AP CHEMISTRY 2006 SCORING GUIDELINES (Form B)

AP® CHEMISTRY 2006 SCORING GUIDELINES (Form B)

Question 6

GeCl4

SeCl4

ICl4–

ICl4+

6. The species represented above all have the same number of chlorine atoms attached to the central atom.

(a) Draw the Lewis structure (electron-dot diagram) of each of the four species. Show all valence electrons in your structures.

One point is earned for each correct structure.

(b) On the basis of the Lewis structures drawn in part (a), answer the following questions about the particular species indicated.
(i) What is the Cl – Ge – Cl bond angle in GeCl4 ?

109.5°

One point is earned for the correct angle.

(ii) Is SeCl4 polar? Explain.
Yes. The SeCl4 molecule is polar because the lone pair of nonbonding electrons in the valence shell of the selenium atom interacts with the bonding pairs of electrons, causing a spatial asymmetry of the dipole moments of the polar Se-Cl bonds. The result is a SeCl4 molecule with a net dipole moment.

One point is earned for the correct answer.

(iii) What is the hybridization of the I atom in ICl4– ?

d2sp3 or sp3d2

One point is earned for the correct hybridization.

(iv) What is the geometric shape formed by the atoms in ICl4+ ?

See-saw (or distorted tetrahedral or disphenoidal)

One point is earned for the correct shape.

© 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).
12

© 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).

© 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).

© 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).

© 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).

© 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).

AP® CHEMISTRY 2006 SCORING COMMENTARY (Form B)
Question 6 Sample: 6A Score: 7 This response earned 7 out of 8 possible points: 4 points for part (a), 1 point for part (b)(i), 1 point for part (b)(iii), and 1 point for part (b)(iv). The point was not earned in part (b)(ii) because the response indicates incorrectly that SeCl4 has no net polar moment. Sample: 6B Score: 5 Part (a) earned only 3 out of 4 possible points because the Lewis structure drawn for ICl4+ has an extra electron. The point was not earned in part (b)(i) because a bond angle of 120° is incorrect, and the point was not earned in part (b)(iv) because the geometry given is incorrect. Sample: 6C Score: 3 Only 1 point was earned in part (a) because the lone pairs of electrons are left out of the Lewis structures drawn for SeCl4 , ICl4−, and ICl4+. The point was not earned in part (b)(i) because a bond angle of 0° is incorrect. The point was earned in part (b)(ii) because the answer is consistent with the incorrect Lewis structure drawn in part (a). Part (b)(iii) is not attempted. The point was earned in part (b)(iv) because the answer is consistent with the incorrect Lewis structure drawn in part (a).
© 2006 The College Board. All rights reserved. Visit apcentral.collegeboard.com (for AP professionals) and www.collegeboard.com/apstudents (for students and parents).