CLEP Chemistry - Problem Drill 10: Atomic Structure and Electron Configuration

Transcription

1 CLEP Chemistry - Problem Drill 10: Atomic Structure and Electron Configuration No. 1 of 10 Instructions: (1) Read the problem statement and answer choices carefully (2) Work the problems on paper as 1. How many electrons does Sr 2+ have? (A) 38 (B) 36 (C) 40 (D) 88 (E) 2 This would be a neutral Sr atom. B. Correct. This would be for a +2 ion. This would be a -2 ion. This is using mass number rather than atomic number to determine electrons. E. Incorrect. The charge is the number of protons electrons, not the number of electrons. Sr s atomic number is 38, which means as a neutral atom it has 38 electrons. Sr +2 has had 2 electrons removed. It now has 36 electrons. The correct answer is (B).

2 No. 2 of Which is the correct electronic configuration for As? (A) 1s 2s 2p 3s 3p (B) 1s 2s 2p 3s 3p _ _ _ (C) 1s 2s 2p 3s 3p 4s 3d 4p (D) 1s 2s 2p 3s 3p 4s 3d 4p _ _ (E) 1s 2s 2p 3s 3p 4s 3d 4p _ This one doesn t have 33 electrons. This one doesn t have 33 electrons. This one didn t put one electron in each 4p orbital before doubling up. D. Correct! This one has the correct electrons configuration for As. E. Incorrect. One of the 4p orbitals is missing and two electrons are paired when they do not need to be. As has 33 electrons. Choices A & B don t have 33 electrons. Choice C has electrons doubled up in a 4p orbital while another 4p orbital is empty. Choice D is correct. Choice E is missing one of the 4p orbitals and it has two electrons paired when it doesn t have to. The correct answer is (D).

3 No. 3 of Which of the following is correct for Si? (A) 1s 2 2s 2 2p 6 3s 2 3p 2 (B) 1s 2 1p 6 2s 2 2p 4 (C) 1s 2 2s 2 2p 4 3s 2 3p 4 (D) 1s 2 2s 2 2p 2 3s 2 3p 2 (E) 1s 2 2s 2 2p 6 2d 8 A. Correct! This one is correct for Si. There is no 1p subshell. This one doesn t have 14 electrons. This one doesn t have 14 electrons. There is no 2d subshell. Si has 14 electrons Choices C & D don t have 14 electrons Choice B has a 1p subshell, which does not exist. Choice E has a 2d subshell, which does not exist. The correct answer is (A).

4 No. 4 of Which of the following is correct for Se? (A) [Ar] 1s 2 2s 2 2p 6 3s 2 3p 4 (B) [Ar] 4s 2 3d 10 4p 4 (C) [Kr] 4s 2 3d 10 4p 4 (D) [Kr] 1s 2 2s 2 2p 6 3s 2 3p 4 (E) 1s 2 2s 2 2p 6 3s 2 3p 4 When using noble gas notation, you don t start at 1s. B. Correct! This is correct for Se. Remember chose the noble gas that is closest without going over to the number of electrons needed. D. Incorrect! When using noble gas notation, you don t start at 1s. Use a noble gas to represent the inner electrons. Se has 34 electrons. The noble gas closest to 34 without going over is Ar (18). Choice A starts at 1s after using Ar this is not correct. Choice B starts where Ar left off. Choice C and D use the wrong noble gas choose the one closest to 34 without going over. Choice E does not use a noble gas to represent the inner electrons. The correct answer is (B).

5 No. 5 of Which is the invalid quantum number set below? (A) 1, 1, -1, - ½ (B) 2, 0, 0, + ½ (C) 3, 2, 2, + ½ (D) 2, 1, 1, + ½ (E) 2, 1, -1, + ½ A. Correct. This is for a 1p subshell, which doesn t exist. This is for a 2s on line 0 with an up arrow, which is all possible. This for a 3d on line 2 with an up arrow, which is all possible. This is for a 2p on line 1 with an up arrow, which is possible. E. Incorrect. This is for a 2p on line -1 with an up arrow, which is possible. Set A is for a 1p subshell, which does not exist. The rest of the sets are OK. The correct answer is (A).

6 No. 6 of Which of the following is the electron configuration for Na in Na 2 O? (A) 1s 2 2s 2 2p 6 3s 1 (B) 1s 2 2s 2 2p 6 3s 2 (C) 1s 2 2s 2 2p 6 (D) 1s 1 2s 1 2p 3 3s 1 3p 3 4s 1 (E) 1s 2 2s 2 2p 5 This doesn t have 10 electrons. This doesn t have 10 electrons. C. Correct! This one has 10 electrons correctly placed. This one only puts half the number of electrons in each orbital that are necessary. This has one less electron than it is. Na in Na 2 O is Na +1 Na has 11 electrons, so Na +1 will have 10 electrons. Only answers C & D have 10 electrons. Answer D uses only half as many electrons as possible in each subshell. Choice E gives one fewer electron. The correct answer is (C).

7 No. 7 of Which is the correct electronic configuration for Al? (A) [Ne] 3s 2 3p 1 (B) [He] 3s 2 3p 1 (C) [Ne] 1s 2 2s 1 (D) [He] 1s 2 2s 1 (E) [Ne] 2s 3 A. Correct. This one has 13 electrons with the correct noble gas configuration. This one doesn t have 13 electrons. When using noble gas configuration, you don t begin with 1s. This one doesn t have 13 electrons. This configuration has 3 electrons in an s subshell which can only hold up to 2 electrons. Al has 13 electrons. Ne has 10 electrons & H has 2 electrons. Only answers A & C have 13 electrons. Answer D starts over with 1s, not where Ne left off. Choice E has three electrons in an s subshell when s subshells can only hold 2 electrons. The correct answer is (A).

8 No. 8 of The process of excitation is? (A) The release of an electron. (B) The gain of an electron. (C) The promotion of an electron to a higher energy level. (D) The return of an electron to its ground state. (E) The absorption of light by the nucleus. An electron is not released in this process. An electron is not gained in this process. C. Correct! Excitation is the promotion of an electron after it absorbs energy. The return of an electron to its ground state is relaxation. Electrons absorb the light, not the nucleus. Excitation is the process of an electron absorbing energy and being promoted to a higher energy level. The correct answer is (C).

9 No. 9 of Effective nuclear charge is. (A) Always higher than the actual nuclear charge. (B) Always lower than the actual nuclear charge. (C) Relates to the actual charge differently for metals & nonmetals. (D) None of the above (E) All of the above The electrons are shielded from the nucleus. B. Correct. The shielding from the nucleus lowers the effective charge of the nucleus. The relationship is always the same. Look carefully there is a correct answer. Look carefully there is only one correct answer. The effective nuclear charge is the charge felt by an outer electron that is shielded from the nucleus by inner electrons. Since the outer electron is shielded form the nucleus by other electrons, the effective nuclear charge is always less than the actual nuclear charge. The correct answer is (B).

10 No. 10 of Which of the following sets of quantum numbers is not possible? (A) 1, 0, 0, - ½ (B) 2, 0, -1, + ½ (C) 2, 1, -1, + ½ (D) 3, 2, 1, + ½ (E) 4, 3, -2, + ½ 1s with a down arrow on line 0 is allowed. B. Correct. There is no -1 line in the 2s subshell. 2p with an up arrow on the -1 line is allowed. An up arrow on the 1 line in a 3d subshell is allowed. An up arrow on a -2 line of the 4d subshell is allowed. The second set is an 2s subshell. The 2s subshell only has 1 orbital, which means the 3 rd number has to be 0. The correct answer is (B).