Question

What is the formal charge ( , -, or 0) of the central atom in the following molecules (assume all molecules obey the octet rule)? (Put your answers in the boxes below the molecules):

a. H₂O
b. CO₂
c. NH₃
d. CH₄

Answer 1

The formal charge of the central atom in H₂O, CO₂, NH₃, and CH₄ is 0, since the central atom in each molecule has the typical number of bonds that would lead to a neutral formal charge.

Step-by-step explanation:

The student's question pertains to the determination of the formal charge of the central atom in several molecules: H₂O, CO₂, NH₃, and CH₄. The formal charge can be calculated by taking the number of valence electrons in the free atom and subtracting the number assigned to it in the Lewis electron structure. For molecules obeying the octet rule, the formal charge will often be zero if the central atom has the typical number of bonds.

a. H₂O: Oxygen has 6 valence electrons and is bonded to 2 hydrogens with 2 lone pairs, totaling 8 electrons around it, so its formal charge is 0.

b. CO₂: Carbon has 4 valence electrons and forms double bonds with two oxygens without any lone pairs, so its formal charge is also 0.

c. NH₃: Nitrogen has 5 valence electrons, forms 3 bonds with hydrogen, and has 1 lone pair, which also leads to a formal charge of 0.

d. CH₄: Carbon has 4 valence electrons and is bonded to 4 hydrogens, resulting in a formal charge of 0, as indicated by the zero formal charge for carbon in methane (H-C°-H).