Final answer:
SiH4 is expected to have the longest bond lengths due to the size of the silicon atom. HCl is expected to have the most polar bonds because of the large electronegativity difference between hydrogen and chlorine, while SiH4 is expected to have the least polar bonds, given the smaller electronegativity difference between silicon and hydrogen.
Step-by-step explanation:
Analysis of Bond Lengths and Polarity
The question asks us to evaluate the bond lengths and electronegativity differences of four compounds: SiH4, PH3, H2Se, and HCl, using periodic trends in bond lengths and the electronegativity table in Chang. Here is the analysis based on chemical bonding concepts:
(a) The molecule expected to have the longest bonds is typically the one with the largest atoms involved. SiH4 has silicon, which is larger than the phosphorus in PH3, the selenium in H2Se, and the chlorine in HCl. Thus, SiH4 is expected to have the longest bond lengths, as bond length increases with the size of the atoms bonded.
(b) The molecule expected to have the most polar bonds is HCl. Polar bond formation is based on the electronegativity difference between the bonded atoms. Chlorine has a significantly higher electronegativity than hydrogen, resulting in a pronounced difference and, consequently, a more polar bond.
(c) The molecule expected to have the least polar bonds is SiH4. Silicon and hydrogen have less electronegativity difference compared to the other compounds listed, making SiH4 the least polar with the weakest dispersion forces among those mentioned.