Here are some practice molecules taken from General Chemistry Lab "Molecular Models" of the lab text.
The central atoms are described where there is an ambiguity.

CO₂

HCN

N₂O (nitrogen is the central atom)

NO₃^- (central nitrogen)

CO₃^2- (central carbon)

CH₂O (central carbon)

NO₂^- (central nitrogen)

CH₄

CHCl₃ (central carbon)

NH₃

H₂O

C₂H₆ (two central carbons)

CH₃OH (looks like this: CH₃ - O - H)

H₂O₂

C₂H₂

HCOOH (carbon has two oxygens and one hydrogen; the second hydrogen is bonded to one of the oxygens)

CH₃COOH (similar to HCOOH with CH₃ group in place of H)

C₂H₄

© 2011 Dr. R. S. Strange