Element: Osmium

General data

Element name	Osmium
Chemical symbol	Os
Atomic number Z	76
Year discovered	1803
Standard state (25°C)	Solid
Category	Transition metal
Block	d
Atomic mass	190.23
CPK color	#266696

Physical properties

Melting point	3306 K (3033 °C)
Boiling point	5285 K (5012 °C)
Density	22.57 g/cm³

Energy properties

First ionization energy	8.7 eV
Electron affinity	1.1 eV

Atomic structure

Protons	76 (Atomic number)
Neutrons (Os-192, most abundant isotope)	116
Electrons	76
Electron configuration	[Xe] 6s² 4f¹⁴ 5d⁶
Oxidation states	+4, +3
Electronegativity (Pauling)	2.2
Atomic radius (van der Waals)	216 pm

Ionization energies - NIST ASD (76 states)

State	Charge	Ioniz. energy (eV)	Type
Os I	0+	8.43823 ± 0.0002	measured
Os II	1+	17 ± 1	semi-empirical
Os III	2+	25 ± 1.6	calculated
Os IV	3+	41 ± 1.7	calculated
Os V	4+	55 ± 1.9	calculated
Os VI	5+	70.1 ± 2	calculated
Os VII	6+	85.1 ± 2	calculated
Os VIII	7+	102.02 ± 0.07	semi-empirical
Os IX	8+	168.7 ± 0.5	semi-empirical
Os X	9+	190 ± 10	calculated
Os XI	10+	213 ± 11	calculated
Os XII	11+	235 ± 12	calculated
Os XIII	12+	269 ± 14	calculated
Os XIV	13+	298 ± 15	calculated
Os XV	14+	322 ± 16	calculated
Os XVI	15+	367 ± 19	calculated
Os XVII	16+	410 ± 21	calculated
Os XVIII	17+	436 ± 22	calculated
Os XIX	18+	470 ± 24	calculated
Os XX	19+	520 ± 30	calculated
Os XXI	20+	570 ± 30	calculated
Os XXII	21+	620 ± 30	calculated
Os XXIII	22+	670 ± 30	calculated
Os XXIV	23+	720 ± 40	calculated
Os XXV	24+	770 ± 40	calculated
Os XXVI	25+	820 ± 40	calculated
Os XXVII	26+	870 ± 40	calculated
Os XXVIII	27+	920 ± 50	calculated
Os XXIX	28+	970 ± 50	calculated
Os XXX	29+	1015 ± 25	calculated
Os XXXI	30+	1262 ± 4	calculated
Os XXXII	31+	1311 ± 4	calculated
Os XXXIII	32+	1364 ± 4	calculated
Os XXXIV	33+	1420 ± 5	calculated
Os XXXV	34+	1474 ± 5	calculated
Os XXXVI	35+	1528 ± 5	calculated
Os XXXVII	36+	1606 ± 5	calculated
Os XXXVIII	37+	1660 ± 4	calculated
Os XXXIX	38+	1720 ± 4	calculated
Os XL	39+	1776 ± 4	calculated
Os XLI	40+	1996 ± 4	calculated
Os XLII	41+	2052 ± 4	calculated
Os XLIII	42+	2112 ± 4	calculated
Os XLIV	43+	2168 ± 4	calculated
Os XLV	44+	2336 ± 4	calculated
Os XLVI	45+	2400 ± 4	calculated
Os XLVII	46+	2552 ± 4	calculated
Os XLVIII	47+	2615.5 ± 1.4	semi-empirical
Os XLIX	48+	4374 ± 4	calculated
Os L	49+	4501 ± 4	calculated
Os LI	50+	4635 ± 4	calculated
Os LII	51+	4779 ± 4	calculated
Os LIII	52+	4917 ± 4	calculated
Os LIV	53+	5052 ± 5	calculated
Os LV	54+	5280 ± 5	calculated
Os LVI	55+	5421 ± 5	calculated
Os LVII	56+	5575 ± 5	calculated
Os LVIII	57+	5717 ± 6	calculated
Os LIX	58+	6115 ± 6	calculated
Os LX	59+	6240 ± 7	calculated
Os LXI	60+	6376 ± 10	calculated
Os LXII	61+	6503 ± 12	calculated
Os LXIII	62+	7039 ± 15	calculated
Os LXIV	63+	7185 ± 19	calculated
Os LXV	64+	7468 ± 24	calculated
Os LXVI	65+	7610 ± 30	calculated
Os LXVII	66+	16560 ± 40	calculated
Os LXVIII	67+	16900 ± 40	calculated
Os LXIX	68+	17270 ± 50	calculated
Os LXX	69+	17620 ± 50	calculated
Os LXXI	70+	19600 ± 60	calculated
Os LXXII	71+	20030 ± 60	calculated
Os LXXIII	72+	20570 ± 70	calculated
Os LXXIV	73+	20920.6 ± 0.22	calculated
Os LXXV	74+	83976.18 ± 0.22	calculated
Os LXXVI	75+	85614.42 ± 0.15	calculated

Value type as given by NIST ASD: measured - from evaluated experimental data; calculated - from ab initio calculations (mostly highly ionised atoms that have not been measured; for the simplest ones, e.g. H I, the calculation is more accurate than measurement); semi-empirical - from interpolation, extrapolation or another semi-empirical method.

Photos

Photo of the element: Osmium (Os) — © images-of-elements.com (CC BY 3.0)

Isotopes (43)

A	N	Half-life	Decay
Os-161	85	0.64 ms	α
Os-162	86	2.1 ms	α
Os-163	87	5.8 ms	α
Os-164	88	21 ms	α
Os-165	89	71 ms	α
Os-166	90	212 ms	α
Os-167	91	839 ms	α
Os-168	92	2.1 s	α
Os-169	93	3.4 s	α
Os-170	94	7.4 s	EC/β⁺
Os-171	95	8.3 s	EC/β⁺
Os-172	96	19.2 s	EC/β⁺
Os-173	97	22.4 s	EC/β⁺
Os-174	98	44 s	EC/β⁺
Os-175	99	1.4 min	EC/β⁺
Os-176	100	3.6 min	EC/β⁺
Os-177	101	3.0 min	EC/β⁺
Os-178	102	5.0 min	EC/β⁺
Os-179	103	6.3 min	EC/β⁺
Os-180	104	21.5 min	EC/β⁺
Os-181	105	106 min	EC/β⁺
Os-182	106	22.04 h	EC
Os-183	107	13.0 h	EC/β⁺
Os-184	108	1.12×10¹³ a	α
Os-185	109	92.95 d	EC
Os-186	110	2.0×10¹⁵ a	α
Os-187	111	stable	-
Os-188	112	stable	-
Os-189	113	stable	-
Os-190	114	stable	-
Os-191	115	15.00 d	β⁻
Os-192	116	stable	-
Os-193	117	29.830 h	β⁻
Os-194	118	6.0 a	β⁻
Os-195	119	6.4 min	β⁻
Os-196	120	34.9 min	β⁻
Os-197	121	93 s	β⁻
Os-198	122	130 s	β⁻
Os-199	123	5 s	β⁻
Os-200	124	6 s	β⁻
Os-201	125	unknown	β⁻
Os-202	126	unknown	β⁻
Os-203	127	unknown	β⁻

Data sources

PubChem Periodic Table API - Retrieved on 29 June 2026 - licence: CC0
IUPAC CIAAW - Abridged Standard Atomic Weights 2024 - Table version: 2024 - licence: Public domain
NNDC Wallet Cards 2023 - Data as of 15 October 2024 - licence: Public domain
Images of Elements - Retrieved on 29 June 2026 - licence: CC BY 3.0

More about the data sources