I have a hopefully simple question. I am a tutor working with a student that wants to know where to find the most recent accurate measurements for elemental properties. He's only in Chemistry I, so he's not looking for every property out there calculated multiple ways. I think he (and I) just like looking at the best sources. So we're looking for the following:

  1. Latent heat of fusion
  2. Latent heat of vaporization
  3. Melting point
  4. Boiling point
  5. Density
  6. Specific heat
  7. Ionization energy
  8. Atomic radius (metallic and covalent)
  9. Atomic mass
  10. Electronegativity
  11. Commonality and uncommonality of charges (like oxygen is commonly -2 but is also -1 in peroxide)

I can point him to wikipedia or https://ptable.com/#Properties/Series for some of the information, but I myself don't know where the most legitimate sources for these values can be found. My CRC handbook (97th edition) lists ionization energies, but for atomic weight it doesn't list the weight of the most common isotope of elements like Ac. Also, it's a few years old.

My question is, what are the current best sources of accurate values for each of these properties?

  • 2
    $\begingroup$ I don't you will find everything in one place. Have you explored the NIST website? They are supposed to have the most accurate/ or accepted values. Wikipedia for serious researchers should be their last resort but it is great starting place. The Landolt-Bornstein tables (partly in German) used to have tables of properties but they are not online completely. $\endgroup$
    – ACR
    Commented Jan 21, 2021 at 21:34
  • $\begingroup$ For #9, google for 'atomic mass evaluation 2016'. $\endgroup$
    – Jon Custer
    Commented Jan 21, 2021 at 22:02
  • $\begingroup$ @Farooq: You know I had trouble finding anything on NIST and then you're comment made me think to good NIST instead of searching their website. That works better. $\endgroup$
    – Jay
    Commented Jan 22, 2021 at 4:16
  • $\begingroup$ @Custer. That's a pretty cool reference. $\endgroup$
    – Jay
    Commented Jan 22, 2021 at 4:17
  • 1
    $\begingroup$ For the radioactive elements greater than uranium there are a couple of considerations. First all elements fermium and beyond the half life is so short that bulk measurements are probably not available. Also there is no natural source for anything greater than uranium so the isotope mix of any element with a greater atomic number would depend on how that element was synthesized and how long it had "cooled off" since its synthesis. $\endgroup$
    – MaxW
    Commented Jan 22, 2021 at 4:29

1 Answer 1


You should teach your student not to use numerical values with as many significant figures as possible. Knowing how to make sense to decimals is part of the scientific culture. The distance between two cities cannot be given to the least micrometer : it has no meaning. The weight of an object has no use if it is given such as $123,45678910111213 g$. The least figures which can be given for sure is the milligram (here 6). Put on a balance, such an object will display fluctuating next figures. Already the figure $7 (0.1 mg$) will fluctuate at the least draft. To be sure of the next decimals you must put your balance in an insulated and closed room without nobody entering during the whole day, in order to avoid drafts. And even, the least dust grain falling from the air will change one or two of the following figures. So please do learn to use numbers with maybe $2, 3, 4$ or $5$ significant figures. But not with ten or twenty significant figures. It is not the way science works. So why looking for the newest published values which have one or two more significant figures ? The given weight $123.45678910111213 g$ is not better than $123.456 g$. It only gives an irrational feeling of superiority. That's all. It has no meaning for usual applications. Nobody will believe you if you say that you have calculated a weight of $123.4567891011121314 g$, or measured a temperature of $12.3456789 °C$.

  • $\begingroup$ I'd quibble a bit. Physicists try to measure many values such as the fundamental constants with great precision. However in chemistry 4 significant figures would be more than sufficient for 99.99% of the work, and it would take really precise lab work to get 4 significant figures. $\endgroup$
    – MaxW
    Commented Jan 22, 2021 at 4:17
  • 1
    $\begingroup$ @MaxW It is not always what is sufficient, but also available. Physicists are often able to measure many things with high accuracy, or even predict them so ( like QED prediction of electron magnetic momentum with the accuracy of 11 digits ). OTOH, they are not so lucky with the gravitational constant. We chemists are often glad if we are able to get some data with 4 digits accuracy. E.g. the mean molar mass of elements with variable isotopic composition, or activities of ions in solutions. $\endgroup$
    – Poutnik
    Commented Jan 22, 2021 at 7:18
  • $\begingroup$ @Poutnik - Agree totally, but Maurice said "It is not the way science works." Physicists know mass of each isotope with astonishing accuracy. The limiting factor for atomic masses of course is the variation in isotope fractions across the planet. $\endgroup$
    – MaxW
    Commented Jan 22, 2021 at 7:24
  • 2
    $\begingroup$ @Maxw Sure. E.g. $\ce{M_\ce{Zn}}=\pu{65.38(2) g/mol}$ . Once I have read a quote of a famous chemist in some textbook in a sense like: "Nothing is better sign of chemical ignorance but untamed precission of calculations." All is about known or estimated accuracy of the input data and constants and about rules of error propagation. $\endgroup$
    – Poutnik
    Commented Jan 22, 2021 at 7:40
  • $\begingroup$ There's some misinformation and hyperbole in this post. Those who understand science won't be misled, but my concern is those who don't might be: (1) "The least figures which can be given for sure is the milligram". No, there are higher-precision enclosed balances. (2) "To be sure of the next decimals you must put your balance in an insulated and closed room without nobody entering during the whole day, in order to avoid drafts." No, you can certainly get beyond 1 mg without having to prevent anyone from entering the room "for a whole day" (!). $\endgroup$
    – theorist
    Commented Feb 21, 2021 at 2:57

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