- Covalent and ionic substances
- Covalent and ionic bonds
- Lewis symbols and Lewis dot structues
- The octet rule and formal charges
- Exceptions to the octet rule
- Covalent bond and ionic bond
- 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 law for the calculation of various thermochemical energy
- Dipole moment
- Dipole moment and shape of molecules

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

**Give the Lewis symbol for Be.****Skill:**Give the Lewis symbol for one of the main group element**How many valence electrons are there for the element S?****Skill:**Evaluate numbers of valence electrons from group numbers and from electronic configurations. Elements O, S, Se, and Te all have 6 valence electrons.**Draw the resonance structures of NO**_{2}.**Solution:**Here are some suggested example. . .. .. N N N N / \\ // \ / \\ // \ O O O O O O O O . .

The paired electrons are not shown here.**What is the formal charge of N in the dot structure**. N / \\ O O

**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?**What is the bond order for the N-O bond in NO**_{2}?**Discussion:**Four resonance structure have been given, and all indicate a bond order of 1.5 for

[O-N=O] <=> [O=N-O].**What quantities are required in order to calculate the latice energy of NaCl?****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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