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, n = 3, 4, 5. The incomplete electronic d subshell gives rise to some characteristic magnetic properties and brightly colored solutions of transition metal complexes.

Although the atoms copper (Cu), silver (Ag), and gold (Au) have in their lowest energy state a filled d sub-shell, after ionization (loss of one or more electrons) they obtain an incomplete d sub-shell; hence, they are usually seen as transition elements. As seen in the table of electron configurations below, Cu, Ag, and Au have the outer configuration: (nd)¹⁰(n+1)s¹, 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, have often been considered as transition elements, but they are nowadays rarely considered as such, because their compounds lack some of the characteristic 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 according to IUPAC it is a lanthanoid (previously known as lanthanide). It appears most commonly as a positive ion without d-electrons in the valence shell and without the characteristic properties of a transition element. For the same reason scandium (Sc) and yttrium (Y) are often omitted from the list of transition metals.

The first three series of the transition elements are shown in the two tables. The elements in the fourth series (period 7 of the periodic table), are formally transition elements. They are man-made [except for Actinium (Z = 87)], not much is known about their compounds and accordingly they are not shown in the tables.

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
1st series	Sc (21)	Ti (22)	V (23)	Cr (24)	Mn (25)	Fe (26)	Co (27)	Ni (28)	Cu (29)
2nd series	Y (39)	Zr (40)	Nb (41)	Mo (42)	Tc (43)	Ru (44)	Rh (45)	Pd (46)	Ag (47)
3rd series	La (57)	Hf (72)	Ta (73)	W (74)	Re (75)	Os (76)	Ir (77)	Pt (78)	Au (79)

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
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	[18 electrons].
[Kr] stands for:	[Ar](3d)10(4s)2(4p)6	[36 electrons].
[Xe] stands for:	[Kr](4d)10(5s)2(5p)6	[54 electrons].
[Xe*] stands for:	[Xe](4f)14	[68 electrons].