Transition element

(Under construction)

A transition element is a chemical element element whose atomic electron configuration of the ground (lowest energy) state has an incompletely filled d sub-shell. The electron configuration contains (nd)^k, with 1 ≤ k ≤ 9, and where n is a principal quantum number. The unpaired valence d electrons give rise to some characteristic magnetic properties of (compounds of) transition metals.

Also the atoms copper (Cu), silver (Ag), and gold (Au) that have a filled d sub-shell, but after ionization have an incomplete d sub-shell, are usually seen as transition elements. They have the lowest energy configuration (np)⁶(nd)¹⁰(n+1)s, with n = 3, 4, and 5 for copper, silver, and gold, respectively.

In the past the group 12 elements zinc (Zn), cadmium (Cd), and mercury (Hg), that are included in the "d-block" of the periodic table, were seen as transition elements, but they are nowadays rarely considered as such, because they lack some characteristic magnetic properties.

A strict application of the definition would describe lutetium (Lu) as a transition element as it has a singly occupied 5d orbital in its ground state, but it is a lanthanoid (previously known as lanthanide) according to IUPAC. It appears most commonly as a positive ion without d-electrons in the valence shell and without characteristic magnetic properties. For the same reason scandium (Sc) and yttrium (Y) are often omitted from the list of transition metals.

The naturally occurring transition elements are shown in two tables. The elements in Period 7, although formally transition elements, are man-made [except for Actinium (Z = 87)] and are not shown.

Rows and columns of the Periodic Table of Elements containing transition elements
The atomic number Z is between brackets

Group	3	4	5	6	7	8	9	10	11
Period 4	Sc (21)	Ti (22)	V (23)	Cr (24)	Mn (25)	Fe (26)	Co (27)	Ni (28)	Cu (29)
Period 5	Y (39)	Zr (40)	Nb (41)	Mo (42)	Tc (43)	Ru (44)	Rh (45)	Pd (46)	Ag (47)
Period 6	La (57)	Hf (72)	Ta (73)	W (74)	Re (75)	Os (76)	Ir (77)	Pt (78)	Au (79)

Reference

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Atomic Electron Configurations of Transition Elements

Z	Symbol	Element	Core	Configuration
21	Sc	Scandium	[Ar]	(3d)1 (4s)2
22	Ti	Titanium	[Ar]	(3d)2 (4s)2
23	V	Vanadium	[Ar]	(3d)3 (4s)2
24	Cr	Chromium	[Ar]	(3d)5 (4s)1
25	Mn	Manganese	[Ar]	(3d)5 (4s)2
26	Fe	Iron	[Ar]	(3d)6 (4s)2
27	Co	Cobalt	[Ar]	(3d)7 (4s)2
28	Ni	Nickel	[Ar]	(3d)8 (4s)2
29	Cu	Copper	[Ar]	(3d)10(4s)1
39	Y	Yttrium	[Kr]	(4d)1 (5s)2
40	Zr	Zirconium	[Kr]	(4d)2 (5s)2
41	Nb	Niobium	[Kr]	(4d)4 (5s)1
42	Mo	Molybdenum	[Kr]	(4d)5 (5s)1
43	Tc	Technetium	[Kr]	(4d)6 (5s)1
44	Ru	Ruthenium	[Kr]	(4d)7 (5s)1
45	Rh	Rhodium	[Kr]	(4d)8 (5s)1
46	Pd	Palladium	[Kr]	(4d)10(5s)
47	Ag	Silver	[Kr]	(4d)10(5s)1
57	La	Lanthanum	[Xe]	(5d)1 (6s)2
72	Hf	Hafnium	[Xe*]	(5d)2 (6s)2
73	Ta	Tantalum	[Xe*]	(5d)3 (6s)2
74	W	Tungsten	[Xe*]	(5d)4 (6s)2
75	Re	Rhenium	[Xe*]	(5d)5 (6s)2
76	Os	Osmium	[Xe*]	(5d)6 (6s)2
77	Ir	Iridium	[Xe*]	(5d)7 (6s)2
78	Pt	Platinum	[Xe*]	(5d)9 (6s)1
79	Au	Gold	[Xe*]	(5d)10(6s)1

[Ar] stands for:   (1s)²(2s)²(2p)⁶ (3s)²(3p)⁶
[Kr] stands for:   [Ar](3d)¹⁰(4s)²(4p)⁶
[Xe] stands for:   [Kr](5s)²(5p)⁶
[Xe*] stands for:   [Xe](4f)¹⁴