14.1 More Structures & Shapes

But-2-ene-1,4-dioic acid exists as both cis and trans isomers. The cis isomer is shown below

Describe the type of covalent bond between carbon and hydrogen in the molecule shown above and how it is formed.

Identify how many sigma bonds and how many pi (π) bonds are present in cis but-2-ene-1,4-dioc acid.

Draw the Lewis structures, predict the shape and deduce the bond angles for xenon tetrafluoride.

Compare the polarity of xenon tetrafluoride with chlorine trifluoride.

Carbon dioxide can be represented by at least two resonance structures, I and II.

Calculate the formal charge on each oxygen atom in the two structures.

Structure	I	II
O atom labelled (1)
O atom labelled (2)

Deduce, giving a reason, the more likely resonance structure from part a)

Nitrous oxide can be represented by different Lewis (electron dot) structures. 

Deduce the formal charge (FC) of the nitrogen and oxygen atoms in three of these Lewis (electron dot) structures, A, B and C, represented below. 

LHS: atom on the left-hand side; RHS: atom on the right-hand side

	Lewis (electron dot) structure	FC of O on LHS	FC of central N	FC of N on RHS
A
B
C

Based on the formal charges assigned in part c), deduce which Lewis (electron dot) structure of N₂O (A, B, or C) is the preferred.

Explain another factor that also must be taken into account in determining the preferred structure.

Use the concept of formal charge to explain why BF₃ is an exception to the octet rule.

Compounds containing two different halogen atoms bonded together are called interhalogen compounds. They are interesting because they contain halogen atoms in unusual oxidation states. One such compound is BrF₃. 

Deduce the electron domain geometry and molecular geometry of BrF₃.

Give the approximate bond angle(s) and a valid Lewis (electron dot) structure for BrF₃. 

Explain why bromine trifluoride, BrF₃ has its lone pairs of electrons located in equatorial positions. 

Draw two different Lewis (electron dot) structures for SO₄^2–, one of which obeys the octet rule for all its atoms, the other which has an octet for S expanded to 12 electrons. 

Explain which of the two SO₄^2– structures is preferred using formal charges.

Consider the molecule shown below.

  Identify the number of sigma and pi bonds in this molecule.

One of the intermediates in the reaction between nitrogen monoxide and hydrogen is dinitrogen monoxide, N₂O. This can be represented by the resonance structures below

 Analyse the bonding in dinitrogen monoxide in terms of sigma and pi bonds.