Draw Lewis structures for the following species in the boxes provided and use them to answer the questions below: What is the electron pair geometry for SiS_(2) ? a. linear b. trigonal planar c. tetrahedral d. trigonal bipyramidal e. octahedral What is the molecular shape of SiS_(2) ? a. tetrahedral b. bent c. trigonal pyramidal d. linear e. trigonal planar The approximate S-Si-S bond angle(s) in SiS_(2) is/are: a. 90deg b. 109.5deg c. 120deg d. 90deg and 120deg e. 180deg What is the electron pair geometry for PCl_(5) ? a. linear b. trigonal planar c. tetrahedral d. trigonal bipyramidal e. octahedral What is the molecular shape of PCl_(5) ? a. trigonal bipyramidal b. bent c. tetrahedral d. T-shape e. trigonal planar The approximate Br-P-Br bond angle(s) in PCl_(5) is/are: a. 90deg b. 109.5deg c. 120deg d. 90deg and 120 e. 180deg The SiS_(2) molecule is and the PCl_(5) molecule is b. polar, polar b. nonpolar, polar c. polar, nonpolar d. nonpolar, nonpolar Draw Lewis structures for the following species in the boxes provided and use them to answer the questions below SiS2 PBrs What is the electron pair geometry for SiS? a. linear d. trigonal bipyramidal b. trigonal planar e.octahedral c.tetrahedral What is the molecular shape of SiS? a.tetrahedral d. linear b.bent e.trigonal planar c. trigonal pyramidal The approximate S-Si-S bond angle(s) in SiSis/are a.90 b. 109.5 c.120 d. 90 and 120 e. 180 What is the electron pair geometry for PCIs? a. linear d.trigonal bipyramidal b. trigonal planar e.octahedral c. tetrahedral What is the molecular shape of PCls? a. trigonal bipyramidal d.T-shape b. bent e. trigonal planar c. tetrahedral The approximate Br-P-Br bond angle(s) in PCls is/are: a. 90 b.109.5 c.120 d.90 and 120 e. 180 The SiS molecule is and the PCls molecule is b. polar, polar c. polar, nonpolar b. nonpolar, polar d. nonpolar, nonpolar
Correct Answers:
SiS₂:
- Electron pair geometry: a. linear
- Molecular shape: d. linear
- Approximate S–Si–S bond angle: e. 180°
PCl₅:
- Electron pair geometry: d. trigonal bipyramidal
- Molecular shape: a. trigonal bipyramidal
- Approximate Cl–P–Cl bond angles: d. 90° and 120°
Polarity:
- SiS₂ molecule is: d. nonpolar
- PCl₅ molecule is: d. nonpolar
Explanation:
To understand the geometry and polarity of molecules, Lewis structures must be drawn first. For SiS₂, silicon is the central atom, forming two double bonds with sulfur atoms. Since there are no lone pairs on silicon, and the molecule consists of only two regions of electron density (two bonding groups), the electron pair geometry is linear. Because the structure is symmetric and the same atoms are bonded to the central atom, the dipoles cancel, making SiS₂ nonpolar. The bond angle in a linear molecule is approximately 180°.
In the case of PCl₅, phosphorus has five valence electrons and forms five single bonds with five chlorine atoms. The electron pair geometry is trigonal bipyramidal, consisting of three equatorial positions with 120° angles and two axial positions with 90° angles to the equatorial plane. Since the geometry is symmetric and all bonded atoms are identical, the bond dipoles cancel out, making PCl₅ nonpolar. Therefore, Cl–P–Cl bond angles are both 90° and 120°.
Understanding molecular geometry helps in predicting the behavior and reactivity of substances. For instance, linear molecules like SiS₂ are more likely to pack closely in solid form, while the trigonal bipyramidal shape of PCl₅ makes it more space-filling and reactive, especially as it can undergo axial and equatorial substitutions due to its geometry.
