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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asked Oct 21, 2023 at 3:24
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2$\begingroup$ 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. $\endgroup$– PoutnikCommented Oct 21, 2023 at 4:19
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$\begingroup$ See last paragraph of this answer: chemistry.stackexchange.com/a/91488/17368 $\endgroup$– Nilay GhoshCommented Oct 21, 2023 at 4:26
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$\begingroup$ @Poutnik Well said. Even Mn is prone to exception: chemistry.stackexchange.com/questions/39786/… $\endgroup$– Nilay GhoshCommented Oct 21, 2023 at 4:28
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$\begingroup$ 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 CusterCommented Oct 21, 2023 at 16:26
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1$\begingroup$ @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 $\endgroup$– PoutnikCommented Oct 23, 2023 at 15:36
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1 Answer
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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 -
answered Oct 23, 2023 at 15:00
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$\begingroup$ and regarding Technetium: The crystal structure of the bulk pure metal is hexagonal close-packed, and crystal structures of the nanodisperse pure metal are cubic. $\endgroup$ Commented Oct 24, 2023 at 2:19
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1$\begingroup$ @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. $\endgroup$ Commented Oct 24, 2023 at 15:11
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$\begingroup$ Tin transitions from the ductile white phase to brittle gray tin on cooling to about 13C. $\endgroup$ Commented Oct 24, 2023 at 23:15
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$\begingroup$ @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. $\endgroup$ Commented Oct 24, 2023 at 23:49