Electronic Structure and Periodic Table

1s² 2s² 2p⁶ 3s² 3p³

Atoms of an element, X, have the electronic con­figu­ration shown above. The compound most likely formed with magnesium, Mg, is:

• Mg₃X₂

• Mg₂X

• MgX₂

• MgX₃

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Which atom below contains exactly two unpaired electrons?

• Ni

• Ca

• P

• I

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Which atom contains only one electron in the highest occupied energy sublevel?

• Mg

• Sc

• As

• Br

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The table shows the first ionization energy and atomic radius of several elements. Which of the following best helps to explain the deviation of the first ionization energy of oxygen from the overall trend?

• The atomic radius of oxygen is greater than the atomic radius of fluorine.

• The atomic radius of oxygen is less than the atomic radius of nitrogen.

• There is repulsion between paired electrons in oxygen’s 2p orbitals.

• There is attraction between paired electrons in oxygen’s 2p orbitals.

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The ionization energies for element X are listed in the table on the right. On the basis of the data, element X is most likely to be

• Be

• B

• C

• F

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For element X represented above, which of the following is the most likely explanation for the large difference between the second and third ionization energies?

• The effective nuclear charge decreases with successive ionizations.

• The shielding of outer electrons increases with successive ionizations.

• The electron removed during the third ionization is, on average, much closer to the nucleus than the first two electrons removed were.

• The ionic radius increases with successive ionizations.

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Which of the following is the electron configuration of Ag⁺ ion?

• [Kr] 5s²4d⁸

• [Kr] 5s¹4d⁹

• [Kr] 4d⁹

• [Kr] 4d¹⁰

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Which of these configurations correctly shows an atom in an excited state?

• 1s² 2s² 2p⁶ 3s² 3p⁶ 4s³

• 1s² 2s² 2p⁶ 3s² 3p⁵

• 1s² 2s² 2p⁶ 3s¹ 3p⁶

• 1s² 2s² 2p⁶ 2d¹⁰

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The photoelectron spectra of the 1s electrons of two isoelectronic species, Ca²⁺ and Ar, are shown on the right. Which of the following correctly identifies the species associated with peak X and provides a valid justification?

• Ar, because it has completely filled energy levels

• Ar, because its radius is smaller than the radius of Ca²⁺

• Ca²⁺, because its nuclear mass is greater than that of Ar

• Ca²⁺, because its nucleus has two more protons than the nucleus of Ar has

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The compound CCl₄ is nonflammable and was once commonly used in fire extinguishers. On the basis of the periodic properties, which of the following compounds can most likely be used as a fire-resistant chemical?

• BCl₃

• CH₄

• CBr₄

• PbCl₂

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