Question

1. Use what you've learned about Lewis structures and formal charges to predict which of the following selenium-containing molecule(s) would be least likely to exist 2 In which of the folowing molecules is the carbon-oxygen bond predicted to be longest? 3 Which of the following molecules or ions does not exhibit a tetrahedral molecular geometry 4. All of the following are see-saw except 5. Consider the following species wth tetrahedral electron-pair geometries and select the species (1) SeO (2) Seo (3) SeFs (4) Sef (5) Sef (1) CO (2) HCOCH) (3) СО (4) HCO (5) (CHICO (1) CH4 (2) NH. (3) IF (4) SIC (5) BF (1) SF4 (2) IF (3) SIF (4) 10,Br- (5) Xeo,F with the smallest predicted bond angles (1) NF, (2) CCL (3) sor (4) H 0 (5) OF2 6. One resonance structure for thiocyanate ion (SCN-1) has a double bond from C to S and a double bond from C to N What the formal charge on each atom of this resonance form? (4) S o, C 2, N-3 (5) S -2, C +4, N--3 7. Which of the following require(s) a resonance hybrid for its Lewis structure (3) NO,-only (1)CO2, NO)", О) ony (2) NO', O, HO, only (4) NO,- O, only (5) None of these Сг. CO2. BF), NO, SO, XeF4 8 Which of the following molecules are polar (2) NO, XeFa only (5) NO, SO2 only (3) BFs, XeF4 only (1) Ch, CO2 only (4) CO2. NO only 9. Which of the following chlorine-containing molecules exhibits a net dipole moment (ie, which molecular is polar)? (1) BeCh (2) СС4 (3) H (4) PC, (5) SCLF2 10 Which of the following pairs of molecules is listed in order of decreasing net dipole moment (from more polar to less polar molecule) ? (1) BCI, > PC, (2) PH,>PF (3) BrFs > PFs 11. Which answer choice lists the following compounds in order of increasing molecular polarity? 12. Estimate the standard molar enthalpy of formation (AH) of CINO, expressed as kJ per mol of CINO formed, using any of the following average bond enthalpy data that may apply С-Сі. 243 klimo. N-N. 160 klimo! ; N:N, 4 1 8 kim ol ; NEN, 945 kJ/mol : 0-1, 204 kumol O-0, 498 kJ/mol C-N, 200 kJ/mol ; N-O, 607 kJ/mol; N-0, 201 kJ/mol. (1) 879 kJ/mol (2) 72 kJ/mol (3) 36 kJlmol (4) -504 kJ/mol (5) -252 kJ/mol

Answer 1

1. SeF₃ is least likely to exist.

2. H₃COCH₃ has the longest bond.

single bonds are longer than double bonds, which are longer than triple bonds.

So, C-O should be the longest.

In CO₂, H₂CO and (CH₃)₂CO, its C=O (a double bond). In CO, its a triple bond.

In H₃COCH₃, its C-O single bond. Hence it is the longest bond.

3. IF₄^- doesn't have tetrahedral geometry. It has octahedral arrangement of electrons. The molecule has square planar geometry.

4. SiF₄ has tetrahedral geometry

Si ㄇ

5. OF₂

The repulsion by lone pair electrons is greater than repulsion by bond pair electrons around the central atom. Hence, a molecule with two lone pairs, has greater repulsion and makes the bond angle shorter than in the molecule with one lone pair or no lone pair. Hence, water and OF₂ would have shorter bond angle than ammonia. Whereas, bond angle in NH₃ is shorter than that in CCl₄ or sulphate ion.

The repulsion of electrons depends on the electronegativity of the surrounding atom. Greater the electronegativity of the surrounding atom, greater the repulsion; and hence, the bond angle in OF₂ is shorter than that in H₂O.