Problem Set for CHEM422 Inorganic Chemistry
The Evolution of Bonding Theory

Question 1

The dualistic theory formulated by Berzelius was rather successful in describing inorganic compounds such as MgSO₄ and Na₂CO₃, but not organic compounds such as C₆H₆ and C₂H₅OH. Today we distinguish two kinds of bonding — ionic and covalent . What type is more important for minerals? What about organic compounds? Why did Berzelius's electrochemical theory work so much better for minerals than for organic compounds?

Question 2

Another problem with radical theory is its ambiguity. There are two radicals that, when combined with elements or simple compounds, will produce the compounds below. What are these two radicals?

nitric ether C₂H₅NO₂

ethyl chloride C₂H₅Cl

ethyl cyanide C2H₅CN

Question 3

Reminders of the dualistic and radical theories remain with us today. In organic chemistry, compounds are often written with the symbol R, signifying a hydrocarbon group ( CH₃–, C₂H₅–, etc.). For instance, a compound with the -OH functional group is called an "alcohol." A set of alcohols can be represented as R–OH , for CH₃–OH, C₂H₅–OH, etc. From what word is the symbol "R" derived?

Question 4

Fertilizers are labeled with three numbers: 20–10–5, for instance. These numbers represent the percent N, P₂O₅, and K₂O in the fertilizer. Expressing phosphorus and potassium as oxides is a vestige of one of the early theories that was popular with mineralogists. Do you think this stems from dualistic, radical, or valence theory? Why?

Question 5

Kekulé, because of the success of tetravalent carbon inorganic chemistry, felt strongly that the valence of every element was constant. One problem faced by any theory that requires constant valence is the existence of pairs of compounds such as PCl₃ and PCl₅. Rather than assigning two valences (3 and 5) to phosphorus, in 1864 Kekulé suggested that there were "atomic compounds" with saturated valences (PCl₃) and "molecular compounds" formed as combinations of two different molecules (PCl₅ = PCl₃ • Cl₂). Thinking about the older theories (dualistic and radical) in this simulation, to what theory do Kekulé's molecular compounds seem to be related? In science courses, we tend to portray scientific progress as a straight-line path with no backtracking or blind alleys. What does the example of Kekulé's molecular compounds suggest about this point of view?

Question 6

The change from a dualistic paradigm (Berzelius —> radicals) to a unitary paradigm based on valences (Dumas —> Gerhardt —> Kekulé) can be thought of as a scientific revolution. Given the information from this simulation, how well does Kuhn's picture fit? When you answer this question, be as specific as you can, citing examples from the history of this period. For instance, does Berzelius's reaction to the unitary paradigm fit Thomas Kuhn's model?

Question 7

Write two different structural formulas for C₄H₁₀.

Hint: look for different ways of connecting the carbon atoms. The different forms are called "structural isomers."

Question 8

Chemistry in the 19th century was in a muddled state with uncertain or inaccurate atomic weights and fuzzy ideas about chemical combination (atoms and molecules were not always distinguished).

You know that calcium reacts with 32 g of oxygen gas to form 112 g of solid calcium oxide.

If you think that oxygen gas is O₂ and that the formula of calcium oxide is CaO₂, then what will be your estimate of the atomic weight of calcium? The atomic weight of O is 16.

Question 9

Chemistry in the 19th century was in a muddled state with uncertain or inaccurate atomic weights and fuzzy ideas about chemical combination (atoms and molecules were not always distinguished).

You know that calcium reacts with 32 g of oxygen gas to form 112 g of solid calcium oxide.

If you think that oxygen gas is monatomic (O), so that its atomic weight is 32, and that the formula of calcium oxide is CaO, what will be your estimate of the atomic weight of calcium?

Question 10

The organic chemistry section of your text discusses functional groups. Two compounds that were important in the overthrow of the Radical Theory were CH₃COOH and CCl₃COOH, both of which have the same functional group. What is the name of this functional group? –COOH is the symbol for the

–C–OH group.
.||
.O

Werner-Jorgensen Controversy

Question 1

What led Werner to question the chain theory? Was it making erroneous predictions or was it not explaining an observation he finds significant?

Question 2

What is Jorgensen's objection to the new theory?

Question 3

A nitrogen atom with 5 bonds (–NH₃–) in a chain structure would bother modern chemists, but was reasonable in the 19th century. Considering NH₄Cl, chemists of that era concluded that nitrogen can have a valence of 5. Thinking about modern Lewis structures, how many bonds does nitrogen usually form? Today we know about both covalent and ionic bonds. What is the bonding like in NH₄Cl?

Question 4

Werner identified two types of valences in his structures. For instance, in Co(NH₃)₆Cl₃, the secondary valence is satisfied by the ammonia groups, which are held to the cobalt and do not form ions when the compound dissolves in water. The chlorines, which satisfy the primary valence, are easily removed and form insoluble silver compounds if silver nitrate is added. Think about ionic and covalent bonding. How would you explain these two types of valences using modern bonding theory?

Question 5

Many compounds are hydrated. Their formulas are written in a way that is a throwback to the days of dualism — CoCl₂ • 6 H₂O, for instance. How would you explain the structure of this hydrate using Werner's coordination theory?

Question 6

Which scientist does the conductivity evidence lead you to support — Werner, Jorgensen, or neither. Explain why.

Question 7

Which scientist does the isomers evidence lead you to support — Werner, Jorgensen, or neither. Explain why.

Question 8

Consider the two structures below for the metal ammine, Co(NH₃)₃(NO₂)₂Cl.

Emil Peterson (Z. Phys. Chem. 1897, 22, 410) found the conductivity of this compound to be 116. Which of the two structures above does this experimental value support? How would Werner explain this?

Question 9

Kauffman (2) mentions Ostwald's twofold division of scientific genius.

Do Werner and Jorgensen fit into this scheme? If you think so, explain why.

Question 10

The period between 1893 and 1907 was a revolutionary time in the field of inorganic chemistry. Look back at the description of Thomas Kuhn's picture of scientific revolutions. Discuss how Kuhn's portrayal of scientific change applies to the Werner-Jorgensen controversy. You might compare it to the dualism-unitary revolution, which we saw in the Evolution of Bonding Theory simulation. Does a crisis precede the introduction of the new paradigm in both cases? How is Jorgensen's response different from that of Berzelius? The ideal scientist is unbiased, devoted to the truth, and willing to change if his or her ideas do not stand up in the long run in the broader scientific community (3). In the conflicts involving their theories, does Berzelius or Jorgensen fit this idealized picture better?