CHEM 201 Problems Chapter 7, Spring 2008

Recitation 03 1. Quantum Numbers: Consider the element Arsenic (As, Z = 33) in the ground state. Write the full electronic configuration of the ground state. a. How many electrons have ml = 0? b. How many electrons have l = 0? c. How many electrons have ml = +1? d. How many electrons have ms=+1/2 (assume the 4p3 spins are all upwards)? Solution: As Is2 2s2 2p6 3s2 3p6 4s2 3d10 3p3 (a) 15; (b) 8; (c) 7; (d) 18 Chapter 7: Exercise 60 Which of the following sets quantum numbers are not allowed? For the sets of quantum numbers that are incorrect, state what is wrong in each set. a. n = 3, l = 3, ml = 0, ms = -1/2 b. n = 4, l = 3, ml = 2, ms = -1/2 c. n = 4, l = 1, ml = 1, ms = +1/2 d. n = 2, l = 1, ml = -1, ms = -1 e. n = 5, l = -4, ml = 2, ms = +1/2 f. n = 3, l = 1, ml = 2, ms = -1/2 Solution: (a) Not allowed. Because when n = 3, l can not be 3 (b) Allowed (c) Allowed (d) Not allowed. Because mS value can not be -1 (e) Not allowed. Because l can not be negative (f) Not allowed. Because when l = 1, ml can not be 2. Chapter 7: Exercise 65 Give the maximum number of electrons in an atom that can have these quantum numbers. a. n = 4 b. n = 5, ml = +1 c. n = 5, ms = +1/2 d. n = 3, l= 2 e. n = 2, l = 1 Solution: (a) 32; (b) 8; (c) 25; (d) 10; (e) 6 Do yourself sample exercise 75 & 76 from Chapter 7 2. Electron configurations in atoms and ions Write the closed shell notation for the following elements in the ground state, by merely looking at the location of the element in the periodic table. Mo, Dy, Os, Ba, Te, Nd Solution: Mo: [Kr] 5s1 4d5 (d-block transition element) Dy: [Xe] 6s2 4f10 6s2 (f-block transition element, Group of Lanthanide) Os [Xe] 6s2 4f14 5d6 (d-block transition element) Ba [Xe] 6s2 (II group, alkaline earth metal) Te [Kr] 4d10 5s2 6p4 (VI group, semi-metal) Nd [Kr] 6s2 4f4 (f-block transition element, Group of Lanthanide) Chapter 8: Exercise 35 Which of the following ions have noble gas electron configuration? a. Fe2+, Fe3+, Sc3+, Co3+ Solution: (a) Sc3+ 3. Bond polarity Chapter 8: Exercise 23 Predict the order of increasing electronegativity in each of the following groups of elements without using Fig 8.3 a. C, N, O b. S, Se, Cl c. Si, Ge, Sn d. Tl, S, Ge Solution: The electronegativity in general increases across a period from left to right and decreases down in a group. Therefore, the answers for exercise 8.23 would be (a) C < N < O, (b) Se < S < Cl, (c) Sn < Ge < Si, (d) Tl < Ge < S Chapter 8: Exercise 25 Without using Fig 8.3 predict which bond in each of the following groups will be most polar. a. C-F, Si-F, Ge-F b. P-Cl or Si-Cl c. S-F, S-Cl, S-Br d. Ti-Cl, Si-Cl, Ge-Cl Solution: The most polar bond will be (a) Ge – F; (b) P – Cl ; (c) S – F ; (d) Ti – Cl