SDSMT - Exam 2 Review

What is the molecular shape and polarity for xenon tetrafluoride?

• Square Planar and non-polar

• Tetrahedral and non-polar

• Trigonal planar and non-polar

• Bent and polar

• Square planar and polar

Answer explanation

Xenon tetrafluoride (XeF4) has a square planar molecular shape due to the presence of six electron pairs around the central xenon atom, with four bonding pairs and two lone pairs. The symmetric arrangement of the fluorine atoms around the xenon atom results in the cancellation of the individual bond dipoles, making the molecule non-polar.

How many polar bonds does CCl₄ have in its structure?

• 0

• 1

• 2

• 3

• 4

Answer explanation

CCl4 has a tetrahedral structure with carbon at the center and four chlorine atoms surrounding it. Each carbon-chlorine bond is polar due to the difference in electronegativity between carbon and chlorine. Therefore, CCl4 has 4 polar bonds in its structure.

According to the octet rule, which of the elements will have a tendency to lose 2 electrons?

• Potassium

• Sulfur

• Oxygen

• Strontium

• Cesium

Answer explanation

According to the octet rule, elements tend to gain, lose, or share electrons to achieve a stable electron configuration with eight electrons in their outermost shell. Strontium, a Group 2 element, has two valence electrons and will have a tendency to lose 2 electrons to achieve a stable octet configuration.

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NGSS.HS-PS1-2

What is the ground-state electron configuration of calcium?

• 1s²2s²2p⁶

• 1s²2s²2p 3s²4s⁸

• 1s²2s²2p⁶3s²3p⁶4s²

• 1s²2s²2p⁶3s²

• 1s²2s²2p⁶3s²3p⁶4s¹

Answer explanation

The ground-state electron configuration of calcium is determined by filling the orbitals in order of increasing energy. Calcium has 20 electrons, so the configuration is 1s²2s²2p⁶3s²3p⁶4s². This corresponds to the correct choice, which is 1s²2s²2p⁶3s²3p⁶4s².

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According to VSEPR theory, the shape of an ammonium ion, NH₄⁺, is most similar to:

• Trigonal pyramidal, 109.5°

• Trigonal planar, 120°

• Bent, 120°

• Trigonal pyramidal, 120°

• Trigonal planar, 90°

Answer explanation

According to VSEPR theory, the shape of an ammonium ion, NH4+, is most similar to trigonal pyramidal with a bond angle of 109.5°. This is because the central nitrogen atom is surrounded by four hydrogen atoms, forming a tetrahedral arrangement. The trigonal pyramidal shape is a result of the repulsion between the electron pairs, which causes them to spread out as far as possible.

Which of the following is true about Fe²⁺?

• Fe²⁺ is paramagnetic with 0 unpaired electrons

• Fe²⁺ is paramagnetic with 2 unpaired electrons

• Fe²⁺ is paramagnetic with 4 unpaired electrons

• Fe²⁺ is paramagnetic with 5 unpaired electrons

• Fe²⁺ is diamagnetic

Answer explanation

Fe²⁺ is paramagnetic with 4 unpaired electrons because it has an electron configuration of [Ar] 3d⁶. In this configuration, there are 4 unpaired electrons in the 3d orbitals, making it paramagnetic. The other options are incorrect as they either state the wrong number of unpaired electrons or incorrectly classify Fe²⁺ as diamagnetic.

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According to periodic trends, arrange the following ions, potassium K⁺, magnesium Mg²⁺, and aluminum Al³⁺ in order of increasing ionic size.

• K⁺ < Al³⁺ < Mg²⁺

• K⁺ < Mg²⁺ < Al³+

• Al³+ < K⁺ < Mg²⁺

• Al³+ < Mg²⁺ < K⁺

• Cannot predict the size trend

Answer explanation

In the periodic table, ionic size decreases across a period and increases down a group. As we move from left to right, potassium (K+), magnesium (Mg2+), and aluminum (Al³+) are in the same period. The correct order of increasing ionic size is Al³+ < Mg2+ < K+, as the charge increases and the number of electrons decreases, making the ion smaller.

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Which element has the electron configuration 1s²2s²2p⁶3s²3p⁶4s²3d⁵?

• Tc

• Mo

• Mn

• Fe

• Cr

Answer explanation

The element with the electron configuration 1s²2s²2p⁶3s²3p⁶4s²3d⁵ is Manganese (Mn). This configuration corresponds to a total of 25 electrons, which matches the atomic number of Mn. The other options, Tc, Mo, Fe, and Cr, have different electron configurations and atomic numbers.

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Which of the following would be polar?

• CH₄

• BF₃

• C₂H₂

• CO₂

• CH₃OH

Answer explanation

A polar molecule has a net dipole moment due to the presence of polar bonds. Among the given options, CH3OH (methanol) is the only polar molecule. The other molecules either have nonpolar bonds or their polar bonds cancel each other out due to symmetry, resulting in a nonpolar molecule.

Which element has four valence electrons in it's Lewis symbol?

• sulfur

• iron

• germanium

• indium

• zinc

Answer explanation

Germanium has four valence electrons in its Lewis symbol. Valence electrons are the outermost electrons in an atom and are involved in chemical bonding. Germanium, a group 14 element, has a similar electron configuration to carbon and silicon, with four valence electrons. This allows it to form covalent bonds with other elements and participate in semiconductor applications.

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