Question

The formulas of several chemical substances are given in the table below. For each substance in the table, give its chemical name and predict its molecular structure.

Formula Name Molecular Structure

CO₂ __________ ___________

NH₃ __________ ___________

SO₃ __________ ___________

H₂O __________ ___________

ClO₄^- __________ ___________

Short answer

Formula	Name	Molecularstructure
${\mathrm{CO}}_2$	Carbon dioxide	Linear
${\mathrm{NH}}_3$	Ammonia	Trigonal pyramidal
${\mathrm{SO}}_3$	Sulfur trioxide	Trigonal planar
${\mathrm{H}}_2\mathrm{O}$	Water	Bent shape
${{\mathrm{ClO}}_4}^{-}$	Perchlorate ion	Tetrahedral

Step-by-step solution

– Predicting structure using VSEPR theory

The VSEPR theory helps in predicting the structure of covalent molecules. The number of bond pair and lone pairs dictates the geometry and structure of the molecule.

– Calculating the number of bond pairs and lone pairs

• $$\begin{gathered} {\mathrm{CO}}_2=4+2\times 2=8\mathrm{electrons} \\ =2\mathrm{\sigma }\mathrm{bond}\mathrm{pair}+2\mathrm{\pi }\mathrm{bond}\mathrm{pair} \end{gathered}$$

The structure of carbon dioxide is linear because 2 sigma bond pairs are present.$\mathrm{\pi }$bond pairs do not contribute to geometry.

• $$\begin{gathered} {\mathrm{NH}}_3=5+3\times 1=8\mathrm{electron}\mathrm{pairs} \\ =4\mathrm{electron}\mathrm{pairs} \\ =3\mathrm{\sigma }\mathrm{pairs}+1\mathrm{\pi }\mathrm{pairs} \end{gathered}$$

The geometry of ammonia is trigonal bipyramid.

• $$\begin{gathered} {\mathrm{SO}}_3=6+3\times 2=12\mathrm{electrons} \\ =6\mathrm{electrons}\mathrm{pairs} \\ =3\mathrm{\sigma }\mathrm{bond}\mathrm{pair}+3\mathrm{\pi }\mathrm{bond}\mathrm{pair} \end{gathered}$$

The geometry of sulphur trioxide is trigonal planar.

• $$\begin{gathered} {\mathrm{H}}_2\mathrm{O}=6+2\times 1=8\mathrm{electrons} \\ =4\mathrm{electron}\mathrm{pairs} \\ =2\mathrm{\sigma }\mathrm{bond}\mathrm{pair}+2\mathrm{lone}\mathrm{pair} \end{gathered}$$

The geometry of water is bent because of repulsion between lone pairs and bond pairs.

• $$\begin{gathered} {{\mathrm{ClO}}_4}^{-}=7+4\times 1+1=12\mathrm{electrons} \\ =6\mathrm{electron}\mathrm{pairs} \\ =4\mathrm{\sigma }\mathrm{bond}\mathrm{pair}+2\mathrm{\pi }\mathrm{bond}\mathrm{pair} \end{gathered}$$

The geometry of the chlorate ion is tetrahedral.