Q: What is the formula for calculating formal charge?

$$\text{Formal Charge} = \text{number of valence electrons} - (\text{number of lone pair electrons} + \frac{1}{2} \text{number of bonding electrons})$$

Question 1

Which of the following best describes the bonding in metallic solids, such as sodium metal?

Accepted Answer

Atoms are held together by a 'sea of electrons' surrounding nuclei.

Question 2

Which Lewis symbol correctly represents the valence electrons for sulfur (S)?

Accepted Answer

S with six dots around it

Question 3

Given the electron configuration $$[Ne]3s^2$ 3p^5$, which element does this represent and what is its Lewis symbol?

Accepted Answer

Chlorine, with seven dots around Cl

Question 4

Which process is represented by the equation $$\mathrm{Na} + \mathrm{Cl} \rightarrow \mathrm{Na}^+ + \mathrm{Cl}^-$$?

Accepted Answer

Formation of an ionic bond

Question 5

Which compound would you expect to have the highest lattice energy based on the charge and size of ions?

Accepted Answer

LiF

Question 6

What is the relationship between bond length and bond enthalpy for N–N bonds?

Accepted Answer

As bond length decreases, bond enthalpy increases.

Question 7

Which molecule is an example of a resonance structure?

Accepted Answer

O$$_3$$

Question 8

Which of the following molecules is an exception to the octet rule because it has an odd number of electrons?

Accepted Answer

NO

Question 9

Which of the following statements about electronegativity is correct?

Accepted Answer

Electronegativity increases across a period and decreases down a group.

Question 10

Which bond is the most polar based on electronegativity differences?

Accepted Answer

N–F

Question 11

What is the formula for calculating formal charge?

Accepted Answer

$$	ext{Formal Charge} = 	ext{number of valence electrons} - (	ext{number of lone pair electrons} + \frac{1}{2} 	ext{number of bonding electrons})$$

Question 12

Which of the following is a correct statement about bond enthalpy?

Accepted Answer

Bond enthalpy is positive because bond breaking is endothermic.

Question 13

Which of the following molecules can expand its octet due to the presence of unfilled d orbitals?

Accepted Answer

PF$$_5$$

Question 14

Which type of bond is formed when two atoms share electrons equally?

Accepted Answer

Nonpolar covalent bond

Question 15

What is the enthalpy change ($$\Delta H) $$for the reaction $$2 \mathrm{H}_2(g) + \mathrm{O}_2(g) \rightarrow 2 \mathrm{H}_2\mathrm{O}(g)$$?

Accepted Answer

$$\Delta H = -483.6\ \mathrm{kJ}$$

Question 16

Which of the following is the correct formula for lattice energy according to Coulomb’s law?

Accepted Answer

$$E = k \frac{Q_1$ Q_2$}{d}$$

Question 17

Which of the following molecules is most likely to be brittle and have a high melting point?

Accepted Answer

NaCl

Question 18

Which of the following is a correct statement about resonance structures?

Accepted Answer

Resonance structures represent the average of multiple possible Lewis structures.

Question 19

Which molecule below is an example of a real-world application of the octet rule exception (less than an octet)?

Accepted Answer

BF$$_3$$

Question 20

Calculate the approximate enthalpy change ($$\Delta H_{rxn}) $$for the reaction $$\mathrm{CH}_4(g) + \mathrm{Cl}_2(g) \rightarrow \mathrm{CH}_3\mathrm{Cl}(g) + \mathrm{HCl}(g)$$ using the following average bond enthalpies: $$D(\mathrm{C}-\mathrm{H}) = 413\ \mathrm{kJ/mol}$$, $$D(\mathrm{Cl}-\mathrm{Cl}) = 242\ \mathrm{kJ/mol}$$, $$D(\mathrm{C}-\mathrm{Cl}) = 328\ \mathrm{kJ/mol}$$, $$D(\mathrm{H}-\mathrm{Cl}) = 431\ \mathrm{kJ/mol}.$$

Accepted Answer

$$\Delta H_{rxn} = -104\ \mathrm{kJ}$$

Basic Concepts of Chemical Bonding

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