Ch 4. Atomic Structure And Periodic Trends Flashcards
Of the following metallic elements, which has the lowest second ionization energy?
A) Na
B) K
C) Mg
D) Ca
D
After their first ionization, Na+ and K+ both have octet electron configurations, so a second ionization to remove another electron would require a very high amount of energy. This eliminates A and B. Ionization energy decreases down a group, due to increased nuclear shielding, so it is easier to remove electrons from Ca than Mg, making choice D the answer.
When an atom of plutonium-239 is bombarded with an alpha particle, this element along with one free neutron is created:
A) Californium-240
B) Californium-241
C) Curium-242
D) Curium-243
C
The process described is transmutation, the new nucleus can be determined by writing a balanced nuclear equation. The preliminary equation to balance is this:
^239, _94 Pu + ^4, _2 x —>
^1, _0 y + ^w, _z ?
The ? represents the new element formed. Balancing mass number gives 239 + 4 = 1 + x, where x = 242; balancing the atomic number gives 94 + 2 = 0 + Z, where Z = 96. Therefore, element number 96 is curium (eliminating choices A and B), and the appropriate isotope has a mass number of 242.
Which atom has 3 unpaired electrons in its valence energy level?
A) Li
B) Be
C) C
D) N
D
Since Li has only 1 valence electron and Be has only two, neither choice A nor B can be correct. To choose between C and D, note that the valence configuration of C is 2s^2 2p^2. Thus the 2s electrons are paired leaving only 2 unpaired p electrons. N has a valence configuration of 2s^2 2p^3, and by Hund’s rule, the 3 p electrons will singly occupy the p_x, p_y, and p_z levels rather than pairing up to avoid electron repulsion.
Which of the following represents the correct ground state electronic configuration for ferrous ion, Fe ^2+?
A) [Ar] 4s^2 3d^6
B) [Ar] 4s^2 3d^4
C) [Ar] 3d^6
D) [Ar] 4s^2 3d^2
C
When answering electron configuration questions, the first step is to eliminate all answer choices that do not display the correct number of electrons. In this case, ferrous ion pocesses six electrons beyond those represented by [Ar]. This options A and D are wrong. When transition metals ionize, it is the outermost and therefore least tightly held electrons that are removed first. The 4s electrons are further from the nucleus and are less tightly held. (n=4 represents a greater radial distance from the nucleus than n=3). Thus they are the first to be removed.
Which of the following elements would be most strongly attracted to a magnetic field?
A) Mg
B) Ca
C) Cr
D) Zn
C
Diamagnetic atoms are repelled by magnetic fields and paramagnetic atoms are attracted to magnetic fields. Paramagnetic atoms have unpaired electrons in their valence orbitals. Mg and Ca are in the same group and have the same valence configuration, so both cannot be the right answer. Zn is at the end of the d block and has a valence shell with all of its electrons paired. Cr only has five electrons in its 3d subshell, resulting in five unpaired electron orbitals. Cr is the only choice that is paramagnetic and would be attracted to a magnetic field.
Which of the following colors would appear as a bright band in an emission spectrum of a yellow sodium vapor lamp?
A) Yellow, indicating a lesser wavelength than ultraviolet light
B) Yellow, indicating a greater wavelength than ultraviolet light
C) Blue, indicating a lesser wavelength than ultraviolet light
D) Blue, indicating a greater wavelength than ultraviolet light
B
All visible light has a greater wavelength than ultraviolet, eliminating choices A and C. The sodium lamp glows yellow and would therefore emit a yellow band on a dark background.
If the question asked where dark bands would have been in an absorption spectrum, several lines would be seen in regions other than yellow since those colors are absorbed.
Which of the following atoms/ions has electrons in the subshell of highest energy?
A) CI-
B) Ca2+
C) Cr+
D) As
D
Electron energy level is determined by the first two quantum numbers. Given Cl- = [Kr], Ca2+ = [Ar], Cr+ = [Ar] 3d5, and As = [Ar] 4s^2 3d^10 4p^3, arsenic contains electrons in the highest energy subshell, 4p.
Which of the following has the smallest atomic or ionic radius?
A) CI
B) Ar
C K+
D) Ca2+
D
All four answer choices have the same number of electrons and the same clectron configuration. Ca2+ has the most protons pulling on these electrons, so it will be the smallest.
Metallic character results from an element’s ability to lose electrons. On the periodic table it is expected that metallic character increases:
A) from left to right, because the decrease in electronegativity would make it easier to lose electrons.
B) from left to right, because the decrease in atomic radius would result in more stable positive ions.
C) from right to left, because the decrease in ionization energy would make it easier to lose electrons.
D) from right to left, because the decrease in electron affinity would result in more stable positive ions.
C
Choice A is eliminated because electronegativity increases from left to right on the periodic table. Choice B is eliminated because the stability of positive ions increases as you go up and to the left on the periodic table. Finally, choice D is eliminated since electron affinity is the energy released upon gaining an electron and does not relate to the stability of a positive ion. Choice C is the correct answer because ionization energy, or the energy required to remove an electron, decreases from right to left due to a decrease in effective nuclear charge.
