Chemical Bonding - A Review

• Use subheadings to create a summary of concepts used in chemical bonding.

Chemical Bonding - A Review

This quiz will cover the following topic:

• Covalent and ionic substances
• Covalent and ionic bonds
• Lewis symbols and Lewis dot structures
• The octet rule and formal charges
• Exceptions to the octet rule
• Covalent bonds and ionic bonds
• Count number of unshared valence electron pairs
• Resonance Structures
• Calculation of lattice energy
• Calculate enthalpy of reaction from bond energy or from energy of formation
• Use of Hess's Law for the calculation of various thermochemical energies
• Dipole moment
• Dipole moment and shape of molecules

Here are some problems related to Lewis dot structure, resonance, and formal charges. The last question is intended to direct you to a more realistic problem.

Confidence Building Questions

1. Give the Lewis symbol for $$\ce{Be}$$.

Hint: Give one of $$\textrm{Be:}$$, $$\textrm{:Be}$$, or $$\ce{.Be.}$$

Skill: Give the Lewis symbol for one of the main group elements.

2. How many valence electrons are there for the element $$\ce{S}$$?

Hint: There are 6 valence electrons for $$\ce{S}$$.

Skill: Evaluate numbers of valence electrons from group numbers and from electronic configurations. Elements $$\ce{O}$$, $$\ce{S}$$, $$\ce{Se}$$, and $$\ce{Te}$$ all have 6 valence electrons.

3. Draw the resonance structures of $$\ce{NO2}$$.

Hint: See below

Solution: Here are some suggested examples.

.      .     ..     ..
N      N     N      N
/  \\  // \   / \\  // \
O   O  O   O O   O  O   O
.          .

The paired electrons are not shown here.
4. What is the formal charge of $$\ce{N}$$ in the following dot structure?
.
N
/  \\
O     O

Hint: Number of electrons around N = 1 + (6/2)

Skill: Evaluate the formal charge of any atom of any dot structure.
What is the formal charge for the resonance structure having the odd electron on the oxygen atom?

5. What is the bond order for the $$\ce{N-O}$$ bond in $$\ce{NO2}$$?

Hint: Bond order = 1.5

Discussion: Four resonance structures have been given, and all indicate a bond order of 1.5 for $$\ce{[O-N=O]}$$ <=> $$\ce{[O=N-O]}$$.

6. What quantities are required in order to calculate the lattice energy of $$\ce{NaCl}$$?

Hint: Huum! This sounds like a real-world problem.

Skill: Solving real-world problems requires you to know what information to look for before the problem is solvable. This is one of those problems.

In an exercise or an open-book test, we can ask you to evaluate the lattice energy of a salt, and you need to find the various data. Since the CAcT quiz is an open-book test, this type of problem should have been given, but you will not have this type of problem in this quiz.

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