Q: Which of the following is the correct formula for calculating the formal charge on an atom?

$$\text{Formal charge} = \text{number of valence electrons} - \text{number of lone pair electrons} - \frac{1}{2} \times \text{number of bonding electrons}$$

Question 1

Which of the following best explains why a covalent bond forms between two hydrogen atoms?

Accepted Answer

The nucleus-electron attractions are greater than the nucleus-nucleus and electron-electron repulsions, resulting in a net attractive force.

Question 2

Given the bond dissociation energies: $$\mathrm{H-H} (436 kJ/$$mol), $$\mathrm{O=O} (498 kJ/$$mol), and $$\mathrm{H-O} (464 kJ/$$mol), what is the enthalpy change for the reaction $$2\mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2\mathrm{H}_2\mathrm{O}$$?

Accepted Answer

$$-484\ \mathrm{kJ}$$

Question 3

Which of the following bonds is expected to be the shortest and strongest?

Accepted Answer

$$\mathrm{C\equiv C}$$

Question 4

Which of the following statements about electronegativity is correct?

Accepted Answer

Electronegativity decreases down a group and increases across a period.

Question 5

Which molecule contains a polar covalent bond?

Accepted Answer

$$\mathrm{HCl}$$

Question 6

What is the correct Lewis structure for carbon dioxide ($$\mathrm{CO_2$}$$)?

Accepted Answer

O=C=O, with each O atom having two lone pairs

Question 7

Which of the following molecules is an exception to the octet rule due to being electron-deficient?

Accepted Answer

$$\mathrm{BF_3$}$$

Question 8

Which of the following best describes the bond in $$\mathrm{NaCl}$$?

Accepted Answer

Ionic

Question 9

What is the formal charge on the central atom in the best Lewis structure for $$\mathrm{NO_3$^-}$$?

Accepted Answer

$$0$$

Question 10

Which of the following molecules exhibits resonance?

Accepted Answer

$$\mathrm{O_3$}$$

Question 11

Which of the following is the best description of a free radical?

Accepted Answer

A molecule with an odd number of valence electrons

Question 12

Which of the following statements about bond energies is correct?

Accepted Answer

A triple bond is generally shorter and stronger than a single bond between the same two atoms.

Question 13

Which of the following is the correct order of increasing electronegativity for the series: $$\mathrm{Al, H, Na, O, P}$$?

Accepted Answer

$$\mathrm{Na \u003c Al \u003c H \u003c P \u003c O}$$

Question 14

Which of the following molecules is hypervalent?

Accepted Answer

$$\mathrm{SF_6$}$$

Question 15

Which of the following best explains why ionic compounds like $$\mathrm{NaCl}$$ have much higher melting points than covalent compounds like $$\mathrm{HCl}$$?

Accepted Answer

Ionic compounds have stronger intermolecular forces due to lattice energy.

Question 16

Which of the following is the correct Lewis symbol for a chloride ion?

Accepted Answer

$$\mathrm{Cl}^-$$ with 8 dots

Question 17

Which of the following is the correct formula for calculating the formal charge on an atom?

Accepted Answer

$$	ext{Formal charge} = 	ext{number of valence electrons} - 	ext{number of lone pair electrons} - \frac{1}{2} 	imes 	ext{number of bonding electrons}$$

Question 18

Which of the following molecules contains a central atom with an incomplete octet?

Accepted Answer

$$\mathrm{$$BeH_2$$}$$

Question 19

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

Accepted Answer

The actual electronic structure is an average of all resonance forms.

Question 20

Which of the following is the best Lewis structure for the thiocyanate ion ($$\mathrm{CNS^-}) $$based on formal charge considerations?

Accepted Answer

C triple bonded to N, single bonded to S, with the negative charge on S

Covalent Bonding and Electron-Dot Structures: Chapter 7 Study Guide

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