Which electron-dot structure, according to the formal charge rules, is the best for the bromate ion (BrO₃⁻)? 

The following generic Lewis structure is for a polyatomic oxyanion:

where X is a Period 4 element.

Three different polyatomic ions are formed when the overall charge (n) is changed to 1–, 2–, or 3–. Determine the identity and calculate the formal charge of the central atom, X, for each ion formed.

Three possible Lewis structures can be drawn for OCN^– as shown below: 

Based on formal charges, determine the most important resonance structure for OCN^–.

Aspirin (acetylsalicylic acid, C₉H₈O₄) is used to reduce pain, fever, and inflammation. Fill the structure of aspirin below with the missing hydrogens and lone pairs.

Draw the Lewis structure of PHF₂ so that the central P atom obeys the octet rule. Based on the drawing, answer the following:

The central P atom has ____ unshared pairs (lone pairs). 

The central P atom forms ____ single bonds.

The central P atom forms ____ double bonds.

A molecule is composed of 6.712% hydrogen by mass. If it is only made up of nitrogen and hydrogen, predict the lewis structure of the molecule. 

Based on their Lewis structures, rank the C—O bond lengths in CO, CO_2, and CO₃²⁻ from longest to shortest.

List the following molecules from weakest to the strongest bond between carbons: H₂NCCNH₂, H₂NCH₂CH₂NH₂, H₂NCHCHNH₂.

Count the number of the sigma bonds present in the structure of caffeine below: 

Draw the Lewis structure for periodate (IO₄^–).

Is azide ion (N₃⁻) and the triiodide ion (I₃⁻) isoelectronic?