Element: Molybdenum

General data

Element name	Molybdenum
Chemical symbol	Mo
Atomic number Z	42
Year discovered	1778
Standard state (25°C)	Solid
Category	Transition metal
Block	d
Atomic mass	95.95
CPK color	#54B5B5

Physical properties

Melting point	2896 K (2623 °C)
Boiling point	4912 K (4639 °C)
Density	10.2 g/cm³

Energy properties

First ionization energy	7.092 eV
Electron affinity	0.746 eV

Atomic structure

Protons	42 (Atomic number)
Neutrons (Mo-98, most abundant isotope)	56
Electrons	42
Electron configuration	[Kr] 5s¹ 4d⁵
Oxidation states	+6
Electronegativity (Pauling)	2.16
Atomic radius (van der Waals)	209 pm

Ionization energies - NIST ASD (42 states)

State	Charge	Ioniz. energy (eV)	Type
Mo I	0+	7.09243 ± 0.00004	measured
Mo II	1+	16.16 ± 0.12	semi-empirical
Mo III	2+	27.13 ± 0.12	semi-empirical
Mo IV	3+	40.33 ± 0.06	semi-empirical
Mo V	4+	54.417 ± 0.019	semi-empirical
Mo VI	5+	68.82704 ± 0.00021	measured
Mo VII	6+	125.638 ± 0.025	semi-empirical
Mo VIII	7+	143.6 ± 1	measured
Mo IX	8+	164.12 ± 0.09	measured
Mo X	9+	186.3 ± 1.2	semi-empirical
Mo XI	10+	209.3 ± 1.2	calculated
Mo XII	11+	230.28 ± 0.06	semi-empirical
Mo XIII	12+	279.1 ± 0.5	semi-empirical
Mo XIV	13+	302.6 ± 0.04	measured
Mo XV	14+	544 ± 0.5	semi-empirical
Mo XVI	15+	591 ± 3	calculated
Mo XVII	16+	646 ± 3	calculated
Mo XVIII	17+	702 ± 3	calculated
Mo XIX	18+	758 ± 3	calculated
Mo XX	19+	829 ± 4	calculated
Mo XXI	20+	890 ± 4	calculated
Mo XXII	21+	953 ± 4	calculated
Mo XXIII	22+	1019 ± 4	calculated
Mo XXIV	23+	1082 ± 4	calculated
Mo XXV	24+	1263 ± 4	semi-empirical
Mo XXVI	25+	1319.6 ± 1.4	semi-empirical
Mo XXVII	26+	1385.1 ± 1.9	semi-empirical
Mo XXVIII	27+	1462 ± 6	semi-empirical
Mo XXIX	28+	1537 ± 3	semi-empirical
Mo XXX	29+	1587 ± 8	semi-empirical
Mo XXXI	30+	1730.1 ± 2.5	semi-empirical
Mo XXXII	31+	1790.93 ± 0.06	semi-empirical
Mo XXXIII	32+	4259 ± 2.4	semi-empirical
Mo XXXIV	33+	4430 ± 7	semi-empirical
Mo XXXV	34+	4618 ± 10	semi-empirical
Mo XXXVI	35+	4800 ± 30	semi-empirical
Mo XXXVII	36+	5084 ± 6	semi-empirical
Mo XXXVIII	37+	5287 ± 4	semi-empirical
Mo XXXIX	38+	5548 ± 5	semi-empirical
Mo XL	39+	5713.194 ± 0.016	calculated
Mo XLI	40+	23810.653 ± 0.009	calculated
Mo XLII	41+	24572.213 ± 0.004	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: Molybdenum (Mo) — © images-of-elements.com (CC BY 3.0)

Isotopes (39)

A	N	Half-life	Decay
Mo-81	39	unknown	EC/β⁺
Mo-82	40	unknown	EC/β⁺
Mo-83	41	10 ms	EC/β⁺
Mo-84	42	2.3 s	EC/β⁺
Mo-85	43	3.2 s	EC/β⁺
Mo-86	44	19.1 s	EC/β⁺
Mo-87	45	14.1 s	EC/β⁺
Mo-88	46	8.0 min	EC/β⁺
Mo-89	47	2.04 min	EC/β⁺
Mo-90	48	5.56 h	EC/β⁺
Mo-91	49	15.49 min	EC/β⁺
Mo-92	50	stable	-
Mo-93	51	4000 a	EC
Mo-94	52	stable	-
Mo-95	53	stable	-
Mo-96	54	stable	-
Mo-97	55	stable	-
Mo-98	56	stable	-
Mo-99	57	65.936 h	β⁻
Mo-100	58	7.07×10¹⁸ a	2β⁻
Mo-101	59	14.61 min	β⁻
Mo-102	60	11.3 min	β⁻
Mo-103	61	67.5 s	β⁻
Mo-104	62	59.4 s	β⁻
Mo-105	63	36.3 s	β⁻
Mo-106	64	8.73 s	β⁻
Mo-107	65	3.5 s	β⁻
Mo-108	66	1.106 s	β⁻
Mo-109	67	700 ms	β⁻
Mo-110	68	287 ms	β⁻
Mo-111	69	186 ms	β⁻
Mo-112	70	125 ms	β⁻
Mo-113	71	80 ms	β⁻
Mo-114	72	58 ms	β⁻
Mo-115	73	45.6 ms	β⁻
Mo-116	74	32 ms	β⁻
Mo-117	75	22 ms	β⁻
Mo-118	76	19 ms	β⁻
Mo-119	77	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