planar

• Bent

• Tetrahedral

Answer explanation

Electron Geometry accounts for all the electron groups on a molecule (bonds and lone pairs).

While H2O has a bent molecular shape, the electron geometry is a tetrahedral (2 lone pairs + 2 bond sites).

What is the molecular shape of this molecule?

• Tetrahedral

• Trigonal Pyramidal

• Square Pyramidal

• Trigonal Planar

Answer explanation

NCl3 has a lone pair on the central atom. This lone pair will push the bond sites away, creating a trigonal pyramidal 3D shape.

What is the best description for this molecule?

• Non-Polar, Tetrahedral

• Non-Polar, Square Pyramidal

• Polar, Square Pyramidal

• Non-Polar, Trigonal Pyramidal

• Polar, Tetrahedral

Answer explanation

CHF3 is a polar molecule because the pull from a hydrogen atom is different enough from the pull of a Fluorine atom that a dipole is created.

CHF3 is a has four bonding sites and no lone pairs. Therefore, it has a tetrahedral molecular shape.

Which is the best explanation for why this molecule is polar?

• The phosphorus atom is more electronegative than the chlorine atoms.

• The molecular shape is asymmetric.

• The molecular shape is asymmetric and the chlorine atoms are more electronegative than the phosphorus atoms.

• The chlorine atoms are more electronegative than the phosphorus atom.

Answer explanation

PCl3 is an asymmetric molecule with a trigonal pyramidal molecular geometry.

The chlorine atoms are also more electronegative than the phosphorus atom, creating a dipole towards them.

Both these properties create a net dipole (shown in blue), making the molecule polar.

This molecule is ___ (non-polar/polar).

Answer explanation

The alcohol group (-OH) on the end of the molecule will create a polar covalent bond with the carbon atoms.

This bond will have a dipole moment towards the oxygen atom making the molecule polar.

What is the electron geometry around the nitrogen atom in CH3NH2?

• Tetrahedral

• Trigonal Pyramidal

• Trigonal Planar

• Bent

Answer explanation

The nitrogen atom in CH3NH2 has three bonding sites and a lone pair.

This would give the nitrogen atom a tetrahedral electron geometry.