Issue Date: January 21, 2008
Fred Zoepfl's letter to the editor (C&EN, Nov. 12, 2007, page 10), pointed out that the boiling point of gallium is stated incorrectly in an earlier C&EN article (Sept. 24, 2007, page 107) about the talk on "Inorganic 'Jeopardy'" that I gave at the ACS national meeting in Boston. Zoepfl notes that his CRC Handbook (86th Ed.) gives a value of 2,204 °C for the boiling point of gallium. I own the 64th edition of the CRC and upon checking it I found a gallium boiling point value of 2,403 °C (page B-93). So, did the boiling point of gallium drop by 199 °C in the years between the 64th edition (dated 1983-84) and the 86th edition? I also own the 44th edition of the CRC (published in 1962), which lists a boiling point of 1,983 °C for gallium.
The textbook my students use to prepare for their weekly "Jeopardy" quizzes, D. A. McQuarrie and P. A. Rock, "Descriptive Chemistry," (W. H. Freeman, 1985), shows a gallium boiling point of 2,250 °C. That is the value I expect my students to be familiar with and that I accept as the correct answer on my "Jeopardy" quizzes.
I am not in the habit of double-checking every physical constant listed in every textbook for the courses I teach, and I certainly don't go into the lab to verify published values by measuring them myself. If I did either of those things, I fear I would get nothing else done and would have left the profession years ago. Nevertheless, inspired by Zoepfl's letter to the editor, I checked three other sources that are generally regarded as authoritative. F. A. Cotton et al., "Advanced Inorganic Chemistry," 6th edition (John Wiley & Sons, 1999), lists the boiling point as "~2,250 °C". This is the same value as that found in McQuarrie & Rock, which omits the "~". N. N. Greenwood and A. Earnshaw, "Chemistry of the Elements" (Pergamon Press, 1984), lists a gallium boiling point of 2,403 °C. The National Institute of Standards & Technology database (webbook.nist.gov) lists a gallium boiling point of 2,676 K, or 2,403 °C, in agreement with both the 64th edition CRC and Greenwood & Earnshaw.
I agree with Zoepfl's assertion that cerium has a wider liquid range than gallium. However, the students' textbook for the "Jeopardy" quizzes does not cover the lanthanides or actinides, so I do not think it would be fair to expect them to know anything about the chemical or physical properties of cerium.
J. Van Houten
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