Question 1

Which of the following statements best explains why covalent bonds form between nonmetal atoms?

Accepted Answer

Nonmetals have high effective nuclear charge and high ionization energy, so they attract and share electrons tightly.

Question 2

Which of the following bonds has the highest bond energy, and why?

Accepted Answer

H-F, because fluorine is the smallest atom, resulting in the shortest and strongest bond.

Question 3

Given the reaction: $$\mathrm{C_2H_4 + H_2$ \rightarrow C_2H_6}$$, and the following bond energies: $$\mathrm{C-H} (413 kJ/$$mol), $$\mathrm{C=C} (614 kJ/$$mol), $$\mathrm{C-C} (347 kJ/$$mol), $$\mathrm{H-H} (432 kJ/$$mol), calculate $$\Delta H_{rxn}.$$

Accepted Answer

$$-127\ \mathrm{kJ}$$

Question 4

Which of the following best describes the relationship between bond order, bond length, and bond energy?

Accepted Answer

As bond order increases, bond length decreases and bond energy increases.

Question 5

Which of the following molecules would absorb the highest frequency of infrared (IR) radiation due to bond vibrations?

Accepted Answer

$$\mathrm{N_2$} ($$triple bond)

Question 6

Why do covalent compounds generally have lower melting and boiling points compared to ionic compounds?

Accepted Answer

Covalent compounds have weak intermolecular forces, so less energy is needed to separate molecules.

Question 7

Which of the following is a network covalent solid, and what property does it exhibit?

Accepted Answer

Diamond; it has a high melting point and is an electrical insulator.

Question 8

Which of the following best describes the trend in electronegativity (EN) across a period in the periodic table?

Accepted Answer

EN increases from left to right.

Question 9

Which bond is the most polar based on the difference in electronegativity (DEN)?

Accepted Answer

P–O

Question 10

Classify the bond in $$\mathrm{KCl}$$ using the difference in electronegativity (DEN) and the provided guideline: $$\Delta EN \u003e 1.7 is $$mostly ionic.

Accepted Answer

Mostly ionic

Question 11

Which of the following best explains why distilled water does not conduct electricity?

Accepted Answer

Distilled water contains only covalent molecules with no free ions.

Question 12

Which of the following compounds would you expect to have the highest melting point based on its bonding and structure?

Accepted Answer

$$\mathrm{NaCl}$$

Question 13

Which of the following best describes the physical properties of graphite?

Accepted Answer

Strong 2D layers, high melting point, electrical conductor

Question 14

Which of the following statements about bond energy is correct?

Accepted Answer

Bond energy is the energy required to break a covalent bond and is always positive.

Question 15

A molecule absorbs IR radiation at a higher frequency. What does this indicate about the bond involved?

Accepted Answer

The bond is stronger and shorter.

Question 16

Which of the following best explains why $$\mathrm{H_2O} is a $$poor conductor of electricity in its pure form?

Accepted Answer

It contains no free ions or electrons.

Question 17

Which of the following best describes the effect of atomic size on bond length and bond energy?

Accepted Answer

Larger atoms form longer, weaker bonds.

Question 18

Which of the following best describes the relationship between effective nuclear charge ($$Z_{eff}) $$and electronegativity (EN)?

Accepted Answer

As $$Z_{eff}$$ increases, EN increases.

Question 19

Which of the following best explains why the bond in $$\mathrm{Cl_2$} is $$nonpolar?

Accepted Answer

The two chlorine atoms have identical electronegativities, so electrons are shared equally.

Covalent Bonding, Bond Energies, and Bond Polarity: Study Notes

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