Ca 20

Calcium (Ca)

alkaline-earth-metal

Period: 4 Group: 2 Block: s

Solid

Standard Atomic Weight

Electron configuration

[Ar] 4s²

Melting point

841.85 °C (1115 K)

Boiling point

1483.85 °C (1757 K)

Density

1540 kg/m³

Oxidation states

+1, +2

Electronegativity (Pauling)

Ionization energy (1st)

Discovery year

1808

Atomic radius

180 pm

Details

Name origin Latin: calx, calcis (lime).

Discovery country England

Discoverers Sir Humphrey Davy

Calcium is an alkaline earth metal and the fifth most abundant element in Earth’s crust by mass. It is highly reactive as a free metal but widespread in stable minerals, especially carbonates, sulfates, phosphates, and silicates. Calcium chemistry is dominated by the Ca²⁺ ion, which is hard, strongly hydrated, and central to limestone formation, cement chemistry, seawater buffering, bones, teeth, shells, and many cellular signaling processes.

The metal has a silvery color, is rather hard, and is prepared by electrolysis of fused chloride and calcium fluoride (to lower the melting point).

Chemically it is one of the alkaline earth elements; it readily forms a white coating of nitride in air, reacts with water, burns with a yellow-red flame.

The name derives from the Latin calx for "lime" (CaO) or "limestone" (CaCO3) in which it was found. It was first isolated by British chemist Humphry Davy in 1808 with help from the Swedish chemist Jöns Jacob Berzelius and the Swedish court physician M. M. af Pontin.

Although calcium is the fifth most abundant element in the earth's crust, it is never found free in nature since it easily forms compounds by reacting with oxygen and water. Metallic calcium was first isolated by Sir Humphry Davy in 1808 through the electrolysis of a mixture of lime (CaO) and mercuric oxide (HgO). Today, metallic calcium is obtained by displacing calcium atoms in lime with atoms of aluminum in hot, low-pressure containers. About 4.2% of the earth's crust is composed of calcium.

From the Latin word calx, lime. Though lime was prepared by the Romans in the first century under the name calx, the metal was not discovered until 1808. After learning that Berzelius and Pontin prepared calcium amalgam by electrolyzing lime in mercury, Davy was able to isolate the impure metal.

Read about Calcium on Wikipedia

Images

Properties

Physical

Atomic radius (empirical) 180 pm

Covalent radius 176 pm

Van der Waals radius 231 pm

Metallic radius 174 pm

Density

Molar volume 0.0299 L/mol

Phase at STP solid

Melting point 841.85 °C

Boiling point 1483.85 °C

Specific heat capacity 0.647 J/(g·K)

Molar heat capacity 25.929 J/(mol·K)

Crystal structure fcc

Chemical

Electronegativity (Pauling) 1

Electronegativity (Allen) 1.034

Electron affinity

Ionization energy (1st)

Ionization energy (2nd)

Ionization energy (3rd)

Ionization energy (4th)

Ionization energy (5th)

Oxidation states +1, +2

Valence electrons 2

Electron configuration

Electron configuration (semantic)

Thermodynamic

Heat of fusion 0.08851117 eV

Heat of vaporization 1.603358 eV

Heat of sublimation 1.846919 eV

Heat of atomization 1.846919 eV

Atomization enthalpy

Nuclear

Stable isotopes 3

Discovery year 1808

Abundance

Abundance (Earth's crust) 4.150e+4 mg/kg

Abundance (ocean)

Reactivity

N/A

Crystal Structure

Lattice constant a 558 pm

Electronic Structure

Electrons per shell 2, 8, 8, 2

Identifiers

CAS number 7440-70-2

Term symbol

InChI InChI=1S/Ca

InChI Key OYPRJOBELJOOCE-UHFFFAOYSA-N

Electron Configuration Measured

Ion charge

Protons 20

Electrons 20

Charge Neutral

Configuration Ca: 4s²

[Ar] 4s²

1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

Orbital diagram

↑↓

2/2

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

6/6

↑↓

2/2

Total electrons: 20 Unpaired: 0

Atomic model

Protons 20

Neutrons 24

Electrons 20

Mass number 44

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
42 Stable	41.95861783 ± 0.00000016	0.6470%	Stable
43 Stable	42.95876644 ± 0.00000024	0.1350%	Stable
44 Stable	43.95548156 ± 0.00000035	2.0860%	Stable
46 Stable	45.953689 ± 0.0000024	0.0040%	Stable

Measured

Phase / State

Solid 25 °C (298.15 K)

Reason: 816.9 °C below melting point (841.85 °C)

Melting point 841.85 °C

Boiling point 1483.85 °C

Below melting by 816.9 °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

841.85 °C

Boiling point Literature

1483.85 °C

Current phase Calculated
Solid

Transition energies

Heat of fusion Literature

0.08851117 eV

Energy required to melt 1 mol at melting point

Heat of vaporization Literature

1.603358 eV

Energy required to vaporize 1 mol at boiling point

Heat of sublimation Literature

1.846919 eV

Energy required to sublime 1 mol at sublimation point

Density

Reference density Literature

1540 kg/m³

At standard conditions

Current density Calculated

1540 kg/m³

At standard conditions

Atomic Spectra

Showing 10 of 20 Atomic Spectra. Sorted by ion charge (ascending).

Lines Holdings ?

Ion	Charge	Total lines	Transition probabilities	Level designations
Ca I	0	206	136	137
Ca II	+1	149	99	99
Ca III	+2	676	530	676
Ca IV	+3	40	3	3
Ca V	+4	53	18	18
Ca VI	+5	20	18	20
Ca VII	+6	18	18	18
Ca VIII	+7	6	6	6
Ca IX	+8	26	26	26
Ca X	+9	25	25	25

NIST Lines Holdings →

Levels Holdings ?

Ion	Charge	Levels
Ca I	0	787
Ca II	+1	72
Ca III	+2	182
Ca IV	+3	71
Ca V	+4	40
Ca VI	+5	32
Ca VII	+6	27
Ca VIII	+7	38
Ca IX	+8	72
Ca X	+9	52

NIST Levels Holdings →

20 Ca 40.078

Calcium — Atomic Orbital Visualizer

[Ar]4s2

Energy levels 2 8 8 2

Oxidation states +1, +2

HOMO 4s n=4 · l=0 · m=0

Calcium — Atomic Orbital Visualizer Preview

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20 Ca 40.078

Calcium — Crystal Structure Visualizer

Face-Centered Cubic · Pearson cF4

Experimental

Pearson cF4

Coord. № 12

Packing 74.000%

Calcium — Crystal Structure Visualizer Preview

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Ionic Radii

Charge	Coordination	Spin	Radius
+2	6	N/A	100 pm
+2	7	N/A	106 pm
+2	8	N/A	112.00000000000001 pm
+2	9	N/A	118 pm
+2	10	N/A	123 pm
+2	12	N/A	134 pm

Compounds

Ca+2

40.080 u

39.963 u

44.956 u

46.955 u

40.962 u

41.959 u

42.959 u

47.953 u

43.955 u

Ca+2

44.956 u

45.954 u

48.956 u

Ca+2

46.955 u

Ca+2

42.959 u

Isotopes (4)

Mass number	Atomic mass (u)	Natural abundance	Half-life	Decay mode
42 Stable	41.95861783 ± 0.00000016	0.6470% ± 0.0230%	Stable	stable
43 Stable	42.95876644 ± 0.00000024	0.1350% ± 0.0100%	Stable	stable
44 Stable	43.95548156 ± 0.00000035	2.0860% ± 0.1100%	Stable	stable
46 Stable	45.953689 ± 0.0000024	0.0040% ± 0.0030%	Stable	stable

42 Stable

Atomic mass (u) 41.95861783 ± 0.00000016

Natural abundance 0.6470% ± 0.0230%

Half-life Stable

Decay mode

stable

43 Stable

Atomic mass (u) 42.95876644 ± 0.00000024

Natural abundance 0.1350% ± 0.0100%

Half-life Stable

Decay mode

stable

44 Stable

Atomic mass (u) 43.95548156 ± 0.00000035

Natural abundance 2.0860% ± 0.1100%

Half-life Stable

Decay mode

stable

46 Stable

Atomic mass (u) 45.953689 ± 0.0000024

Natural abundance 0.0040% ± 0.0030%

Half-life Stable

Decay mode

stable

Spectral Lines

Showing 50 of 247 Spectral Lines. Only spectral lines with measured intensity are shown by default.

Wavelength (nm)	Intensity	Ion stage	Type	Transition	Accuracy	Source
408.1762 nm	1000	Ca III	emission	3s2.3p5.4s 1P* → 3s2.3p5.4p 3S	Measured	NIST
449.9885 nm	1000	Ca III	emission	3s2.3p5.(2P<1/2>).4d 2[5/2] → 3s2.3p5.(2P*<1/2>).4f 2[7/2]	Measured	NIST
420.7216 nm	800	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[3/2] → 3s2.3p5.(2P*<3/2>).4f 2[5/2]	Measured	NIST
430.2803 nm	800	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[7/2] → 3s2.3p5.(2P*<3/2>).4f 2[9/2]	Measured	NIST
439.9584 nm	800	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[7/2] → 3s2.3p5.(2P*<3/2>).4f 2[9/2]	Measured	NIST
423.3736 nm	700	Ca III	emission	3s2.3p5.(2P<3/2>).4f 2[9/2] → 3s2.3p5.(2P<3/2>).5g 2[11/2]*	Measured	NIST
440.6286 nm	700	Ca III	emission	3s2.3p5.(2P<1/2>).4d 2[5/2] → 3s2.3p5.(2P*<1/2>).4f 2[7/2]	Measured	NIST
451.6586 nm	700	Ca III	emission	3s2.3p5.(2P<1/2>).4d 2[3/2] → 3s2.3p5.(2P*<1/2>).4f 2[5/2]	Measured	NIST
457.2125 nm	700	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[5/2] → 3s2.3p5.(2P*<3/2>).4f 2[7/2]	Measured	NIST
424.0742 nm	600	Ca III	emission	3s2.3p5.(2P<3/2>).4f 2[9/2] → 3s2.3p5.(2P<3/2>).5g 2[11/2]*	Measured	NIST
443.129 nm	600	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[5/2] → 3s2.3p5.(2P*<3/2>).4f 2[7/2]	Measured	NIST
415.3566 nm	500	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[1/2] → 3s2.3p5.(2P*<3/2>).4f 2[3/2]	Measured	NIST
418.42 nm	500	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[1/2] → 3s2.3p5.(2P*<3/2>).4f 2[3/2]	Measured	NIST
428.4388 nm	500	Ca III	emission	3s2.3p5.(2P<1/2>).4f 2[7/2] → 3s2.3p5.(2P<1/2>).5g 2[9/2]*	Measured	NIST
432.9182 nm	490	Ca III	emission	3s2.3p5.(2P<3/2>).4f 2[7/2] → 3s2.3p5.(2P<3/2>).5g 2[9/2]*	Measured	NIST
433.3566 nm	480	Ca III	emission	3s2.3p5.(2P<3/2>).4f 2[7/2] → 3s2.3p5.(2P<3/2>).5g 2[9/2]*	Measured	NIST
416.4302 nm	430	Ca III	emission	3s2.3p5.(2P<3/2>).4f 2[3/2] → 3s2.3p5.(2P<3/2>).5g 2[5/2]*	Measured	NIST
417.565 nm	410	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[7/2] → 3s2.3p5.(2P*<3/2>).4f 2[7/2]	Measured	NIST
427.189 nm	410	Ca III	emission	3s2.3p5.(2P<1/2>).4f 2[5/2] → 3s2.3p5.(2P<1/2>).5g 2[7/2]*	Measured	NIST
435.8366 nm	410	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[3/2] → 3s2.3p5.(2P*<1/2>).4f 2[5/2]	Measured	NIST
421.3132 nm	400	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[1/2] → 3s2.3p5.(2P*<3/2>).4f 2[3/2]	Measured	NIST
413.6247 nm	390	Ca III	emission	3s2.3p5.(2P<3/2>).4f 2[3/2] → 3s2.3p5.(2P<3/2>).5g 2[5/2]*	Measured	NIST
427.9722 nm	360	Ca III	emission	3s2.3p5.(2P<1/2>).4f 2[7/2] → 3s2.3p5.(2P<1/2>).5g 2[9/2]*	Measured	NIST
430.1494 nm	290	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[3/2] → 3s2.3p5.(2P*<3/2>).4f 2[3/2]	Measured	NIST
429.0071 nm	280	Ca III	emission	3s2.3p5.(2P<3/2>).4f 2[5/2] → 3s2.3p5.(2P<3/2>).5g 2[7/2]*	Measured	NIST
427.8215 nm	270	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[7/2] → 3s2.3p5.(2P*<3/2>).4f 2[7/2]	Measured	NIST
430.101 nm	240	Ca III	emission	3s2.3p5.(2P<1/2>).4f 2[5/2] → 3s2.3p5.(2P<1/2>).5g 2[7/2]*	Measured	NIST
393.3663 nm	230	Ca II	emission	3p6.4s 2S → 3p6.4p 2P*	Measured	NIST
394.9609 nm	230	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[5/2] → 3s2.3p5.(2P*<1/2>).4f 2[7/2]	Measured	NIST
396.8469 nm	220	Ca II	emission	3p6.4s 2S → 3p6.4p 2P*	Measured	NIST
427.3875 nm	200	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[7/2] → 3s2.3p5.(2P*<3/2>).4f 2[7/2]	Measured	NIST
527.1979 nm	170	Ca III	emission	3s2.3p5.(2P<3/2>).5p 2[5/2] → 3s2.3p5.(2P<3/2>).5d 2[7/2]*	Measured	NIST
403.8502 nm	160	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[1/2] → 3s2.3p5.(2P*<3/2>).4f 2[5/2]	Measured	NIST
382.376 nm	150	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[7/2] → 3s2.3p5.(2P*<1/2>).4f 2[7/2]	Measured	NIST
448.4948 nm	150	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[5/2] → 3s2.3p5.(2P*<3/2>).4f 2[5/2]	Measured	NIST
470.8836 nm	150	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[5/2] → 3s2.3p5.(2P*<3/2>).4f 2[5/2]	Measured	NIST
471.6287 nm	130	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[5/2] → 3s2.3p5.(2P*<3/2>).4f 2[9/2]	Measured	NIST
606.9998 nm	110	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[7/2] → 3s2.3p5.(2P*<3/2>).5p 2[5/2]	Measured	NIST
524.7373 nm	100	Ca III	emission	3s2.3p5.(2P<3/2>).5p 2[5/2] → 3s2.3p5.(2P<3/2>).5d 2[7/2]*	Measured	NIST
393.0884 nm	90	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[5/2] → 3s2.3p5.(2P*<1/2>).4f 2[5/2]	Measured	NIST
485.9165 nm	90	Ca III	emission	3s2.3p5.(2P<3/2>).5p 2[5/2] → 3s2.3p5.(2P<3/2>).6s 2[3/2]*	Measured	NIST
500.8939 nm	90	Ca III	emission	3s2.3p5.(2P<3/2>).5p 2[1/2] → 3s2.3p5.(2P<3/2>).5d 2[1/2]*	Measured	NIST
532.1287 nm	90	Ca III	emission	3s2.3p5.(2P<3/2>).5p 2[3/2] → 3s2.3p5.(2P<3/2>).5d 2[5/2]*	Measured	NIST
434.0345 nm	80	Ca III	emission	3s2.3p5.(2P<3/2>).4f 2[7/2] → 3s2.3p5.(2P<3/2>).5g 2[7/2]*	Measured	NIST
441.3732 nm	80	Ca III	emission	3s2.3p5.(2P<1/2>).4d 2[5/2] → 3s2.3p5.(2P*<1/2>).4f 2[5/2]	Measured	NIST
450.8788 nm	80	Ca III	emission	3s2.3p5.(2P<1/2>).4d 2[3/2] → 3s2.3p5.(2P*<1/2>).4f 2[7/2]	Measured	NIST
463.2855 nm	80	Ca III	emission	3s2.3p5.(2P<1/2>).5p 2[3/2] → 3s2.3p5.(2P<1/2>).5d 2[3/2]*	Measured	NIST
501.9971 nm	80	Ca II	emission	3p6.5p 2P* → 3p6.6d 2D	Measured	NIST
505.0089 nm	80	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[3/2] → 3s2.3p5.(2P*<3/2>).4f 2[5/2]	Measured	NIST
557.0601 nm	80	Ca III	emission	3s2.3p5.(2P<3/2>).4d 2[3/2] → 3s2.3p5.(2P*<3/2>).5p 2[3/2]	Measured	NIST

Extended Properties

Covalent Radii (Extended)

Covalent radius (Pyykkö)

Covalent radius (Pyykkö, double)

Covalent radius (Pyykkö, triple)

Covalent radius (Bragg)

Van der Waals Radii

Truhlar

Batsanov

Alvarez

UFF

MM3

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

Supply Risk & Economics

Production concentration

Relative supply risk

Political stability (top producer)

Phase Transitions & Allotropes

Melting point	1115.15 K
Boiling point	1757.15 K

Oxidation State Categories

+1 extended

+2 main

Advanced Reference Data

Screening Constants (6)

n	Orbital	σ
1	s	0.527
2	p	3.9586
2	s	6.2236
3	p	11.3417
3	s	10.3985
4	s	15.602

Crystal Radii Detail (6)

Charge	CN	r_crystal (pm)	Origin
2	VI	114
2	VII	120
2	VIII	126
2	IX	132
2	X	137	calculated,
2	XII	148	calculated,

Isotope Decay Modes (50)

Isotope	Mode	Intensity
33	p	—
34	2p	—
35	B+	100%
35	B+p	95.8%
35	2p	4.2%
36	B+	100%
36	B+p	51.2%
37	B+	100%
37	B+p	76.8%
38	B+	100%

X‑ray Scattering Factors (504)

Energy (eV)	f₁	f₂
10	—	0.0428
10.1617	—	0.04527
10.3261	—	0.04788
10.4931	—	0.05063
10.6628	—	0.05355
10.8353	—	0.05663
11.0106	—	0.05989
11.1886	—	0.06334
11.3696	—	0.06634
11.5535	—	0.06922

Additional Data

Estimated Crustal Abundance

The estimated element abundance in the earth's crust.

4.15×104 milligrams per kilogram

References (1)

[5] Calcium https://education.jlab.org/itselemental/ele020.html

Estimated Oceanic Abundance

The estimated element abundance in the earth's oceans.

4.12×102 milligrams per liter

References (1)

[5] Calcium https://education.jlab.org/itselemental/ele020.html

Sources

Sources of this element.

Calcium, a metallic element, is fifth in abundance in the earth's crust, of which it forms more than 3%. It is an essential constituent of leaves, bones, teeth, and shells. Never found in nature uncombined, it occurs abundantly as limestone, gypsum, and fluorite. Apatite is the fluorophosphate or chlorophosphate of calcium.

References (1)

[6] Calcium https://periodic.lanl.gov/20.shtml

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)

Calcium

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

Calcium

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

Calcium

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

Calcium

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

Calcium

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

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9 PubChem Elements

Calcium

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.