For elements that are solid at standard temperature and pressure the first table gives the crystalline structure of the most thermodynamically stable form(s) in those conditions. Each element is shaded by a color representing its respective Bravais lattice, except that all orthorhombic lattices are grouped together.
Crystal structure of elements in the periodic table at standard temperature and pressure [1] | |||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 H | 2 He | ||||||||||||||||||
3 Li W | 4 Be Mg | 5 B β-B | 6 C g-C | 7 N | 8 O | 9 F | 10 Ne | ||||||||||||
11 Na W | 12 Mg Mg | 13 Al Cu | 14 Si d-C | 15 P b-P | 16 S α-S | 17 Cl | 18 Ar | ||||||||||||
19 K W | 20 Ca Cu | 21 Sc Mg | 22 Ti Mg | 23 V W | 24 Cr W | 25 Mn α-Mn | 26 Fe W | 27 Co Mg | 28 Ni Cu | 29 Cu Cu | 30 Zn Mg | 31 Ga α-Ga | 32 Ge d-C | 33 As α-As | 34 Se γ-Se | 35 Br | 36 Kr | ||
37 Rb W | 38 Sr Cu | 39 Y Mg | 40 Zr Mg | 41 Nb W | 42 Mo W | 43 Tc Mg | 44 Ru Mg | 45 Rh Cu | 46 Pd Cu | 47 Ag Cu | 48 Cd Mg | 49 In In | 50 Sn β-Sn | 51 Sb α-As | 52 Te γ-Se | 53 I Cl | 54 Xe | ||
55 Cs W | 56 Ba W | 71 Lu Mg | 72 Hf Mg | 73 Ta W | 74 W W | 75 Re Mg | 76 Os Mg | 77 Ir Cu | 78 Pt Cu | 79 Au Cu | 80 Hg | 81 Tl Mg | 82 Pb Cu | 83 Bi α-As | 84 Po α-Po | 85 At | 86 Rn | ||
87 Fr | 88 Ra W | 103 Lr | 104 Rf | 105 Db | 106 Sg | 107 Bh | 108 Hs | 109 Mt | 110 Ds | 111 Rg | 112 Cn | 113 Nh | 114 Fl | 115 Mc | 116 Lv | 117 Ts | 118 Og | ||
57 La α-La | 58 Ce α-La | 59 Pr α-La | 60 Nd α-La | 61 Pm α-La | 62 Sm α-Sm | 63 Eu W | 64 Gd Mg | 65 Tb Mg | 66 Dy Mg | 67 Ho Mg | 68 Er Mg | 69 Tm Mg | 70 Yb Cu | ||||||
89 Ac Cu | 90 Th Cu | 91 Pa α-Pa | 92 U α-U | 93 Np α-Np | 94 Pu α-Pu | 95 Am α-La | 96 Cm α-La | 97 Bk α-La | 98 Cf α-La | 99 Es Cu | 100 Fm | 101 Md | 102 No |
Legend: |
---|
Not solid at standard temperature and pressure or uncertain |
The second table gives the most stable structure of each element at its melting point. (H, He, N, O, F, Ne, Cl, Ar, Kr, Xe, and Rn are gases at STP; Br and Hg are liquids at STP.) Note that helium does not have a melting point at atmospheric pressure, but it adopts a magnesium-type hexagonal close-packed structure under high pressure.
Crystal structures of elements at their melting points at atmospheric pressure | |||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 H 13 K Mg | 2 He * | ||||||||||||||||||
3 Li 453 K W | 4 Be 1560 K W | 5 B 2349 K β-B | 6 C 3800 K g-C | 7 N 63 K β-N | 8 O 54 K γ-O | 9 F 53 K γ-O | 10 Ne 24 K Cu | ||||||||||||
11 Na 370 K W | 12 Mg 923 K Mg | 13 Al 933 K Cu | 14 Si 1687 K d-C | 15 P 883 K b-P | 16 S 393 K β-S | 17 Cl 171 K Cl | 18 Ar 83 K Cu | ||||||||||||
19 K 336 K W | 20 Ca 1115 K W | 21 Sc 1814 K W | 22 Ti 1941 K W | 23 V 2183 K W | 24 Cr 2180 K W | 25 Mn 1519 K W | 26 Fe 1811 K W | 27 Co 1768 K Cu | 28 Ni 1728 K Cu | 29 Cu 1357 K Cu | 30 Zn 692 K Mg | 31 Ga 302 K α-Ga | 32 Ge 1211 K d-C | 33 As 1090 K b-P | 34 Se 494 K γ-Se | 35 Br 265 K Cl | 36 Kr 115 K Cu | ||
37 Rb 312 K W | 38 Sr 1050 K W | 39 Y 1799 K W | 40 Zr 2128 K W | 41 Nb 2750 K W | 42 Mo 2896 K W | 43 Tc 2430 K Mg | 44 Ru 2607 K Mg | 45 Rh 2237 K Cu | 46 Pd 1828 K Cu | 47 Ag 1234 K Cu | 48 Cd 594 K Mg | 49 In 429 K In | 50 Sn 505 K β-Sn | 51 Sb 903 K α-As | 52 Te 722 K γ-Se | 53 I 386 K Cl | 54 Xe 161 K Cu | ||
55 Cs 301 K W | 56 Ba 1000 K W | 71 Lu 1925 K Mg | 72 Hf 2506 K W | 73 Ta 3290 K W | 74 W 3695 K W | 75 Re 3459 K Mg | 76 Os 3306 K Mg | 77 Ir 2719 K Cu | 78 Pt 2041 K Cu | 79 Au 1337 K Cu | 80 Hg 234 K α-Hg | 81 Tl 557 K W | 82 Pb 600 K Cu | 83 Bi 544 K α-As | 84 Po 527 K β-Po | 85 At 575 K? ? | 86 Rn 202 K ? | ||
87 Fr 281 K? ? | 88 Ra 973 K W | 103 Lr 1900 K? ? | 104 Rf ? | 105 Db ? | 106 Sg ? | 107 Bh ? | 108 Hs ? | 109 Mt ? | 110 Ds ? | 111 Rg ? | 112 Cn ? | 113 Nh ? | 114 Fl ? | 115 Mc ? | 116 Lv ? | 117 Ts ? | 118 Og ? | ||
57 La 1193 K W | 58 Ce 1068 K W | 59 Pr 1208 K W | 60 Nd 1297 K W | 61 Pm 1315 K W | 62 Sm 1345 K W | 63 Eu 1099 K W | 64 Gd 1585 K W | 65 Tb 1629 K W | 66 Dy 1680 K W | 67 Ho 1734 K Mg | 68 Er 1802 K Mg | 69 Tm 1818 K Mg | 70 Yb 1097 K W | ||||||
89 Ac 1323 K Cu | 90 Th 2115 K W | 91 Pa 1841 K W | 92 U 1405 K W | 93 Np 917 K W | 94 Pu 912 K W | 95 Am 1449 K W | 96 Cm 1613 K Cu | 97 Bk 1259 K Cu | 98 Cf 1173 K Cu | 99 Es 1133 K Cu | 100 Fm 1800 K? ? | 101 Md 1100 K? ? | 102 No 1100 K? ? |
Legend: |
---|
unknown or uncertain |
Predictions are given for elements 85–87, 100–113 and 118; all but radon [2] have not been produced in bulk. Probably Cn and Fl are liquids at STP. Calculations have difficulty replicating the experimentally known bcc structures of the stable alkali metals, and the same problem affects Fr (87); [3] nonetheless, it is probably also bcc. [4] The latest predictions for Fl (114) could not distinguish between face-centred cubic and hexagonal close-packed structures, which were predicted to be close in energy. [5] No predictions are available for elements 115–117.
Predicted crystal structures of highly unstable elements | |||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 H | 2 He | ||||||||||||||||||
3 Li | 4 Be | 5 B | 6 C | 7 N | 8 O | 9 F | 10 Ne | ||||||||||||
11 Na | 12 Mg | 13 Al | 14 Si | 15 P | 16 S | 17 Cl | 18 Ar | ||||||||||||
19 K | 20 Ca | 21 Sc | 22 Ti | 23 V | 24 Cr | 25 Mn | 26 Fe | 27 Co | 28 Ni | 29 Cu | 30 Zn | 31 Ga | 32 Ge | 33 As | 34 Se | 35 Br | 36 Kr | ||
37 Rb | 38 Sr | 39 Y | 40 Zr | 41 Nb | 42 Mo | 43 Tc | 44 Ru | 45 Rh | 46 Pd | 47 Ag | 48 Cd | 49 In | 50 Sn | 51 Sb | 52 Te | 53 I | 54 Xe | ||
55 Cs | 56 Ba | 71 Lu | 72 Hf | 73 Ta | 74 W | 75 Re | 76 Os | 77 Ir | 78 Pt | 79 Au | 80 Hg | 81 Tl | 82 Pb | 83 Bi | 84 Po | 85 At [Cu] [6] | 86 Rn [Cu] [7] | ||
87 Fr [W] [4] | 88 Ra | 103 Lr [Mg] [8] | 104 Rf [Mg] [8] | 105 Db [W] [8] | 106 Sg [W] [8] | 107 Bh [Mg] [8] | 108 Hs [Mg] [9] | 109 Mt [Cu] [8] | 110 Ds [W] [8] | 111 Rg [W] [8] | 112 Cn [Mg] [10] | 113 Nh [Mg] [11] | 114 Fl | 115 Mc | 116 Lv | 117 Ts | 118 Og [Cu] [7] | ||
57 La | 58 Ce | 59 Pr | 60 Nd | 61 Pm | 62 Sm | 63 Eu | 64 Gd | 65 Tb | 66 Dy | 67 Ho | 68 Er | 69 Tm | 70 Yb | ||||||
89 Ac | 90 Th | 91 Pa | 92 U | 93 Np | 94 Pu | 95 Am | 96 Cm | 97 Bk | 98 Cf | 99 Es | 100 Fm [Cu] [12] | 101 Md [Cu] [12] | 102 No [Cu] [12] |
Legend: |
---|
[…] predicted structure |
Elements with known structure. |
unknown or uncertain |
The following is a list of structure types which appear in the tables above. Regarding the number of atoms in the unit cell, structures in the rhombohedral lattice system have a rhombohedral primitive cell and have trigonal point symmetry but are also often also described in terms of an equivalent but nonprimitive hexagonal unit cell with three times the volume and three times the number of atoms.
Prototype | Strukturbericht | Diagram | Lattice system | Space group | Atoms per unit cell | Coordination | notes |
---|---|---|---|---|---|---|---|
α-Pu | (none) | Monoclinic | P21/m (No. 11) | 16 | slightly distorted hexagonal structure. Lattice parameters: a = 618.3 pm, b = 482.2 pm, c = 1096.3 pm, β = 101.79° [13] [14] | ||
β-S | (none) | Monoclinic | P21/c (No. 14) | 32 | |||
α-Np | Ac | Orthorhombic | Pnma (No. 62) | 8 | highly distorted bcc structure. Lattice parameters: a = 666.3 pm, b = 472.3 pm, c = 488.7 pm [15] [16] | ||
α-U | A20 | Orthorhombic | Cmcm (No. 63) | 4 | Each atom has four near neighbours, 2 at 275.4 pm, 2 at 285.4 pm. The next four at distances 326.3 pm and four more at 334.2 pm. [17] | Strongly distorted hcp structure. | |
α-Ga | A11 | Orthorhombic | Cmce (No. 64) | 8 | each Ga atom has one nearest neighbour at 244 pm, 2 at 270 pm, 2 at 273 pm, 2 at 279 pm. [18] | The structure is related to that of iodine. | |
b-P | A17 | Orthorhombic | Cmce (No. 64) | 8 | Specifically the black phosphorus form of phosphorus. | ||
Cl | A14 | Orthorhombic | Cmce (No. 64) | 8 | |||
α-S | A16 | Orthorhombic | Fddd (No. 70) | 16 | |||
In | A6 | Tetragonal | I4/mmm (No. 139) | 2 | Identical symmetry to the α-Pa type structure. Can be considered slightly distorted from an ideal Cu type face-centered cubic structure [18] which has . | ||
α-Pa | Aa | Tetragonal | I4/mmm (No. 139) | 2 | Identical symmetry to the In type structure. Can be considered slightly distorted from an ideal W type body centered cubic structure which has . | ||
β-Sn | A5 | Tetragonal | I41/amd (No. 141) | 4 | 4 neighbours at 302 pm; 2 at 318 pm; 4 at 377 pm; 8 at 441 pm [18] | white tin form (thermodynamical stable above 286.4 K) | |
β-B | (none) | Rhombohedral | R3m (No. 166) | 105 (rh.) 315 (hex.) | Partly due to its complexity, whether this structure is the ground state of Boron has not been fully settled. | ||
α-As | A7 | Rhombohedral | R3m (No. 166) | 2 (rh.) 6 (hex.) | in grey metallic form, each As atom has 3 neighbours in the same sheet at 251.7pm; 3 in adjacent sheet at 312.0 pm. [18] each Bi atom has 3 neighbours in the same sheet at 307.2 pm; 3 in adjacent sheet at 352.9 pm. [18] each Sb atom has 3 neighbours in the same sheet at 290.8pm; 3 in adjacent sheet at 335.5 pm. [18] | puckered sheet | |
α-Sm | (none) | Rhombohedral | R3m (No. 166) | 3 (rh.) 9 (hex.) | 12 nearest neighbours | complex hcp with 9-layer repeat: ABCBCACAB.... [19] | |
α-Hg | A10 | Rhombohedral | R3m (No. 166) | 1 (rh.) 3 (hex.) | 6 nearest neighbours at 234 K and 1 atm (it is liquid at room temperature and thus has no crystal structure at ambient conditions!) | Identical symmetry to the β-Po structure, distinguished based on details about the basis vectors of its unit cell. This structure can also be considered to be a distorted hcp lattice with the nearest neighbours in the same plane being approx 16% farther away [18] | |
β-Po | Ai | Rhombohedral | R3m (No. 166) | 1 (rh.) 3 (hex.) | Identical symmetry to the α-Hg structure, distinguished based on details about the basis vectors of its unit cell. | ||
γ-Se | A8 | Hexagonal | P321 (No. 154) | 3 | |||
Mg | A3 | Hexagonal | P63/mmc (No. 194) | 2 | Zn has 6 nearest neighbors in same plane: 6 in adjacent planes 14% farther away [18] Cd has 6 nearest neighbours in the same plane- 6 in adjacent planes 15% farther away [18] | If the unit cell axial ratio is exactly the structure would be a mathematical hexagonal close packed (HCP) structure. However, in real materials there are deviations from this in some metals where the unit cell is distorted in one direction but the structure still retains the hcp space group—remarkable all the elements have a ratio of lattice parameters c/a < 1.633 (best are Mg and Co and worst Be with c/a ~ 1.568). In others like Zn and Cd the deviations from the ideal change the symmetry of the structure and these have a lattice parameter ratio c/a > 1.85. | |
g-C | A9 | Hexagonal | P63/mmc (No. 194) | 4 | Specifically the graphite form of carbon. | ||
α-La | A3' | Hexagonal | P63/mmc (No. 194) | 4 | The Double hexagonal close packed (DHCP) structure. Similar to the ideal hcp structure, the perfect dhcp structure should have a lattice parameter ratio of In the real dhcp structures of 5 lanthanides (including β-Ce) variates between 1.596 (Pm) and 1.6128 (Nd). For the four known actinides dhcp lattices the corresponding number vary between 1.620 (Bk) and 1.625 (Cf). [20] | ||
β-N | (none) | Hexagonal | P63/mmc (No. 194) | 4 | |||
α-Po | Ah | Cubic | Pm3m (No. 221) | 1 | 6 nearest neighbours | simple cubic lattice. The atoms in the unit cell are at the corner of a cube. | |
γ-O | (none) | Cubic | Pm3n (No. 223) | 16 | Closely related to the β-W structure, except with a diatomic oxygen molecule in place of each tungsten atom. The molecules can rotate in place, but the direction of rotation for some of the molecules is restricted. | ||
α-Mn | A12 | Cubic | I43m (No. 217) | 58 | Unit cell contains Mn atoms in 4 different environments. [18] | Distorted bcc | |
W | A2 | Cubic | Im3m (No. 229) | 2 | The Body centered cubic structure (BCC). It is not a close packed structure. In this each metal atom is at the centre of a cube with 8 nearest neighbors, however the 6 atoms at the centres of the adjacent cubes are only approximately 15% further away so the coordination number can therefore be considered to be 14 when these are on one 4 fold axe structure becomes face-centred cubic (cubic close packed). | ||
Cu | A1 | Cubic | Fm3m (No. 225) | 4 | The face-centered cubic (cubic close packed) structure. More content relating to number of planes within structure and implications for glide/slide e.g. ductility. | ||
d-C | A4 | Cubic | Fd3m (No. 227) | 8 | The diamond cubic (DC) structure. Specifically the diamond form of Carbon. |
The observed crystal structures of many metals can be described as a nearly mathematical close-packing of equal spheres. A simple model for both of these is to assume that the metal atoms are spherical and are packed together as closely as possible. In closest packing, every atom has 12 equidistant nearest neighbours, and therefore a coordination number of 12. If the close packed structures are considered as being built of layers of spheres, then the difference between hexagonal close packing and face-centred cubic is how each layer is positioned relative to others. The following types can be viewed as a regular buildup of close-packed layers:
Precisely speaking, the structures of many of the elements in the groups above are slightly distorted from the ideal closest packing. While they retain the lattice symmetry as the ideal structure, they often have nonideal c/a ratios for their unit cell. Less precisely speaking, there are also other elements are nearly close-packed but have distortions which have at least one broken symmetry with respect to the close-packed structure:
Berkelium is a synthetic chemical element; it has symbol Bk and atomic number 97. It is a member of the actinide and transuranium element series. It is named after the city of Berkeley, California, the location of the Lawrence Berkeley National Laboratory where it was discovered in December 1949. Berkelium was the fifth transuranium element discovered after neptunium, plutonium, curium and americium.
A chemical element is a chemical substance that cannot be broken down into other substances by chemical reactions. The basic particle that constitutes a chemical element is the atom. Chemical elements are identified by the number of protons in the nuclei of their atoms, known as the element's atomic number. For example, oxygen has an atomic number of 8, meaning that each oxygen atom has 8 protons in its nucleus. Two or more atoms of the same element can combine to form molecules, in contrast to chemical compounds or mixtures, which contain atoms of different elements. Atoms can be transformed into different elements in nuclear reactions, which change an atom's atomic number.
Curium is a synthetic chemical element; it has symbol Cm and atomic number 96. This transuranic actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first intentionally made by the team of Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso in 1944, using the cyclotron at Berkeley. They bombarded the newly discovered element plutonium with alpha particles. This was then sent to the Metallurgical Laboratory at University of Chicago where a tiny sample of curium was eventually separated and identified. The discovery was kept secret until after the end of World War II. The news was released to the public in November 1947. Most curium is produced by bombarding uranium or plutonium with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains ~20 grams of curium.
Californium is a synthetic chemical element; it has symbol Cf and atomic number 98. It was first synthesized in 1950 at Lawrence Berkeley National Laboratory by bombarding curium with alpha particles. It is an actinide element, the sixth transuranium element to be synthesized, and has the second-highest atomic mass of all elements that have been produced in amounts large enough to see with the naked eye. It was named after the university and the U.S. state of California.
In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece.
Lawrencium is a synthetic chemical element; it has symbol Lr and atomic number 103. It is named in honor of Ernest Lawrence, inventor of the cyclotron, a device that was used to discover many artificial radioactive elements. A radioactive metal, lawrencium is the eleventh transuranic element and the last member of the actinide series. Like all elements with atomic number over 100, lawrencium can only be produced in particle accelerators by bombarding lighter elements with charged particles. Fourteen isotopes of lawrencium are currently known; the most stable is 266Lr with half-life 11 hours, but the shorter-lived 260Lr is most commonly used in chemistry because it can be produced on a larger scale.
The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows ("periods") and columns ("groups"). It is an icon of chemistry and is widely used in physics and other sciences. It is a depiction of the periodic law, which states that when the elements are arranged in order of their atomic numbers an approximate recurrence of their properties is evident. The table is divided into four roughly rectangular areas called blocks. Elements in the same group tend to show similar chemical characteristics.
Protactinium is a chemical element; it has symbol Pa and atomic number 91. It is a dense, radioactive, silvery-gray actinide metal which readily reacts with oxygen, water vapor, and inorganic acids. It forms various chemical compounds, in which protactinium is usually present in the oxidation state +5, but it can also assume +4 and even +3 or +2 states. Concentrations of protactinium in the Earth's crust are typically a few parts per trillion, but may reach up to a few parts per million in some uraninite ore deposits. Because of its scarcity, high radioactivity, and high toxicity, there are currently no uses for protactinium outside scientific research, and for this purpose, protactinium is mostly extracted from spent nuclear fuel.
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter.
Group 4 is the second group of transition metals in the periodic table. It contains the four elements titanium (Ti), zirconium (Zr), hafnium (Hf), and rutherfordium (Rf). The group is also called the titanium group or titanium family after its lightest member.
In crystallography, the cubiccrystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.
In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement. Carl Friedrich Gauss proved that the highest average density – that is, the greatest fraction of space occupied by spheres – that can be achieved by a lattice packing is
A uranate is a ternary oxide involving the element uranium in one of the oxidation states 4, 5 or 6. A typical chemical formula is MxUyOz, where M represents a cation. The uranium atom in uranates(VI) has two short collinear U–O bonds and either four or six more next nearest oxygen atoms. The structures are infinite lattice structures with the uranium atoms linked by bridging oxygen atoms.
In chemistry, crystallography, and materials science, the coordination number, also called ligancy, of a central atom in a molecule or crystal is the number of atoms, molecules or ions bonded to it. The ion/molecule/atom surrounding the central ion/molecule/atom is called a ligand. This number is determined somewhat differently for molecules than for crystals.
In materials science, an interstitial defect is a type of point crystallographic defect where an atom of the same or of a different type, occupies an interstitial site in the crystal structure. When the atom is of the same type as those already present they are known as a self-interstitial defect. Alternatively, small atoms in some crystals may occupy interstitial sites, such as hydrogen in palladium. Interstitials can be produced by bombarding a crystal with elementary particles having energy above the displacement threshold for that crystal, but they may also exist in small concentrations in thermodynamic equilibrium. The presence of interstitial defects can modify the physical and chemical properties of a material.
Many compound materials exhibit polymorphism, that is they can exist in different structures called polymorphs. Silicon carbide (SiC) is unique in this regard as more than 250 polymorphs of silicon carbide had been identified by 2006, with some of them having a lattice constant as long as 301.5 nm, about one thousand times the usual SiC lattice spacings.
In crystallography, the hexagonal crystal family is one of the 6 crystal families, which includes two crystal systems and two lattice systems. While commonly confused, the trigonal crystal system and the rhombohedral lattice system are not equivalent. In particular, there are crystals that have trigonal symmetry but belong to the hexagonal lattice.
Ammonium fluorosilicate (also known as ammonium hexafluorosilicate, ammonium fluosilicate or ammonium silicofluoride) has the formula (NH4)2SiF6. It is a toxic chemical, like all salts of fluorosilicic acid. It is made of white crystals, which have at least three polymorphs and appears in nature as rare minerals cryptohalite or bararite.
Berkelium forms a number of chemical compounds, where it normally exists in an oxidation state of +3 or +4, and behaves similarly to its lanthanide analogue, terbium. Like all actinides, berkelium easily dissolves in various aqueous inorganic acids, liberating gaseous hydrogen and converting into the trivalent oxidation state. This trivalent state is the most stable, especially in aqueous solutions, but tetravalent berkelium compounds are also known. The existence of divalent berkelium salts is uncertain and has only been reported in mixed lanthanum chloride-strontium chloride melts. Aqueous solutions of Bk3+ ions are green in most acids. The color of the Bk4+ ions is yellow in hydrochloric acid and orange-yellow in sulfuric acid. Berkelium does not react rapidly with oxygen at room temperature, possibly due to the formation of a protective oxide surface layer; however, it reacts with molten metals, hydrogen, halogens, chalcogens and pnictogens to form various binary compounds. Berkelium can also form several organometallic compounds.
Iron–hydrogen alloy, also known as iron hydride, is an alloy of iron and hydrogen and other elements. Because of its lability when removed from a hydrogen atmosphere, it has no uses as a structural material.