Midterm Exam 2 Practice

How many magnesium atoms are in the formula for magnesium nitride?

• 1

• 4

• 3

• 2

Answer explanation

Magnesium nitride has the formula Mg3N2, indicating there are 3 magnesium (Mg) atoms in each formula unit. Therefore, the correct answer is 3.

Tags

NGSS.MS-PS1-1

The compound CO is called ________.

• carbon monoxide

• oxygen carbide

• carbon oxide

• carbon monoxygen

Answer explanation

The compound CO is called carbon monoxide, which consists of one carbon atom and one oxygen atom. The other options do not accurately describe this chemical compound.

Which pair of bonded atoms has the largest difference in electronegativity?

• C — F

• N — N

• C — O

• C — N

Answer explanation

The C — F bond has the largest electronegativity difference (about 1.5) due to fluorine's high electronegativity compared to carbon. In contrast, N — N, C — O, and C — N have smaller differences.

Which of the following has the highest lattice energy?

• CaO

• MgO

• NaCl

• BaO

Answer explanation

MgO has the highest lattice energy due to its smaller ionic size and higher charge (+2 for Mg and O) compared to the other compounds, leading to stronger electrostatic forces between the ions.

Tags

NGSS.HS-PS1-3

NGSS.HS-PS2-4

Rank the following salts in increasing order of their lattice energy: Lithium Fluoride (LiF), Lithium Bromide (LiBr), Beryllium Fluoride (BeF2), Beryllium Bromide (BeBr2).

• LiF < BeF2 < LiBr < BeBr2

• LiBr < LiF < BeBr2 < BeF2

• BeF2 < BeBr2 < LiF < LiBr

• BeBr2 < BeF2 < LiBr < LiF

Answer explanation

Lattice energy increases with charge and decreases with size. BeBr2 has the lowest lattice energy due to larger Br- ions, followed by BeF2. LiBr has a higher lattice energy than BeF2, and LiF has the highest due to smaller ions.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS2-4

What is the formula for barium fluoride?

• Ba2F3

• Ba2F

• BaF

• BaF2

Answer explanation

The formula for barium fluoride is BaF2. Barium (Ba) has a +2 charge, and each fluoride (F) has a -1 charge. To balance the charges, two fluoride ions are needed for each barium ion, resulting in BaF2.

Calculate the formal charge on C in the molecule CH4.

• 4

• 2

• 0

• 3

Answer explanation

To calculate the formal charge on C in CH4, use the formula: Formal Charge = Valence Electrons - (Non-bonding Electrons + 1/2 Bonding Electrons). C has 4 valence electrons, 0 non-bonding, and shares 8 bonding electrons, resulting in a formal charge of 0.

Which of these substances has a formula incorporating a triple bond?

• C₂H₂

• C₂H₄

• C₂Cl₄

• N₂H₄

Answer explanation

C₂H₂, also known as acetylene, contains a triple bond between the two carbon atoms. The other options, C₂H₄ (ethylene), C₂Cl₄ (carbon tetrachloride), and N₂H₄ (hydrazine), do not have triple bonds.

How many lone pairs of electrons are found in the Lewis structure of hydrazine (N₂H₄)?

• 1

• 2

• 4

• 8

Answer explanation

In the Lewis structure of hydrazine (N₂H₄), each nitrogen atom has one lone pair of electrons, totaling 2 lone pairs. Additionally, there are 2 lone pairs on the hydrogen atoms, leading to a total of 4 lone pairs.

Which of the following species exhibit resonance/delocalization?

I. HCN

II. O₃

III. CO₃²⁻

• II, III

• I, II

• I only

• I, II, III

Answer explanation

Resonance occurs in species with multiple valid Lewis structures. O₃ (ozone) and CO₃²⁻ (carbonate) exhibit resonance due to their ability to have different arrangements of electrons. HCN does not show resonance.