Chemistry 1 st Midterm Exam 2010/11/5

Transcription

1 Periodic Table of Elements Chemistry 1 st Midterm Exam 1/11/5 Formulae E = hν ν = R(1/n 1 1/n ), R =.9x1 15 Hz = h/mv = h/p E n = n h /8mL 1/m e v = hν Φ η + V ( x, y, z) ψ ( x, y, z) = Eψ ( x, y, z) m Hψ = Eψ Constants R = 8.14 J / mol K 1 atm = 76 Torr = 1.1x1 5 Pa =.81 L atm / K mol c = m/s = 8.14 L kpa / K mol h = J s Mass of e, m e = kg Nature Exponential Base e =.7188

2 1 Suppose the electron is in a 1sorbital of a H atom. What is the probability of finding the electron in a small region a distance.5a from the nucleus relative to the probability of finding it in the small region located right at the nucleus? The 1s orbital wave function of a H atom: (no need of calculation, just write down the simplest equation expression of the correct answer). 1 (,, ) ( ) 1/ r / a ψ r θ φ = e, a = 5.9 pm (6%) π a Write the electron configuration and expect the number of unpaired electrons for the following elements in the groundstate: (a) copper; (b) sulfur; (c) tin. (9%) Consider a particle of mass m in a 1dimensional box between two rigid walls a distance L apart, and answer the following questions..1 What s the wave length of this particle of quantum number n = 5? (%). Are any of the energy levels of this particle degenerate? If so, find one set of quantum numbers as an example. (%). If the particle can absorb green light and transition from n = 1 to n =. After changing the size of the box from L to L, this particle absorbs red light for the same transition. Is L > L or L < L? (%).4 Is the statement: when n =, the energy of this particle is, it is also called the zeropoint energy, correct? Why? (+%) 4 (a) X +, Y +, and O are isoelectronic. What is the element Y? (%) (b) Write the three quantum numbers {n, l, m l } of the valence electron of a X atom in the ground state. (%) (c) Which has the largest atomic radius, X, Y, or O? (%) (d) Which has the largest second ionization energy, X or Y? (use the element symbols for answering (a), (c), (d)) (%) 5 Please select the most correct answer for each following question. (% each; 14% total) 5.1 For a compound AB, the greater the electronegativity difference between the two bonded atoms, the (a) greater the bond strength (b) greater the ionic character of the bond (c) longer the bond length (d) more unstable the bond (e) less soluble in water 5. For a compound AB, the greater the formal charge on the two bonded atoms, the (a) greater the bond strength (b) greater the ionic character of the bond (c) longer the bond length (d) more unstable the bond (e) less soluble in water

3 5. What is the correct order of the following bonds in terms of decreasing polarity? (a) NCl, PCl, AsCl (b) AsCl, PCl, NCl (c) AsCl, NCl, PCl (d) PCl, AsCl, NCl (e) PCl, NCl, AsCl 5.4 In the gaseous phase, which of the following diatomic molecules would have the most covalent character? (a) CsBr (b) CsF (c) NaCl (d) NaF (e) LiBr 5.5 Which of the following has the lowest lattice energy? (a) CsBr (b) CsF (c) NaCl (d) NaF (e) LiBr 5.6 Which of the following is polar? (a) XeF 4 (b) PCl 5 (c) ICl 4 (d) SF 6 (e) IF All of the following have an angular shape except (a) HOCl (b) S (c) I (d) ClO 6 Consider the following molecules. (% each; 6% total) BF C H 4 (Allene, nonpolar molecule) N O HXeO 4 NO SF 4 CH O 6.1 Which molecules violate the octet rule? 6. Which molecules are radicals? 6. Which molecules may have resonance structures? 7 Please draw the most stable Lewis structure of the following molecules. All of the lone pairs have to be drawn clearly and determine the formal charge on each atom. If there are several resonance structures, please just write one of the most favorite structure. (4% each; 1% total) 7.1 BrO 7. SO 7. XeO

4 8 (% each; 6% total) 8.1 This is a neutral molecule. E is an element on the Period. Please calculate the formal charge and the number of the valence electron of the element E. Please identify the element E 8. This is an anion with the charge of 1. E is an element of the main group on the Period 4. Please calculate the formal charge and the number of the valence electron of the element E. Please identify the element E 9 (% each; 4% total) Do you expect the ionization energy of H to be 91 higher or lower than that of H? 9 higher or lower than that of H? 1 (4% each; 8% total) 11 What do you predict for the hybridization of the central C atom, and the number of σ and π bonds in HCN? 1 What do you predict for the hybridization of the central C atom, and the number of σ and π bonds in CO? 11. (14% total) 111(6%) Sketch the energy level diagram of O including only MO formed by the s and p atomic orbitals. Name these MO. Place the electrons of O in these MO. Explain why O is paramagnetic? 11 (%) In a photoelectron spectrum of N, you would expect the electrons coming off with the highest kinetic energy to be associated with which molecular orbital? (a) 1s N, (b) σ s, (c) π p, (d) σ p z, (e) π* p 11 (%) If you remove one electron from N what will happen to its bond length? (a) increase, (b) decrease, (c) remain the same 114 (4%) What do you predict for the bond orders of N, O, O, and 1. (1% each; 4% total) What do VSEPR, LCAO, LUMO, and HOMO stand for? Please write them in English. + O 4

5 Solution 1 [modified example 1.9, exercises 1.9] probability density: 1 θ φ = π a r / a ψ ( r,, ) ( ) e (%) here, the ration of the probability = the ration of the probability density ψ.5a ψ () 1 a ( ) e ) π a = 1 ( ) e π a ( 1 / a = e =.7 (equation %, result %, either e 1 or.7 is correct) [modified exercises ] Cu: [Ar]d 1 4s 1, 1 unpaired electron; S: [Ne]s p 4, unpaired electrons; Sn: [Kr]4d 1 5s 5p, unpaired electrons (each electron configuration %, each # of unpaired electrons %, total 1%) (a) L/5 (%) (b) No (%) (c) L > L (%) (d) No. The lowest possible energy of this particle is always >. (+%) 4 (a) Y = Al ; (b) {,, } ; (c) Na ; (d) Na (+++%) 5 51 (b) 5 (d) 5 (b) 54 (e) 55 (a) 56 (e) 57 (c) (% each) 6 (% each) 6.1 Ans: BF, HXeO 4, SF4, NO, CH O (% each, 答錯一個扣 1 分, 答錯兩個就 分 ) 6. Ans : NO, CH O (% each, 答錯一個扣 1 分, 答錯兩個就 分 ) 6. Ans : N O, HXeO 4, NO (% each, 答錯一個扣 1 分, 答錯兩個就 分 ) 5

6 7 (4% each, 每小題 4 分, 答錯一個扣 1 分, 答錯 4 個就 分 ) (% each) 8.1 formal charge = (1%) number of valence electrons=6 (1%) Element E is S. (1%) 8. formal charge = + (1%) number of valence electrons=7 (1%) Element E is Br. (1%) lower (%) 9 lower (%) sp hybridization for the central C atom of HCN (%) σ and π bonds for HCN (%) 1 sp hybridization for the central C atom of CO (%) σ and π bonds for CO (%) 6

7 Because there are two unpaired electrons on π p *, O is paramagnetic. (1%) Sketch the energy level diagram of O (%, 答錯一個扣 1 分, 答錯兩個就 分 ) Name these MO. (%, 答錯一個扣 1 分, 答錯兩個就 分 ) Place the electrons of O in these MO. (1%) 11 d (%) 11 a (%) 114,, 1.5,.5 (4%, 答錯一個扣 1 分 ) 1. 英文單字必須相同才給分 VSEPR: valence shell electron pair repulsion (1%) LCAO: linear combination of atomic orbitals (1%) LUMO: lowest unoccupied molecular orbital (1%) HOMO: highest occupied molecular orbital (1%) 7