exam 2 - Version 005 Exam 2 mcdevitt (52365) This print-out...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Version 005 – Exam 2 – mcdevitt – (52365) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. You are responsible For answering 25 ques- tions correctly. There are two extra credit questions. 001 10.0 points Which oF the Following is the correct Lewis Formula For carbon dioxide (CO 2 )? 1. b b b b b b b b b b b b O C O 2. b b b b b b b b b b b b b b b b b b O C O 3. b b b b b b b b b b b b b b b b O C O 4. O b b b b b b b b b b b b C O 5. b b b b b b b b O C O correct 6. b b b b O C O 7. b b b b b b b b b b O C O 8. b b b b b b b b b b b b b b O C O 9. O b b b b b b b b C O 10. O b b C O Explanation: C contributes 4 valence e and each O con- tributes 6 valence e For a total oF 16 e . The Lewis Formula For carbon dioxide (CO 2 ) is b b b b b b b b O C O 002 10.0 points An ionic bond is Formed when electrons are 1. split. 2. transFerred. correct 3. destroyed. 4. shared. Explanation: 003 10.0 points Which oF the Following molecules is polar? 1. CH 4 2. NH 3 correct 3. 4 4. H 2 5. BH 3 Explanation: CH 4 and C± 4 are both tetrahedral and sym- metric. Polar bonds will cancel. H 2 is a di- atomic molecule and is not polar. Both Hs have the same EN and thereFore there is no ΔEN and the bond is not polar. BH 3 is trigo- nal planar and symmetric. There are no lone pairs because B is an exception to the octet rule. The 3 B H bonds cancel each other. NH 3 has 3 polar N H bonds and 1 lone pair on N. NH 3 has tetrahedral electronic geome- try and trigonal pyramidal geometry. The molecule is not symmetric, the N H bonds polarities do not cancel, and it is thereFore a polar molecule. 004 10.0 points How many polar covalent bonds are in NH 3 ? 1. 4 2. 3 correct 3. 1 4. None oF these 5. 2 Explanation: To draw the dot structure For NH 3 we must frst calculate the number oF valence electrons
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Version 005 – Exam 2 – mcdevitt – (52365) 2 available from the atoms. A = 5 × 1 (N atom) + 1 × 3 (H atoms) = 8 e Hydrogen can form only one bond, so nitro- gen must be the central atom. We place the other atoms symmetrically around the nitro- gen atom. The correct dot structure for the molecule should show a complete octet (8 electrons) around the nitrogen atom and two electrons around each hydrogen atom, a total of 8 va- lence electrons for the entire structure: N ·· H H H There are 3 bonds in the structure. Nitrogen-hydrogen bonds, bonds between two non-metal atoms, will be covalent. Since nitrogen and hydrogen have diFerent elec- tronegativities, these bonds will be polar. (If using the
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/16/2009 for the course CH 52365 taught by Professor Mcdevitt during the Spring '09 term at University of Texas at Austin.

Page1 / 7

exam 2 - Version 005 Exam 2 mcdevitt (52365) This print-out...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online