Which Two Species are Isoelectronic Answer Key

1 of 9 1. Which two species are isoelectronic? Ba2+ and Ba Cl - and Na+ Sr2+ and Se2- Al3+ and Ar Solution or Explanation Se is in period 4; Sr is in period 5 and one atom loses 2 electrons, while the other gains 2 electrons (same electron configuration as Kr). 2. Which of the following has the largest radius? Ca2+ Cl - S2Na+ Solution or Explanation The sulfur atom gains 2 electrons, more e-e repulsions and is below chlorine on the periodic table. 3. Which of the molecules shown is polar? (Select all that apply.) (a) (b) (c) (d) 4. Which one of the following has a dipole moment? CO2 ICl Br 2 BeCl2 Solution or Explanation Both atoms are different in EN values and linear. 5. What is the shape of the phosphate ion? triangular tetrahedral linear planar Solution or Explanation AX4 class with four electron pairs. 6. Which one of the following molecules possesses a trigonal bipyramidal structure? BrF3 PF6PF5 SF4 Solution or Explanation Five electron pairs are present (AX5). 7. According to VSEPR theory, which one of the following molecules should be nonlinear? SO2 BeCl2 KrF2 CO2 C2H2 8. Which one of the following best describes the F-S-F bond angle in F2SO? 90° < angle < 109.5° 109.5° 109.5° < angle < 120° 90° Solution or Explanation 109.5 is indicated with a AX3E class, but angle is a little less due to the lone electron pair on S. 9. A molecule has the formula ML2. Atom M is the central atom and the L-M-L bond angle is 117°. What is the most likely classification of this molecule? AX2E AX2 AX2E3 AX2E2 Solution or Explanation Closest to 120 bond angle of AX2E class, with some strain a little less than 120. 10. Which of the following is the best description of the geometry of the azide ion, N3-? triangular, 120° linear, 180° angular, 120° angular, 90° Solution or Explanation Linear based on Lewis structures and thus 180 degree angle. 11. A CN22- ion has a structure that is best described as angular. linear. tetrahedral. planar. Solution or Explanation AX2 class is linear. 12. Which of the following is a non-polar molecule having one or more polar bonds? PH3 CBr4 H2 HI Solution or Explanation CBr4 is symmetrical and all the dipoles cancel out. 13. Practice Exercise 3.2 Select the Lewis structure for formic acid (HCOOH). 14. Practice Exercise 3.3 Select the Lewis structure for the nitrite ion (NO2-). 15. Practice Exercise 3.4 Give the most reasonable Lewis structure of a molecule that contains a N atom, a C atom, and an H atom. Which statements support your choice? (Select all that apply.) All atoms, except hydrogen, obey the octect rule. Formal charges are carried by some of the atoms. No formal charges are carried by any of the atoms. The three atoms have the appropriate number of valence electrons. 16. Practice Exercise 3.5 Indicate the formal charges for the nitrite ion (NO2-). (Type your answer using the format -1.) N 0 double bonded O 0 single bonded O -1 -or- 1- 17. Practice Exercise 3.6 Select the valid resonance structures for the nitrite ion (NO2-). (Select all that apply.) 18. Practice Exercise 3.7 Indicate the Lewis structure for BeF2. 19. Practice Exercise 3.11 Which of the following species has a longer bond length: F2 or F2-? F 2 20. Four atoms are arbitrarily labeled D, E, F, and G. Their electronegativities are as follows: D = 3.8, E = 3.3, F = 2.8, and G = 1.3. If the atoms of these elements form the molecules DE, DG, EG, and DF, how would you arrange these molecules in order of increasing covalent bond character? (Use the appropriate <, =, or > symbol to separate substances in the list.) DG < EG < DF < DE 21. Formal Charge Calculations (a) How many resonance structures can be drawn for the nitrate ion, NO3‾ ? one two three four (b) Consider one of the resonance structures of the nitrate ion, NO3‾. What is the formal charge of nitrogen in this polyatomic ion? +2 +1 0 -1 -2 (c) Consider one of the resonance structures of the nitrate ion, NO3‾. What is the formal charge of the oxygen atom that is doubly bonded to nitrogen? +2 +1 0 -1 -2 (d) Consider one of the resonance structures of the nitrate ion, NO3‾. What is the formal charge of one of the oxygen atoms singly-bonded to nitrogen? +2 +1 0 -1 -2 (e) What is the sum of the formal charges of all the atoms in the nitrate ion, NO3‾ ? +2 +1 0 -1 -2 22. Which of the following is the electronic configuration for a chlorine atom? 1s2 2s2 2p6 3s2 3p6 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 3s2 3p4 Solution or Explanation This is the only configuration that has precisely 17 electrons. 23. Question DetailsChang10 9.Supp.5.04. [1132224] Which of the following possesses a polar covalent bond? SO2(g) NaCl(s) Al(s) O2(g) Solution or Explanation SO2 contains two sulfur/oxygen bonds which are polar. 24. How many bond pairs (bp) and how many lone pairs (lp) should be shown in the Lewis structure for carbon monoxide? 2 bp and 3 lp 1 bp and 4 lp 4 bp and 1 lp 3 bp and 2 lp Solution or Explanation One triple bond is present, 3 bp and 2 lp. 25. Which one of the following species contains a triple bond? SO32NO2+ SO2 CN - Solution or Explanation Based on the octet rule the cyanide would show a triple bond. 26. What is the formal charge on the sulfur atom in the resonance structure of SO2 that has one single bond and one double bond? -2 -1 0 +1 Solution or Explanation 6 - 3 - 2 = +1. 27. How many equivalent resonance structures does the HCO2- ion have? 1 3 4 2 Solution or Explanation Only 2 oxygen's are present. 28. Which of the following Lewis structures best represents the cyanogen molecule, C2N2? 1. N=C=C=N 2. N 1 2 3 All of them in resonance. Solution or Explanation Based on formal charges and the octet rule, two C N and one C-C bond is the most stable. 29. The total number of bonding electrons in a molecule of formaldehyde (H2CO) is 6 4 3 18 8 30. The total number of lone pairs in NCl3 is C-C N 3. N-C C-N 9 of 9 8 10 6 13 9 31. Which of the following molecules has a higher dipole moment? molecule (a) molecule (b) 32. The CHBr3 is a slightly polar molecule. What atom substitution could be performed to make the molecule non-polar? substitute an iodine (I) for the hydrogen (H) substitute a bromine (Br) for the hydrogen (H) substitute an iodine (I) for a bromine (Br) substitute a hydrogen (H) for a bromine (Br) 11/29/2010 3:19 PM