Element: Einsteinium

General data

Element name	Einsteinium
Chemical symbol	Es
Atomic number Z	99
Year discovered	1952
Standard state (25°C)	Solid
Category	Actinide
Block	f
Atomic mass	[252]
CPK color	#B31FD4

Physical properties

Melting point	1133 K (860 °C)
Boiling point	no data
Density	no data

Energy properties

First ionization energy	6.42 eV
Electron affinity	no data

Atomic structure

Protons	99 (Atomic number)
Neutrons (Es-252, longest-lived isotope)	153
Electrons	99
Electron configuration	[Rn] 7s² 5f¹¹
Oxidation states	+3
Electronegativity (Pauling)	1.3
Atomic radius (van der Waals)	245 pm

Ionization energies - NIST ASD (99 states)

State	Charge	Ioniz. energy (eV)	Type
Es I	0+	6.3684 ± 0.00006	measured
Es II	1+	12.2 ± 0.4	semi-empirical
Es III	2+	22.7 ± 0.4	semi-empirical
Es IV	3+	38.8 ± 0.4	semi-empirical
Es V	4+	54.1 ± 1.9	calculated
Es VI	5+	71 ± 2	calculated
Es VII	6+	97 ± 2	calculated
Es VIII	7+	112.9 ± 2.1	calculated
Es IX	8+	137 ± 2.2	calculated
Es X	9+	157 ± 7	calculated
Es XI	10+	180 ± 9	calculated
Es XII	11+	206 ± 10	calculated
Es XIII	12+	231 ± 11	calculated
Es XIV	13+	252 ± 12	calculated
Es XV	14+	270 ± 14	calculated
Es XVI	15+	294 ± 15	calculated
Es XVII	16+	317 ± 16	calculated
Es XVIII	17+	342 ± 17	calculated
Es XIX	18+	367 ± 19	calculated
Es XX	19+	398 ± 4	calculated
Es XXI	20+	421 ± 4	calculated
Es XXII	21+	576 ± 4	calculated
Es XXIII	22+	606 ± 4	calculated
Es XXIV	23+	638 ± 4	calculated
Es XXV	24+	672 ± 4	calculated
Es XXVI	25+	705 ± 4	calculated
Es XXVII	26+	738 ± 4	calculated
Es XXVIII	27+	790 ± 4	calculated
Es XXIX	28+	824 ± 4	calculated
Es XXX	29+	861 ± 4	calculated
Es XXXI	30+	895 ± 4	calculated
Es XXXII	31+	1060 ± 50	calculated
Es XXXIII	32+	1100 ± 50	calculated
Es XXXIV	33+	1140 ± 60	calculated
Es XXXV	34+	1180 ± 60	calculated
Es XXXVI	35+	1310 ± 70	calculated
Es XXXVII	36+	1360 ± 70	calculated
Es XXXVIII	37+	1480 ± 70	calculated
Es XXXIX	38+	1530 ± 80	calculated
Es XL	39+	1690 ± 80	calculated
Es XLI	40+	1780 ± 90	calculated
Es XLII	41+	1870 ± 90	calculated
Es XLIII	42+	1950 ± 100	calculated
Es XLIV	43+	2040 ± 100	calculated
Es XLV	44+	2130 ± 110	calculated
Es XLVI	45+	2220 ± 110	calculated
Es XLVII	46+	2300 ± 120	calculated
Es XLVIII	47+	2410 ± 120	calculated
Es XLIX	48+	2490 ± 120	calculated
Es L	49+	2580 ± 120	calculated
Es LI	50+	2680 ± 140	calculated
Es LII	51+	2760 ± 140	calculated
Es LIII	52+	2850 ± 140	calculated
Es LIV	53+	3294 ± 5	calculated
Es LV	54+	3370 ± 5	calculated
Es LVI	55+	3449 ± 5	calculated
Es LVII	56+	3535 ± 5	calculated
Es LVIII	57+	3616 ± 6	calculated
Es LIX	58+	3694 ± 6	calculated
Es LX	59+	3866 ± 7	calculated
Es LXI	60+	3947 ± 10	calculated
Es LXII	61+	4038 ± 12	calculated
Es LXIII	62+	4120 ± 15	calculated
Es LXIV	63+	4456 ± 19	calculated
Es LXV	64+	4537 ± 24	calculated
Es LXVI	65+	4620 ± 30	calculated
Es LXVII	66+	4700 ± 40	calculated
Es LXVIII	67+	5260 ± 40	calculated
Es LXIX	68+	5350 ± 50	calculated
Es LXX	69+	5600 ± 50	calculated
Es LXXI	70+	5690 ± 60	calculated
Es LXXII	71+	8960 ± 60	calculated
Es LXXIII	72+	9140 ± 70	calculated
Es LXXIV	73+	9330 ± 90	calculated
Es LXXV	74+	9530 ± 90	calculated
Es LXXVI	75+	9720 ± 100	calculated
Es LXXVII	76+	9910 ± 110	calculated
Es LXXVIII	77+	10400 ± 120	calculated
Es LXXIX	78+	10590 ± 120	calculated
Es LXXX	79+	10810 ± 140	calculated
Es LXXXI	80+	11010 ± 150	calculated
Es LXXXII	81+	11570 ± 160	calculated
Es LXXXIII	82+	11740 ± 170	calculated
Es LXXXIV	83+	11930 ± 190	calculated
Es LXXXV	84+	12110 ± 200	calculated
Es LXXXVI	85+	13810 ± 220	calculated
Es LXXXVII	86+	14030 ± 240	calculated
Es LXXXVIII	87+	14460 ± 250	calculated
Es LXXXIX	88+	14700 ± 300	calculated
Es XC	89+	29700 ± 300	calculated
Es XCI	90+	30100 ± 300	calculated
Es XCII	91+	30700 ± 300	calculated
Es XCIII	92+	31100 ± 400	calculated
Es XCIV	93+	37400 ± 400	calculated
Es XCV	94+	38100 ± 400	calculated
Es XCVI	95+	38900 ± 400	calculated
Es XCVII	96+	39451.4 ± 1	calculated
Es XCVIII	97+	154344 ± 6	calculated
Es XCIX	98+	156927 ± 6	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: Einsteinium (Es) — © images-of-elements.com (CC BY 3.0)

Isotopes (18)

A	N	Half-life	Decay
Es-240	141	6.7 s	α
Es-241	142	4.3 s	α
Es-242	143	17.8 s	α
Es-243	144	22 s	α
Es-244	145	37 s	EC/β⁺
Es-245	146	1.12 min	α
Es-246	147	7.5 min	EC/β⁺
Es-247	148	4.6 min	EC/β⁺
Es-248	149	24 min	EC/β⁺
Es-249	150	102.2 min	EC/β⁺
Es-250	151	8.5 h	EC/β⁺
Es-251	152	33 h	EC
Es-252	153	471.7 d	α
Es-253	154	20.466 d	α
Es-254	155	275.7 d	α
Es-255	156	39.8 d	β⁻
Es-256	157	25.4 min	β⁻
Es-257	158	7.7 d	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