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Chapter 9: Problem 90

Are the following statements true or false? (a) Formal charges represent actual separation of charges. (b) \(\Delta H_{\mathrm{rxn}}^{\circ}\) can be estimated from the bond enthalpies of reactants and products. (c) All secondperiod elements obey the octet rule in their compounds. (d) The resonance structures of a molecule can be separated from one another.

Short Answer

Expert verified
Statement (a) is false. Statement (b) is true. Statement (c) is false. Statement (d) is false.

Step by step solution

01

Statement (a)

Formal charges do not necessarily indicate real charge separation. They are a bookkeeping method used in Lewis structures to denote the 'ownership' of electrons in molecules. So, the statement is false.
02

Statement (b)

The enthalpy change of a reaction, \( \Delta H_{\mathrm{rxn}}^{\circ} \), can indeed be estimated based on the bond enthalpies of reactants and products according to Hess's law. This means the statement is true.
03

Statement (c)

While the octet rule is often useful for understanding the structures of many compounds, not all compounds obey it. Especially, elements from the second period, such as Beryllium (Be), have less than eight electrons around them in many of their compounds. Thus, the statement is false.
04

Statement (d)

Resonance structures are different ways of drawing the same molecule, acknowledging the fact that not all electrons are localized. They are not separable from one another. Therefore, this statement is also false.

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Most popular questions from this chapter

The formulas for the fluorides of the third-period elements are \(\mathrm{NaF}, \mathrm{MgF}_{2}, \mathrm{AlF}_{3}, \mathrm{SiF}_{4}, \mathrm{PF}_{5}, \mathrm{SF}_{6}\) and \(\mathrm{ClF}_{3}\). Classify these compounds as covalent or ionic.

Comment on the correctness of the statement, "All compounds containing a noble gas atom violate the octet rule."

What is bond enthalpy? Bond enthalpies of polyatomic molecules are average values, whereas those of diatomic molecules can be accurately determined. Why?

The octet rule applies mainly to the second-period elements. Explain.

Give three examples of compounds that do not satisfy the octet rule. Write a Lewis structure for each.
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