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It's been given in my book, that "With the exceptions of Zn, Cd, Hg and Mn, they have one or more typical metallic structures at normal temperatures." But, why this exception?

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    $\begingroup$ Exceptions are the rule in chemistry. There must be reason not to have them. Except for Mn, all 3 have fully filled d orbitals, like no other d block metal. Mn has it at least fully filled. Hg is liquid, so obviously just 1 form. BTW, the textbook statement has more possible interpretations. $\endgroup$
    – Poutnik
    Oct 21, 2023 at 4:19
  • $\begingroup$ See last paragraph of this answer: chemistry.stackexchange.com/a/91488/17368 $\endgroup$ Oct 21, 2023 at 4:26
  • $\begingroup$ @Poutnik Well said. Even Mn is prone to exception: chemistry.stackexchange.com/questions/39786/… $\endgroup$ Oct 21, 2023 at 4:28
  • $\begingroup$ Manganese has 4 allotropes between room temperature and the melting point. And it isn’t like any of the others have phase transitions particularly near room temperature. $\endgroup$
    – Jon Custer
    Oct 21, 2023 at 16:26
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    $\begingroup$ @IanBush Well, obviously there are rules and obviously there are exceptions of the rules. Therefore, liquids have obviously 1 phase, except obvious cases they have more :-P $\endgroup$
    – Poutnik
    Oct 23, 2023 at 15:36

1 Answer 1

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I challenge the basis for the textbook's statement.

Below I give a table of of the 31 elements in the middle sections of a standard periodic table, with information pulled from A.T. Dinsdale's SGTE Data for Pure Elements that is commonly used for thermodynamic modeling. One can quibble about Lanthanum vs Cerium so I included both. The table lists the element, the stable crystal structures at standard pressure, and the transition temperature from one crystal phase to the next, or to the liquid.

There are very few transitions between crystal structures at "normal" temperatures. Lanthanum goes from DHCP to FCC at 550K as the lowest temperature crystal-crystal phase transition. Cobalt going from HCP to FCC at 694K is next. Then Manganese going from CBCC to CUB at 980K.

Nineteen of the 31 elements listed have only one stable crystal phase at standard pressure. That is, the exhibit only a phase change to the liquid (i.e. melting).

I don't know about you, but none of those transitions is at a "normally" human experienced temperature.

Element Crystal   Transition
        Structure Temperature(K)
Sc        HCP     1608
          BCC     1814
Ti        HCP     1155
          BCC     1941
V         BCC     2183
Cr        BCC     2180
Mn        CBCC     980
          CUB     1360
          FCC     1411
          BCC     1519
Fe        BCC     1184
          FCC     1667
          BCC     1810
Co        HCP      694
          FCC     1768
Ni        FCC     1728
Cu        FCC     1357
Zn        HCP      692
Y         HCP     1751
          BCC     1795
Zr        HCP     1138
          BCC     2127
Nb        BCC     2750
Mo        BCC     2896
Tc       (HCP)    -
Ru        HCP     2607
Rh        FCC     2237
Pd        FCC     1828
Ag        FCC     1234
Cd        HCP      594
Ce        FCC     1000
          BCC     1072
La        DHCP     550
          FCC     1134
          BCC     1193
Hf        HCP     2016
          BCC     2506
Ta        BCC     3290
W         BCC     3694
Re        HCP     3458
Os        HCP     3306
Ir        FCC     2719
Pt        FCC     2041
Au        FCC     1337
Hg        Liquid  -
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  • $\begingroup$ @NilayGhosh - done. Technetium is not a common binary alloy component, so while there is some thermodynamic data available it was not included in the compilation above. Apparently the high pressure phase is tetragonal. $\endgroup$
    – Jon Custer
    Oct 24, 2023 at 15:11
  • $\begingroup$ Tin transitions from the ductile white phase to brittle gray tin on cooling to about 13C. $\endgroup$ Oct 24, 2023 at 23:15
  • $\begingroup$ @OscarLanzi - that is true, but it is below 25C that is considered the normal reference state. The thermodynamic data for the beta phase of tin is included in that compilation. $\endgroup$
    – Jon Custer
    Oct 24, 2023 at 23:49

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