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Chapter 8: Problem 65

In the vapor phase, \(\mathrm{BeCl}_{2}\) exists as a discrete molecule. (a) Draw the Lewis structure of this molecule, using onlysingle bonds. Does this Lewis structure satisfy the octet rule? (b) What other resonance structures are possible that satisfy the octet rule? (c) On the basis of the formal charges, which Lewis structure is expected to be dominant for \(\mathrm{BeCl}_{2} ?\)

Short Answer

Expert verified
The initial Lewis structure of BeCl2 is: ``` Cl | Be | Cl ``` This structure does not satisfy the octet rule due to Be having only 4 electrons in its outer shell. Despite this, there are no other resonance structures that satisfy the octet rule for BeCl2. Considering the formal charges, the given BeCl2 Lewis structure is dominant since all atoms have a formal charge of 0, providing stability.

Step by step solution

01

Draw the initial Lewis structure of BeCl2

To draw the Lewis structure of BeCl2, first find the total number of valence electrons in the molecule. Beryllium has 2 valence electrons, and each chlorine atom has 7 valence electrons. Therefore, there are a total of 2 + (2 x 7) = 16 valence electrons in the molecule. Now arrange Be in the center and form single bonds with the two Cl atoms. Finally, complete the octets of the chlorine atoms using the remaining electrons. BeCl2: ``` Cl | Be | Cl ``` Each chlorine atom has 8 electrons around it (2 from the bond with Be and 6 non-bonding electrons), while there are only 4 electrons around Be (2 from each bond).
02

Check if BeCl2 Lewis structure satisfies the octet rule

The octet rule states that atoms tend to gain, lose or share electrons to have 8 electrons in their outermost shell. The Lewis structure of BeCl2 does not satisfy the octet rule, as Be has only 4 electrons (2 from each bond with Cl) in its outer shell. Chlorine atoms in the molecule do satisfy the octet rule.
03

Find possible resonance structures

Since Be does not achieve an octet in the BeCl2 Lewis structure, we need to look for other possible resonance structures that satisfy the octet rule. However, there are no other resonance structures that satisfy the octet rule, because the beryllium atom can only form two bonds due to its low number of valence electrons.
04

Determine the dominant Lewis structure based on formal charge

We can now compare the formal charges of the atoms in the structure. Formal charge is calculated by: Formal Charge = (valence electrons) - (non-bonding electrons) - (1/2 x bonding electrons) When we check the given BeCl2 Lewis structure, it can be seen that the Be atom has a formal charge of 0 and the Cl atoms have a formal charge of 0. Since we do not have multiple structures with different charge distributions, the given BeCl2 Lewis structure is considered the dominant structure despite not following the octet rule. This is because of the stability provided by the formal charges being all equal to zero.

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Most popular questions from this chapter

Which ionic compound is expected to form from combining the following pairs of elements: (a) barium and fluorine, (b) cesium and chlorine, (c) lithium and nitrogen, (d) aluminum and oxygen?

Draw the Lewis structures for each of the following ions or molecules. Identify those that do not obey the octet rule, and explain why they do not: (a) \(\mathrm{SO}_{3}^{2-}\), (b) \(\mathrm{AlH}_{3}\) (c) \(\mathrm{N}_{3}^{-}\) (d) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) (e) \(\mathrm{SbF}_{5}\)

Based on Lewis structures, predict the ordering of \(\mathrm{N}-\mathrm{O}\) bond lengths in \(\mathrm{NO}^{+}, \mathrm{NO}_{2}^{-},\) and \(\mathrm{NO}_{3}^{-}\).

For elements in the third row of the periodic table and beyond, the octet rule is often not obeyed. What factors are usually cited to explain this fact?

Average bond enthalpies are generally defined for gas-phase molecules. Many substances are liquids in their standard state. coo (Section 5.7) By using appropriate thermochemical data from Appendix C, calculate average bond enthalpies in the liquid state for the following bonds, and compare these values to the gas-phase values given in Table 8.4: (a) \(\mathrm{Br}-\mathrm{Br}\), from \(\mathrm{Br}_{2}(l) ;\) (b) \(\mathrm{C}-\mathrm{Cl},\) from \(\mathrm{CCl}_{4}(l) ;\) (c) \(\mathrm{O}-\mathrm{O},\) from \(\mathrm{H}_{2} \mathrm{O}_{2}(I)\) (assume that the \(\mathrm{O}-\mathrm{H}\) bond enthalpy is the same as in the gas phase). (d) What can you conclude about the process of breaking bonds in the liquid as compared to the gas phase? Explain the difference in the \(\Delta H\) values between the two phases.
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