Lewis dot structures, geometry, and intermolecular forces :)

Which of the following is the correct Lewis Dot structure for H₂O?

• Option A

• Option B

• Option C

• Option D

Answer explanation

Option C is the only dot structure that has oxygen surrounded by 8 electrons AND hydrogen by 2. Don't forget that hydrogens only need to be surrounded by 2 as our only exception.

Which of the following is the correct Lewis Dot structure for CO₂?

• Option A

• Option B

• Option C

• Option D

Answer explanation

Remembering that all elements (except H) must be surrounded by 8 electrons, the only correct choice must be B as it meets this rule for all elements.

This Lewis Dot structure represents what chemical compound?

• CHO

• C₂HO

• HCO₂

• H₂CO

Answer explanation

This compound has 2 Hydrogens, 1 Carbon, and 1 Oxygen and must be H2CO

Which element in the Lewis dot to the left would be the negative side of this compound?

• Hydrogen (H) on top

• Hydrogen (H) on bottom

• Carbon (C)

• Oxygen (O)

Answer explanation

Electronegativity increases to the top right of the periodic table, therefore Oxygen, being the highest and most right, will attract the negative charge.

Is the compound to the left polar or nonpolar?

• Polar

• Nonpolar

Answer explanation

Perfectly symmetrical on all sides, therefore nonpolar.

Which element would contain the negative charge in the Lewis dot structure to the left?

• None, nonpolar!

• Hydrogen (H) to the left

• Oxygen (O)

• Hydrogen (H) to the right

Answer explanation

Oxygen is once again the highest and most right of these compounds, and will be the most likely to have the negative charge.

Which of our molecular geometries (shapes) is the compound to the left?

• Trigonal Planar

• Tetrahedral

• Trigonal Pyramidal

• Bent

Answer explanation

The center element here is connected to four other elements. The only shape this could be with four connections is tetrahedral.

Which of our molecular geometries (shapes) is the compound to the left?

• Trigonal planar

• Tetrahedral

• Trigonal pyramidal

• Bent

Answer explanation

Our center element, P, is connected to three elements. Meaning this could be either trigonal shape, we look to the lone pair of electrons. A compound with 3 element connects and 1 pair of lone electrons can only be Trigonal pyramidal.

Which of the molecular geometries (shapes) is the compound to the left?

• Linear

• Bent

• Tetrahedral

• Trigonal Planar

Answer explanation

Our center element, S, has two elements connected, meaning this must be either linear or bent. Looking to the electrons, we have 1 lone pair on the center. This gives the compound its bent shape.

What is the strongest intermolecular force in N₂H₂?

• Hydrogen Bonding

• A firm handshake

• Dipole-dipole

• London Dispersion

Answer explanation

Drawing a Lewis Dot structure for this compound reveals that we have a N bonded to a H, meeting the hydrogen bonding requirement of N connected to a N, O, or F.