Molecular Structure Models

Question 1

What is the formal charge of nitrogen atom in the ammonium ion (NH4+)?

Answer 1

+1

In the Lewis structure ammonium ion, nitrogen is singly bonded to 4 hydrogen atoms (bonding electron) with 0 lone pair (non bonding electron). Formal charge is determined by the formula:

Formal charge = (Valence electron - Bonding electron pair - Non bonding electron) = (5 - 4 - 0) = +1

Question 2

Which molecular shape does a molecule with three bonded atoms and one lone pair around the central atom adopt?

Answer 2

Trigonal pyramidal

According to the VSEPR theory, the presence of a lone pair pushes the bonded atoms downward, creating a trigonal pyramidal shape. A common example of this is ammonia (NH3).

Question 3

How do you determine the most stable resonance structure for a molecule?

Answer 3

The one with the fewest formal charges and negative charge on more electronegative atoms.

Resonance structures with more covalent bonds and minimized formal charges contribute the most to the resonance hybrid’s stability.

Question 4

What is the bond angle in a molecule with a tetrahedral geometry?

Answer 4

109.5 degrees

In a tetrahedral geometry, the electron pairs are arranged in such a way that they are as far apart as possible, resulting in bond angles of approximately 109.5 degrees. An example of compound with tetrahedral geometry would be methane (CH4)

Question 5

Which of the following does not follow the octet rule: BF3, H2O, CH4, CO2?

Answer 5

BF3

Boron in BF3 only has six electrons in its valence shell making it an exception to the octet rule.