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Ethylene, C2H4, and tetrafluoroethylene, C2F4, are used to
Chapter 10, Problem 83P(choose chapter or problem)
Ethylene, \(\mathrm{C}_{2} \mathrm{H}_{4}\) , and tetrafluoroethylene, \(\mathrm{C}_2\mathrm{F}_4\) , are used to make the polymers polyethylene and polytetrafluoroethylene (Teflon), respectively.
(a) Draw the Lewis structures for \(\mathrm{C}_{2} \mathrm{H}_{4}\) and \(\mathrm{C}_2\mathrm{F}_4\) , and give the ideal \(\mathrm{H}-\mathrm{C}-\mathrm{H}\) and \(\mathrm{F}-\mathrm{C}-\mathrm{F}\) bond angles.
(b) The actual \(\mathrm{H}-\mathrm{C}-\mathrm{H}\) and \(\mathrm{F}-\mathrm{C}-\mathrm{F}\) bond angles are \(117.4^{\circ}\) and \(112.4^{\circ}\) , respectively. Explain these deviations.
Questions & Answers
QUESTION:
Ethylene, \(\mathrm{C}_{2} \mathrm{H}_{4}\) , and tetrafluoroethylene, \(\mathrm{C}_2\mathrm{F}_4\) , are used to make the polymers polyethylene and polytetrafluoroethylene (Teflon), respectively.
(a) Draw the Lewis structures for \(\mathrm{C}_{2} \mathrm{H}_{4}\) and \(\mathrm{C}_2\mathrm{F}_4\) , and give the ideal \(\mathrm{H}-\mathrm{C}-\mathrm{H}\) and \(\mathrm{F}-\mathrm{C}-\mathrm{F}\) bond angles.
(b) The actual \(\mathrm{H}-\mathrm{C}-\mathrm{H}\) and \(\mathrm{F}-\mathrm{C}-\mathrm{F}\) bond angles are \(117.4^{\circ}\) and \(112.4^{\circ}\) , respectively. Explain these deviations.
ANSWER:Step 1 of 4
(a) Here, we are going to draw the Lewis structures for and
, and give the ideal H—C—H and F—C—F bond angles.
For determining the bond angles, we have to determine the molecular shape of the molecule by using VSEPR theory.
The valence-shell electron-pair repulsion (VSEPR) theory is based on the electron groups around the central atom.
An electron group can be an electron pair, a lone pair, a single unpaired electron, a double bond or a triple bond on the center atom. VSEPR theory can help to predict the shape of a molecule.
According to VSEPR theory,
(a) The geometry of a molecule is determined by the number of electron groups on the central atom.
(b) The number of electron groups is determined from the Lewis structure of the molecule.
(c) The geometry of the electron groups is determined by their repulsions
Lone pair–lone pair > lone pair–bonding pair > bonding pair–bonding pair
(d) The bond angles vary in the presence of double and triple bond due to their higher occupancy than single bonds. Similarly, the presence lone pair make the bond angle smaller than the presence of double bond.