1. Which of the following species has the longest N—O bond? NO3 NO+ NO2− H2NOH

Best Lewis Formula and Molecular Geometry A student writes the Lewis electron-dot formula for the carbonate anion, CO32, as a Does this Lewis formula obey the octet rule? Explain. What are the formal charges on the atoms? Try describing the bonding for this formula in valence bond terms. Do you have any difficulty doing this? b Does this Lewis formula give a reasonable description of the electron structure, or is there a better one? If there is a better Lewis formula, write it down and explain why it is better. c The same student writes the following resonance description for CO2: Is there something wrong with this description? (What would you predict as the geometries of these formulas?) d Is one or the other formula a better description? Could a value for the dipole moment help you decide? e Can you write a Lewis formula that gives an even better description of CO2? Explain your answer.

a Carbonyl fluoride, COF2, is an extremely poisonous gas used in organofluorine synthesis. Give the valence bond description of the carbonyl fluoride molecule. (Both fluorine atoms are attached to the carbon atom.) b Nitrogen, N2, makes up about 80% of the earths atmosphere. Give the valence bond description of this molecule.

Formamide, HC(O)NH2, is prepared at high pressures from carbon monoxide and ammonia, and serves as an industrial solvent (the parentheses around the O indicate that it is bonded only to the carbon atom and that the carbon atom is also bonded to the H and the N atoms). Two resonance forms (one with formal charges) can be written for formamide. Write both resonance structures, and predict the bond angles about the carbon and nitrogen atoms for each resonance form. Are they the same? Describe how the experimental determination of the HNH bond angle could be used to indicate which resonance form is more important.

Put the following three molecules in order of increasing H-X-H bond angle, where X is the central atom. CH4 H2S PH3 A. CH4 < H2S < PH3 B. H2S < PH3 < CH4 C. CH4 < PH3 < H2S D. H2S < CH4 < PH3 E. PH3 < CH4 < H2S く く

For each compound in the table below, decide whether there would be any hydrogen-bonding force between molecules of the compound, or between molecules of the compound and molecules of water. name acetic acid dimethyl ether compound hypobromous acid formula or Lewis structure H :0: H-C-C-O-H H H H-C-0-C H H H T HBrO | H Between molecules of the compound? yes O O no O yes no yes hydrogen-bonding force no Between molecules of the compound and molecules of water? O O yes no yes no yes no X

As you go from HF to HI, does the H—X bond become moreor less polar?

The caffeine molecule is shown below. Indicate the electron geometry AND the molecular shape around each of the indicated atoms (six answers in total). Be aware that the angles may not be drawn correctly in this Lewis structure.

A chemist wants to observe the following reaction: 2H2 + O2 → 2H2O The chemist is standing inside a room with oxygen in the air and has a balloon filled with hydrogen. The chemist holds a small flame up to the hydrogen balloon. When the balloon pops, the hydrogen explodes in a ball of fire. Based on what you know about breaking and forming bonds, explain which part of the reaction is higher in energy (i.e., does it take more energy to break the bonds of the reactants, or is more energy given off when the product bonds are formed?). Defend your answer in three to five sentences.