Chemistry 200: General Chemistry I - Lecture

Transcription

1 Name Date Chemistry 200: General Chemistry I - Lecture Exam #2, 100 Points Total Form: A Read all directions carefully. Answers not conforming to the directions will be marked as incorrect! Section 1: Matching (10 points) Match the following concepts with the appropriate definitions or examples listed below. Make selections such that each term has its best possible match. Indicate your choices by marking your Scantron sheet (1-10) with the appropriate two-letter code. covalent compound σ bond O=C=O angle distortion oxoanion higher order bond molecular orbital theory δ + /δ pi bond polyatomic ion AC. held together by e- attractions to nuclei CD. arises from side-to-side orbital overlap DE. atomic orbitals are combined to form molecular orbitals AB. structural formula CE. bonding e- s lie on internuclear axis AE. e.g. NH + 4 BC. when two atoms share more than 2 electrons BD. delta notation for polar bonds AD. polyatomic ion containing oxygen BE. deviation from optimum bond angles 1

2 Section 2: Multiple Choice (40 points) Choose the term or phrase that best completes the sentence or answers the question. Indicate your selection by marking the appropriate letter on your Scantron sheet. 11. Bond energies apply to. metallic alloys ionic molecules covalent molecules (d) nonmetals 12. How many valence electrons are represented in the Lewis electron-dot structure for SO 2? (d) According to molecular orbital theory, how does a diamagnetic compound form from two paramagnetic atoms? occupancy of molecular orbitals is different than occupancy of atomic orbitals hybridization of the electronegativity difference between the atoms (d) None of these 14. Which of the following CANNOT violate the octet rule? (d) H free radicals O P 2

3 15. In SeCl 4, selenium is hybridized. sp 3 sp 3 d sp 3 d 2 (d) see-saw 16. In the trigonal bipyramidal-based electron geometries, electron lone pairs always go into the positions first. axial equatorial opposite (d) tetrahedral 17. The hybridization of the central atom in bromine trifluoride is. sp 2 sp 3 sp 3 d (d) sp 3 d When bonded to another atom, which of these elements would display the highest electronegativity? oxygen iodine cesium (d) lithium 19. The formal charge of nitrogen in nitrogen monoxide is (d) 1+ 3

4 20. Which of the following has the most oxygen atoms? (d) ammonium periodate sulfite carbonate 21. If a carbon atom is sp hybridized, it can form at most σ bond(s) (d) A compound is found to consist of 34.9% sodium, 16.4% boron, and 48.6% oxygen. What is its simplest formula? NaBO 2 NaBO 3 Na 2 B 4 O 7 (d) Na 3 BO C 3 H 6 O is the empirical formula of. C 4 H 5 O 2 H-C=O C 6 H 12 O 6 (d) C 15 H 30 O What mass of carbon is present in molecules of sucrose (C 12 H 22 O 11, MW = 342 g/mole)? (d) g g g g 4

5 25. A 4.08 g sample of a compound of nitrogen and oxygen contains 3.02 g of oxygen. What is the empirical formula? NO NO 2 N 2 O (d) N 2 O When atoms form bonds, they do so to. get an octet fill empty orbitals increase KE (d) lower PE 27. When one s and three p orbitals are hybridized, hybrid orbitals form (d) Which of the following compounds contains the greatest percentage of nitrogen? C 6 H 3 N 3 O 7 (MW = 229 g/mole) CH 4 N 2 O (MW = 60.1 g/mole) LiNH 2 (MW = 23.0 g/mole) (d) Pb(N 3 ) 2 (MW = 291 g/mole) 29. Valence bond theory is based on the central idea that. (d) covalent bonds result from orbital overlap electrons belong to the entire molecule valence electrons are more important than core electrons valence bonds want to be ionic 5

6 30. Which of the following contains a polar covalent bond? Ni/Cu alloy NO FeS (d) F 2 6

7 Section 3: Long Answer (10 points each) points. Draw the complete molecular orbital diagram for N 2 2 (from the combination of two N ions). 2 points. Calculate the bond order of this diatomic anion. 2 points. Write the molecular orbital electron configuration. (d) 1 point. Is this diatomic anion paramagnetic or diamagnetic? 7

8 32. Complete the table below with the correct formula or name for the indicated compounds. Formula Name Sc 2 (SO 4 ) 3 8H 2 O Cl 2 O Ca(HCO 3 ) 2 Mg 2 C niobium(iii) oxide carbon tetrabromide calcium nitrate iron(iii) cyanide 8

9 33. This question deals with the structure and properties of ClF points. Draw the Lewis structure. 3 points. Draw the correct molecular geometry (using proper perspective). 1 point. What is the name of the molecular geometry shape? (d) 1 point. What is the name of the electronic geometry from which the shape derives? (e) 2 points. What is the hybridization of the central atom? 9

10 34. A compound containing only carbon, hydrogen, and nitrogen is being analyzed via combustion analysis. 8 points. If a g sample of this compound leads to the recovery of g CO 2 and g of H 2 O, what is the empirical formula of the compound? 2 points. If the molar mass of the compound is g/mole, what is its molecular formula? 10

11 35. Write the bond type and the orbitals that are overlapping to form the four specified bonds in the molecule below (two of the bonds are described by the same type of overlap scheme). 11

12 Answer Key for Exam A Section 1: Matching (10 points) (1) covalent compound (5) σ bond (4) O=C=O (10) angle distortion (9) oxoanion (7) higher order bond (3) molecular orbital theory (8) δ + /δ (2) pi bond (6) polyatomic ion AC. held together by e- attractions to nuclei CD. arises from side-to-side orbital overlap DE. atomic orbitals are combined to form molecular orbitals AB. structural formula CE. bonding e- s lie on internuclear axis AE. e.g. NH + 4 BC. when two atoms share more than 2 electrons BD. delta notation for polar bonds AD. polyatomic ion containing oxygen BE. deviation from optimum bond angles 1

13 Section 2: Multiple Choice (40 points) (d) (d) 26. (d) 27. (d)

14 Section 3: Long Answer (10 points each) 31. Answer: Properly-labelled molecular orbital diagram. Bond order = 2. σ 2 2sσ 2 2sπ 4 2pσ 2 2pπ 2 2p. (d) Paramagnetic. 32. Answer: scandium(iii) sulfate octahydrate, dichlorine monoxide, calcium bicarbonate (or calcium hydrogen carbonate), magnesium carbide, Nb 2 O 3, CBr 4, Ca(NO 3 ) 2, Fe(CN) Answer: Drawing. Drawing. See-saw. (d) Trigonal bipyramidal. (e) sp 3 d. 34. Answer: C 6 H 5 N. C 12 H 10 N Answer: From left to right. σ: H(1s)-C(sp). σ: C(sp)-N(2p). π: C(2p)-N(2p). 3