H 1

Hydrogen (H)

nonmetal

Period: 1 Group: 1 Block: s

Gas

Standard Atomic Weight

Electron configuration

1s¹

Melting point

-259.34 °C (13.81 K)

Boiling point

-252.87 °C (20.28 K)

Density

0.08988 kg/m³

Oxidation states

−1, +1

Electronegativity (Pauling)

2.2

Ionization energy (1st)

Discovery year

1766

Atomic radius

25 pm

Details

Name origin Greek: hydro (water) and genes (generate)

Discovery country England

Discoverers Henry Cavendish

The lightest chemical element, hydrogen sits above the alkali metals but is a nonmetal under ordinary conditions. Its single proton and one electron make it the simplest atom and a reference point for much of chemistry. On Earth it is usually bound in water and organic matter, while industry uses it as a chemical feedstock, reducing agent, fuel, and energy carrier.

Colourless, odourless gaseous chemical element. Lightest and most abundant element in the universe. Present in water and in all organic compounds. Chemically reacts with most elements. Discovered by Henry Cavendish in 1776.

The name derives from the Greek hydro for "water" and genes for "forming" because it burned in air to form water. Hydrogen was discovered by the English physicist Henry Cavendish in 1766.

Scientists had been producing hydrogen for years before it was recognized as an element. Written records indicate that Robert Boyle produced hydrogen gas as early as 1671 while experimenting with iron and acids. Hydrogen was first recognized as a distinct element by Henry Cavendish in 1766. Composed of a single proton and a single electron, hydrogen is the simplest and most abundant element in the universe. It is estimated that 90% of the visible universe is composed of hydrogen.

Hydrogen is the raw fuel that most stars 'burn' to produce energy. The same process, known as fusion, is being studied as a possible power source for use on earth. The sun's supply of hydrogen is expected to last another 5 billion years.

From the Greek word hydro (water), and genes (forming). Hydrogen was recognized as a distinct substance by Henry Cavendish in 1776. Diagram of a simple hydrogen atom.

Hydrogen is the most abundant of all elements in the universe. The heavier elements were originally made from hydrogen atoms or from other elements that were originally made from hydrogen atoms.

Read about Hydrogen on Wikipedia

Images

Properties

Physical

Atomic radius (empirical) 25 pm

Covalent radius 31 pm

Van der Waals radius 120 pm

Density

Molar volume 0.0141 L/mol

Phase at STP gas

Melting point -259.34 °C

Boiling point -252.87 °C

Thermal conductivity 0.181 W/(m·K)

Specific heat capacity 14.304 J/(g·K)

Molar heat capacity 28.836 J/(mol·K)

Crystal structure hcp

Chemical

Electronegativity (Pauling) 2.2

Electronegativity (Allen) 2.3

Electron affinity

Ionization energy (1st)

Oxidation states −1, +1

Valence electrons 1

Electron configuration

Electron configuration (semantic)

Thermodynamic

Triple point (temperature) -259.3467 °C

Triple point (pressure) 7041 Pa

Critical point (temperature) -240.212 °C

Critical point (pressure) 1.285800e+6 Pa

Heat of fusion 0.00121262 eV

Heat of vaporization 0.00936933 eV

Heat of atomization 2.259398 eV

Atomization enthalpy

Nuclear

Stable isotopes 2

Discovery year 1766

Abundance

Abundance (Earth's crust) 1400 mg/kg

Abundance (ocean)

Reactivity

N/A

Crystal Structure

Lattice constant a 375 pm

Electronic Structure

Electrons per shell 1

Identifiers

CAS number 1333-74-0

Term symbol

InChI InChI=1S/H

InChI Key YZCKVEUIGOORGS-UHFFFAOYSA-N

Electron Configuration Measured

Ion charge

Protons 1

Electrons 1

Charge Neutral

Configuration H: 1s¹

1s¹

Orbital diagram

↑

1/2 1↑

Total electrons: 1 Unpaired: 1

Atomic model

Protons 1

Neutrons 0

Electrons 1

Mass number 1

Stability Stable

Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.

Schematic atomic model, not to scale.

Atomic Fingerprint

Emission / Absorption Spectrum

Emission Visible: 380–750 nm

Isotope Distribution

Mass number	Atomic mass (u)	Natural abundance	Half-life
1 Stable	1.00782503223 ± 0.00000000009	99.9885%	Stable
2 Stable	2.01410177812 ± 0.00000000012	0.0115%	Stable

Measured

Phase / State

Gas 25 °C (298.15 K)

Reason: 277.9 °C above boiling point (-252.87 °C)

Melting point -259.34 °C

Boiling point -252.87 °C

Above boiling by 277.9 °C

0 K Current temperature: 25 °C 6000 K

Phase timeline

Schematic, not to scale

Solid

Liquid

Gas

Melting

Boiling

25°C

Solid

Liquid

Gas

Current

Phase transition points

Melting point Literature

-259.34 °C

Boiling point Literature

-252.87 °C

Current phase Calculated
Gas

Transition energies

Heat of fusion Literature

0.00121262 eV

Energy required to melt 1 mol at melting point

Heat of vaporization Literature

0.00936933 eV

Energy required to vaporize 1 mol at boiling point

Density

Reference density Literature

0.08988 kg/m³

At standard conditions

Current density Estimated

0.04120002 kg/m³

Estimated via ideal gas law at current T

Advanced

Triple point Literature

-259.3467 °C

Critical point Literature

-240.212 °C

Atomic Spectra

Lines Holdings ?

Ion	Total lines	Transition probabilities	Level designations
D I Isotope	364	161	341
H I	568	441	535
T I Isotope	11	11	11

NIST Lines Holdings →

Levels Holdings ?

Ion	Charge	Levels
D I Isotope	0	78
H I	0	106
T I Isotope	0	10

NIST Levels Holdings →

1 H 1.007975

Hydrogen — Atomic Orbital Visualizer

1s1

Energy levels 1

Oxidation states -1, +1

HOMO 1s n=1 · l=0 · m=0

Hydrogen — Atomic Orbital Visualizer Preview

Three.js loads only on request

1 H 1.007975

Hydrogen — Crystal Structure Visualizer

Primitive Hexagonal · Pearson hP2

Experimental

Pearson hP2

Coord. № 12

Packing 74.048%

No crystal structure at standard conditions — gas at 298 K, 1 atm

Solid phase structure at 293 K

Hydrogen — Crystal Structure Visualizer Preview

Three.js loads only on request

Compounds

H+

1.008 u

H-

1.008 u

H+

1.008 u

H+

2.014 u

H+

3.016 u

2.014 u

H-

3.016 u

H-

2.014 u

H-

1.008 u

Isotopes (2)

The ordinary isotope of hydrogen, H, is known as Protium, the other two isotopes are Deuterium (a proton and a neutron) and Tritium (a protron and two neutrons). Hydrogen is the only element whose isotopes have been given different names. Deuterium and Tritium are both used as fuel in nuclear fusion reactors. One atom of Deuterium is found in about 6000 ordinary hydrogen atoms.

	Mass number	Atomic mass (u)	Natural abundance	Half-life	Decay mode
	1 Stable	1.00782503223 ± 0.00000000009	99.9885% ± 0.0070%	Stable	stable
	2 Stable	2.01410177812 ± 0.00000000012	0.0115% ± 0.0070%	Stable	stable

1 Stable

Atomic mass (u) 1.00782503223 ± 0.00000000009

Natural abundance 99.9885% ± 0.0070%

Half-life Stable

Decay mode

stable

2 Stable

Atomic mass (u) 2.01410177812 ± 0.00000000012

Natural abundance 0.0115% ± 0.0070%

Half-life Stable

Decay mode

stable

Spectral Lines

Wavelength (nm)	Intensity	Ion stage	Type	Transition	Accuracy	Source
383.5355892 nm	N/A	H I	emission	2p 2P* → 9d 2D	Measured	NIST
383.5356424 nm	N/A	H I	emission	2p 2P* → 9s 2S	Measured	NIST
383.53587 nm	N/A	H I	emission	N/A	Measured	NIST
383.5361082 nm	N/A	H I	emission	2s 2S → 9p 2P*	Measured	NIST
383.5361616 nm	N/A	H I	emission	2s 2S → 9s 2S	Measured	NIST
383.5361673 nm	N/A	H I	emission	2s 2S → 9p 2P*	Measured	NIST
383.53839 nm	N/A	H I	emission	N/A	Measured	NIST
383.53909 nm	30000	H I	emission	2 → 9	Measured	NIST
383.5409535 nm	N/A	H I	emission	2p 2P* → 9d 2D	Measured	NIST
383.54096 nm	N/A	H I	emission	N/A	Measured	NIST
383.5409732 nm	N/A	H I	emission	2p 2P* → 9d 2D	Measured	NIST
383.5410263 nm	N/A	H I	emission	2p 2P* → 9s 2S	Measured	NIST
388.9019815 nm	N/A	H I	emission	2p 2P* → 8d 2D	Measured	NIST
388.9020595 nm	N/A	H I	emission	2p 2P* → 8s 2S	Measured	NIST
388.90227 nm	N/A	H I	emission	N/A	Measured	NIST
388.9024865 nm	N/A	H I	emission	2s 2S → 8d 2D	Measured	NIST
388.9025152 nm	N/A	H I	emission	2s 2S → 8p 2P*	Measured	NIST
388.9025154 nm	N/A	H I	emission	2s 2S → 8d 2D	Measured	NIST
388.9025933 nm	N/A	H I	emission	2s 2S → 8s 2S	Measured	NIST
388.9026017 nm	N/A	H I	emission	2s 2S → 8p 2P*	Measured	NIST
388.90486 nm	N/A	H I	emission	N/A	Measured	NIST
388.90557 nm	70000	H I	emission	2 → 8	Measured	NIST
388.9074883 nm	N/A	H I	emission	2p 2P* → 8d 2D	Measured	NIST
388.90749 nm	N/A	H I	emission	N/A	Measured	NIST
388.9075172 nm	N/A	H I	emission	2p 2P* → 8d 2D	Measured	NIST
388.9075951 nm	N/A	H I	emission	2p 2P* → 8s 2S	Measured	NIST
397.0041763 nm	N/A	H I	emission	2p 2P* → 7d 2D	Measured	NIST
397.0042976 nm	N/A	H I	emission	2p 2P* → 7s 2S	Measured	NIST
397.00448 nm	N/A	H I	emission	N/A	Measured	NIST
397.0047325 nm	N/A	H I	emission	2s 2S → 7p 2P*	Measured	NIST
397.0048539 nm	N/A	H I	emission	2s 2S → 7s 2S	Measured	NIST
397.004867 nm	N/A	H I	emission	2s 2S → 7p 2P*	Measured	NIST
397.00719 nm	N/A	H I	emission	N/A	Measured	NIST
397.00788 nm	30000	H I	emission	2 → 7	Measured	NIST
397.0099002 nm	N/A	H I	emission	2p 2P* → 7d 2D	Measured	NIST
397.00991 nm	N/A	H I	emission	N/A	Measured	NIST
397.009945 nm	N/A	H I	emission	2p 2P* → 7d 2D	Measured	NIST
397.0100663 nm	N/A	H I	emission	2p 2P* → 7s 2S	Measured	NIST
410.1702284 nm	N/A	H I	emission	2p 2P* → 6d 2D	Measured	NIST
410.1704339 nm	N/A	H I	emission	2p 2P* → 6s 2S	Measured	NIST
410.17056 nm	N/A	H I	emission	N/A	Measured	NIST
410.1707462 nm	N/A	H I	emission	2s 2S → 6d 2D	Measured	NIST
410.1708218 nm	N/A	H I	emission	2s 2S → 6p 2P*	Measured	NIST
410.1710277 nm	N/A	H I	emission	2s 2S → 6s 2S	Measured	NIST
410.1710499 nm	N/A	H I	emission	2s 2S → 6p 2P*	Measured	NIST
410.17346 nm	N/A	H I	emission	N/A	Measured	NIST
410.17415 nm	70000	H I	emission	2 → 6	Measured	NIST
410.17631 nm	N/A	H I	emission	2p 2P* → 6d 2D	Measured	NIST
410.17632 nm	N/A	H I	emission	N/A	Measured	NIST
410.176386 nm	N/A	H I	emission	2p 2P* → 6d 2D	Measured	NIST
410.1765915 nm	N/A	H I	emission	2p 2P* → 6s 2S	Measured	NIST
434.0426937 nm	N/A	H I	emission	2p 2P* → 5d 2D	Measured	NIST
434.04309 nm	N/A	H I	emission	N/A	Measured	NIST
434.0430904 nm	N/A	H I	emission	2p 2P* → 5s 2S	Measured	NIST
434.0433568 nm	N/A	H I	emission	2s 2S → 5p 2P*	Measured	NIST
434.0437554 nm	N/A	H I	emission	2s 2S → 5s 2S	Measured	NIST
434.0437982 nm	N/A	H I	emission	2s 2S → 5p 2P*	Measured	NIST
434.04634 nm	N/A	H I	emission	N/A	Measured	NIST
434.0471 nm	90000	H I	emission	2 → 5	Measured	NIST
434.0494419 nm	N/A	H I	emission	2p 2P* → 5d 2D	Measured	NIST
434.04947 nm	N/A	H I	emission	N/A	Measured	NIST
434.0495889 nm	N/A	H I	emission	2p 2P* → 5d 2D	Measured	NIST
434.0499857 nm	N/A	H I	emission	2p 2P* → 5s 2S	Measured	NIST
486.1278624 nm	N/A	H I	emission	2p 2P* → 4d 2D	Measured	NIST
486.1283363 nm	N/A	H I	emission	2s 2S → 4d 2D	Measured	NIST
486.12841 nm	N/A	H I	emission	N/A	Measured	NIST
486.1286949 nm	N/A	H I	emission	2s 2S → 4p 2P*	Measured	NIST
486.128837 nm	N/A	H I	emission	2p 2P* → 4s 2S	Measured	NIST
486.1296711 nm	N/A	H I	emission	2s 2S → 4s 2S	Measured	NIST
486.1297761 nm	N/A	H I	emission	2s 2S → 4p 2P*	Measured	NIST
486.1325 nm	N/A	H I	emission	N/A	Measured	NIST
486.1333 nm	180000	H I	emission	2 → 4	Measured	NIST
486.1361516 nm	N/A	H I	emission	2p 2P* → 4d 2D	Measured	NIST
486.13622 nm	N/A	H I	emission	N/A	Measured	NIST
486.1365118 nm	N/A	H I	emission	2p 2P* → 4d 2D	Measured	NIST
486.1374864 nm	N/A	H I	emission	2p 2P* → 4s 2S	Measured	NIST
656.27097 nm	N/A	H I	emission	2p 2P* → 3d 2D	Measured	NIST
656.2714 nm	N/A	H I	emission	N/A	Measured	NIST
656.2722 nm	N/A	H I	emission	N/A	Measured	NIST
656.272483 nm	N/A	H I	emission	2s 2S → 3p 2P*	Measured	NIST
656.275181 nm	N/A	H I	emission	2p 2P* → 3s 2S	Measured	NIST
656.276701 nm	N/A	H I	emission	2s 2S → 3s 2S	Measured	NIST
656.277 nm	N/A	H I	emission	N/A	Measured	NIST
656.277153 nm	N/A	H I	emission	2s 2S → 3p 2P*	Measured	NIST
656.2795 nm	N/A	H I	emission	N/A	Measured	NIST
656.2819 nm	500000	H I	emission	2 → 3	Measured	NIST
656.285177 nm	N/A	H I	emission	2p 2P* → 3d 2D	Measured	NIST
656.28533 nm	N/A	H I	emission	N/A	Measured	NIST
656.2854 nm	N/A	H I	emission	N/A	Measured	NIST
656.286734 nm	N/A	H I	emission	2p 2P* → 3d 2D	Measured	NIST
656.290944 nm	N/A	H I	emission	2p 2P* → 3s 2S	Measured	NIST

Extended Properties

Covalent Radii (Extended)

Covalent radius (Pyykkö)

Van der Waals Radii

Bondi

Alvarez

UFF

MM3

Dreiding

Rowland–Taylor

Atomic & Metallic Radii

Atomic radius (Rahm)

Metallic radius (C12)

Numbering Scales

Mendeleev

Pettifor

Glawe

Electronegativity Scales

Ghosh

Miedema

Gunnarsson–Lundqvist

Robles–Bartolotti

Polarizability & Dispersion

Dipole polarizability

Dipole polarizability (unc.)

C₆

C₆ (Gould–Bučko)

Miedema Parameters

Miedema molar volume

Miedema electron density

Phase Transitions & Allotropes

Melting point	13.99 K
Boiling point	20.27 K
Critical point (temperature)	32.94 K
Critical point (pressure)	1.29 MPa
Triple point (temperature)	13.8 K
Triple point (pressure)	7.04 kPa

Oxidation State Categories

+1 main

−1 main

Advanced Reference Data

Screening Constants (1)

n	Orbital	σ
1	s	0

Crystal Radii Detail (2)

Charge	CN	Spin	r_crystal (pm)	Origin
1	I		-24
1	II		-4

Isotope Decay Modes (6)

Isotope	Mode	Intensity
3	B-	100%
4	n	100%
5	2n	100%
6	n	—
6	3n	—
7	2n	—

X‑ray Scattering Factors (501)

Energy (eV)	f₁	f₂
10	—	0
10.1617	—	0
10.3261	—	0
10.4931	—	0
10.6628	—	0
10.8353	—	0
11.0106	—	0
11.1886	—	0
11.3696	—	0
11.5535	—	0

Additional Data

Estimated Crustal Abundance

The estimated element abundance in the earth's crust.

1.40×103 milligrams per kilogram

References (1)

[5] Hydrogen https://education.jlab.org/itselemental/ele001.html

Estimated Oceanic Abundance

The estimated element abundance in the earth's oceans.

1.08×105 milligrams per liter

References (1)

[5] Hydrogen https://education.jlab.org/itselemental/ele001.html

Sources

Sources of this element.

Hydrogen is estimated to make up more than 90% of all the atoms three quarters of the mass of the universe! This element is found in the stars, and plays an important part in powering the universe through both the proton-proton reaction and carbon-nitrogen cycle. Stellar hydrogen fusion processes release massive amounts of energy by combining hydrogens to form helium.

Production of hydrogen in the U.S. alone amounts to about 3 billion cubic feet per year. Hydrogen is prepared by

▸ steam on heated carbon,

▸ decomposition of certain hydrocarbons with heat,

▸ reaction of sodium or potassium hydroxide on aluminum

▸ electrolysis of water, or

▸ displacement from acids by certain metals.

Liquid hydrogen is important in cryogenics and in the study of superconductivity, as its melting point is only 20 degrees above absolute zero.

Tritium is readily produced in nuclear reactors and is used in the production of the hydrogen bomb.

Hydrogen is the primary component of Jupiter and the other gas giant planets. At some depth in the planet's interior the pressure is so great that solid molecular hydrogen is converted to solid metallic hydrogen.

In 1973, a group of Russian experimenters may have produced metallic hydrogen at a pressure of 2.8 Mbar. At the transition the density changed from 1.08 to 1.3 g/cm3. Earlier, in 1972, at Livermore, California, a group also reported on a similar experiment in which they observed a pressure-volume point centered at 2 Mbar. Predictions say that metallic hydrogen may be metastable; others have predicted it would be a superconductor at room temperature.

References (1)

[6] Hydrogen https://periodic.lanl.gov/1.shtml

Isotopes in Forensic Science and Anthropology

Information on the use of this element's isotopes in forensic science and anthropology.

Measurements of relative 2H abundances are used to determine the breeding grounds of many species of migrant songbirds. These species of songbirds only grow their feathers before migration, and they grow them on or close to their breeding grounds. Therefore, the isotopic composition of a bird’s feathers correlates to the isotopic composition of the growing season’s precipitation [18] [18] Z. D. Sharp, V. Atudorei, H. O. Panarello, J. Fernández, C. Douthitt. J. Archaeolog. Sci.30, 1709 (2003).[18] Z. D. Sharp, V. Atudorei, H. O. Panarello, J. Fernández, C. Douthitt. J. Archaeolog. Sci.30, 1709 (2003)., [19] [19] K. A. Hobson. Oecologia120, 314 (1999).[19] K. A. Hobson. Oecologia120, 314 (1999)., [20] [20] K. A. Hobson, L. I. Wassenaar. Oecologia.109, 142 (1996).[20] K. A. Hobson, L. I. Wassenaar. Oecologia.109, 142 (1996)..

Measurements of relative 2H abundances of human hair samples collected at archeological sites are used to determine the geographic region in which a subject lived based on the hydrogen isotopic composition of the water they drank. This is possible because hair stores a daily record of the hydrogen isotopic composition of intake water, which correlates to local meteoric water [18] [18] Z. D. Sharp, V. Atudorei, H. O. Panarello, J. Fernández, C. Douthitt. J. Archaeolog. Sci.30, 1709 (2003).[18] Z. D. Sharp, V. Atudorei, H. O. Panarello, J. Fernández, C. Douthitt. J. Archaeolog. Sci.30, 1709 (2003)., [21] [21] T. B. Coplen, H. Qi. Forensic Sci. Int.266, 222 (2016).[21] T. B. Coplen, H. Qi. Forensic Sci. Int.266, 222 (2016)..

References (5)

[18] Z. D. Sharp, V. Atudorei, H. O. Panarello, J. Fernández, C. Douthitt. J. Archaeolog. Sci.30, 1709 (2003).
[19] K. A. Hobson. Oecologia120, 314 (1999).
[20] K. A. Hobson, L. I. Wassenaar. Oecologia.109, 142 (1996).
[21] T. B. Coplen, H. Qi. Forensic Sci. Int.266, 222 (2016).
[4] IUPAC Periodic Table of the Elements and Isotopes (IPTEI) https://doi.org/10.1515/pac-2015-0703

References

(9)

1 PubChem

Data deposited in or computed by PubChem

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2 Atomic Mass Data Center (AMDC), International Atomic Energy Agency (IAEA)

The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.

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3 IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW)

Hydrogen

Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.

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4 IUPAC Periodic Table of the Elements and Isotopes (IPTEI)

The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.

Visit source License

License note: Copyright (c) 2020 International Union of Pure and Applied Chemistry. The International Union of Pure and Applied Chemistry (IUPAC) contribution within Pubchem is provided under a CC-BY-NC-ND 4.0 license, unless otherwise stated.

5 Jefferson Lab, U.S. Department of Energy

Hydrogen

Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/

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License note: Please see citation and linking information: https://education.jlab.org/faq/index.html

6 Los Alamos National Laboratory, U.S. Department of Energy

Hydrogen

The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.

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7 NIST Physical Measurement Laboratory

Hydrogen

The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database

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8 PubChem Elements

Hydrogen

This section provides all form of data related to element Hydrogen.

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9 PubChem Elements

Hydrogen

The element property data was retrieved from publications.

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Last updated: May 1, 2026

Data verified: May 12, 2026

Content is reviewed against latest scientific data.