Element: Thorium

General data

Element name	Thorium
Chemical symbol	Th
Atomic number Z	90
Year discovered	1828
Standard state (25°C)	Solid
Category	Actinide
Block	f
Atomic mass	232.04
CPK color	#00BAFF

Physical properties

Melting point	2023 K (1750 °C)
Boiling point	5061 K (4788 °C)
Density	11.72 g/cm³

Energy properties

First ionization energy	6.08 eV
Electron affinity	no data

Atomic structure

Protons	90 (Atomic number)
Neutrons (Th-232, most abundant isotope)	142
Electrons	90
Electron configuration	[Rn] 7s² 6d²
Oxidation states	+4
Electronegativity (Pauling)	1.3
Atomic radius (van der Waals)	237 pm

Ionization energies - NIST ASD (90 states)

State	Charge	Ioniz. energy (eV)	Type
Th I	0+	6.3067 ± 0.00025	measured
Th II	1+	12.1 ± 0.2	measured
Th III	2+	18.32 ± 0.05	semi-empirical
Th IV	3+	28.648 ± 0.025	measured
Th V	4+	58 ± 1.9	calculated
Th VI	5+	69.1 ± 2	calculated
Th VII	6+	82 ± 2	calculated
Th VIII	7+	95 ± 2.1	calculated
Th IX	8+	118 ± 2.2	calculated
Th X	9+	133 ± 2.2	calculated
Th XI	10+	165 ± 2.4	calculated
Th XII	11+	181 ± 2.5	calculated
Th XIII	12+	262 ± 3	calculated
Th XIV	13+	285 ± 3	calculated
Th XV	14+	310 ± 3	calculated
Th XVI	15+	336 ± 3	calculated
Th XVII	16+	362 ± 3	calculated
Th XVIII	17+	389 ± 3	calculated
Th XIX	18+	424 ± 3	calculated
Th XX	19+	451 ± 4	calculated
Th XXI	20+	480 ± 4	calculated
Th XXII	21+	508 ± 4	calculated
Th XXIII	22+	650 ± 40	calculated
Th XXIV	23+	680 ± 30	calculated
Th XXV	24+	720 ± 40	calculated
Th XXVI	25+	750 ± 40	calculated
Th XXVII	26+	830 ± 40	calculated
Th XXVIII	27+	870 ± 40	calculated
Th XXIX	28+	970 ± 50	calculated
Th XXX	29+	1010 ± 50	calculated
Th XXXI	30+	1090 ± 50	calculated
Th XXXII	31+	1160 ± 60	calculated
Th XXXIII	32+	1240 ± 60	calculated
Th XXXIV	33+	1310 ± 60	calculated
Th XXXV	34+	1380 ± 70	calculated
Th XXXVI	35+	1460 ± 70	calculated
Th XXXVII	36+	1530 ± 80	calculated
Th XXXVIII	37+	1600 ± 80	calculated
Th XXXIX	38+	1680 ± 80	calculated
Th XL	39+	1760 ± 90	calculated
Th XLI	40+	1830 ± 90	calculated
Th XLII	41+	1910 ± 100	calculated
Th XLIII	42+	1980 ± 100	calculated
Th XLIV	43+	2060 ± 100	calculated
Th XLV	44+	2390 ± 4	calculated
Th XLVI	45+	2455 ± 4	calculated
Th XLVII	46+	2524 ± 4	calculated
Th XLVIII	47+	2598 ± 4	calculated
Th XLIX	48+	2669 ± 4	calculated
Th L	49+	2737 ± 4	calculated
Th LI	50+	2864 ± 4	calculated
Th LII	51+	2935 ± 4	calculated
Th LIII	52+	3013 ± 4	calculated
Th LIV	53+	3086 ± 5	calculated
Th LV	54+	3375 ± 5	calculated
Th LVI	55+	3445 ± 5	calculated
Th LVII	56+	3522 ± 5	calculated
Th LVIII	57+	3593 ± 6	calculated
Th LIX	58+	3943 ± 6	calculated
Th LX	59+	4025 ± 7	calculated
Th LXI	60+	4230 ± 10	calculated
Th LXII	61+	4313 ± 4	semi-empirical
Th LXIII	62+	6972 ± 15	calculated
Th LXIV	63+	7130 ± 19	calculated
Th LXV	64+	7299 ± 24	calculated
Th LXVI	65+	7480 ± 30	calculated
Th LXVII	66+	7650 ± 40	calculated
Th LXVIII	67+	7810 ± 40	calculated
Th LXIX	68+	8180 ± 50	calculated
Th LXX	69+	8350 ± 50	calculated
Th LXXI	70+	8550 ± 60	calculated
Th LXXII	71+	8720 ± 60	calculated
Th LXXIII	72+	9220 ± 70	calculated
Th LXXIV	73+	9370 ± 90	calculated
Th LXXV	74+	9540 ± 90	calculated
Th LXXVI	75+	9690 ± 100	calculated
Th LXXVII	76+	10790 ± 110	calculated
Th LXXVIII	77+	10970 ± 120	calculated
Th LXXIX	78+	11340 ± 120	calculated
Th LXXX	79+	11510 ± 140	calculated
Th LXXXI	80+	24060 ± 150	calculated
Th LXXXII	81+	24480 ± 160	calculated
Th LXXXIII	82+	24940 ± 170	calculated
Th LXXXIV	83+	25360 ± 190	calculated
Th LXXXV	84+	29410 ± 200	calculated
Th LXXXVI	85+	29970 ± 220	calculated
Th LXXXVII	86+	30680 ± 240	calculated
Th LXXXVIII	87+	31122.8 ± 0.6	calculated
Th LXXXIX	88+	123091 ± 0.6	calculated
Th XC	89+	125250.3 ± 0.7	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: Thorium (Th) — © images-of-elements.com (CC BY 3.0)

Isotopes (32)

A	N	Half-life	Decay
Th-207	117	10 ms	α
Th-208	118	3.1 ms	α
Th-209	119	2.5 ms	α
Th-210	120	16 ms	α
Th-211	121	40 ms	α
Th-212	122	31.7 ms	α
Th-213	123	146 ms	α
Th-214	124	100 ms	α
Th-215	125	1.4 s	α
Th-216	126	26.0 ms	α
Th-217	127	254 μs	α
Th-218	128	121 ns	α
Th-219	129	1.02 μs	α
Th-220	130	10.2 μs	α
Th-221	131	1.73 ms	α
Th-222	132	1.970 ms	α
Th-223	133	0.60 s	α
Th-224	134	1.04 s	α
Th-225	135	8.72 min	α
Th-226	136	30.69 min	α
Th-227	137	18.694 d	α
Th-228	138	1.9116 a	α
Th-229	139	7908 a	α
Th-230	140	75400 a	α
Th-231	141	25.52 h	β⁻
Th-232	142	1.407×10¹⁰ a	α
Th-233	143	21.83 min	β⁻
Th-234	144	24.107 d	β⁻
Th-235	145	7.2 min	β⁻
Th-236	146	37.5 min	β⁻
Th-237	147	4.8 min	β⁻
Th-238	148	9.4 min	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