Unit 1

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

• MgX

• MgX₂

• MgX₃

• Mg₃X₂

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A 23.0g sample of a compound contains 12.0g of C, 3.0g of H, and 8.0g of O. Which of the following is the empirical formula of the compound?

• CH₃O

• C₂H₆O

• C₃H₉O₂

• C₄H₁₂O₂

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NGSS.HS-PS1-3

Based on the ionization energies of element X given in the table above, which of the following is most likely the empirical formula of an oxide of element X?

• XO₂

• X₂O

• X₂O₃

• X₂O₅

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If Na reacts with chlorine to form NaCl, which of the following elements reacts with Na to form an ionic compound in a one-to-one ratio, and why?

• K, because it is in the same group as Na.

• Mg, because its mass is similar to that of Na.

• Ar, because its mass is similar to that of Cl.

• Br, because it has the same number of valence electrons as Cl.

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The percentage of silver in a solid sample is determined gravimetrically by converting the silver to Ag⁺(aq) and precipitating it as silver chloride. Failure to do which of the following could cause errors in the analysis?

• I only

• I and IV

• II and III

• I, III, and IV

Which of the following represents a pair of isotopes?

• A) Atom I: Atomic Number 5, Mass Number 14; Atom II: Atomic Number 14, Mass Number 14

• B) Atom I: Atomic Number 5, Mass Number 7; Atom II: Atomic Number 14, Mass Number 14

• C) Atom I: Atomic Number 7, Mass Number 13; Atom II: Atomic Number 7, Mass Number 14

• D) Atom I: Atomic Number 8, Mass Number 10; Atom II: Atomic Number 16, Mass Number 20

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NGSS.HS-PS1-8

The photoelectron spectra of the 1s electrons of two isoelectronic species, Ca²⁺ and Ar, are shown above. 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 complete photoelectron spectrum of a pure element is represented above. Which of the following correctly identifies both the element and the atomic orbitals represented by peak X and peak Y?

• A

• B

• C

• D

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In 1.00 mol of potassium zirconium sulfate trihydrate, K4Zr(SO4)4•3 H2O, there are

• 3 × 6.02 × 10^23 hydrogen atoms

• 6.02 × 10^23 sulfur atoms

• 4 × 6.02 × 10^23 potassium atoms

• 4 moles of zirconium atoms

The effective nuclear charge experienced by the outermost electron of Na is different than the effective nuclear charge experienced by the outermost electron of Ne. This difference best accounts for which of the following?

• Na has a greater density at standard conditions than Ne.

• Na has a lower first ionization energy than Ne.

• Na has a higher melting point than Ne.

• Na has a higher neutron-to-proton ratio than Ne.

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