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Se Selenium
Element Information, Facts, Properties, Trends, Uses, Comparison with other elements

34
Se
Selenium
Element 34 of Periodic table is Selenium with atomic number 34, atomic weight 78.96. Selenium, symbol Se, has a Simple Monoclinic structure and Gray color. Selenium is a Other Nonmetal element. It is part of group 16 (oxygen family). Know everything about Selenium Facts, Physical Properties, Chemical Properties, Electronic configuration, Atomic and Crystal Structure.
34 Se - Selenium | SchoolMyKids

Selenium is a chemical element with symbol Se and atomic number 34. It is a nonmetal with properties that are intermediate between those of its periodic table column-adjacent chalcogen elements sulfur and tellurium. It rarely occurs in its elemental state in nature, or as pure ore compounds.

It belongs to group 16 of the periodic table having trivial name chalcogens.

Selenium Facts

Read key information and facts about element Selenium

NameSelenium
Atomic Number34
Atomic SymbolSe
Atomic Weight78.96
PhaseSolid
ColorGray
Appearanceblack, red, and gray (not pictured) allotropes
ClassificationOther Nonmetal
Group in Periodic Table16
Group Nameoxygen family
Period in Periodic Tableperiod 4
Block in Periodic Tablep -block
Electronic Configuration[Ar] 3d10 4s2 4p4
Electronic Shell Structure (Electrons per shell)2, 8, 18, 6
Melting Point494 K
Boiling Point958 K
CAS NumberCAS7782-49-2
123456789101112131415161718
1
1
H
Hydrogen
1.008

Atomic #

Electronic Shell #

Symbol
Name
Atomic Weight
HGas
HgLiquid
CSolid
Metals
Metalloids
NonMetals
Alkali metals
Alkali earth metals
Lanthanoids
Transition metals
Post-transition metals
Other nonmetals
Halogens
Nobel gas
Actinoids
2
He
Helium
4.003
2
3
Li
Lithium
6.941
4
Be
Beryllium
9.012
5
B
Boron
10.811
6
C
Carbon
12.011
7
N
Nitrogen
14.007
8
O
Oxygen
15.999
9
F
Fluorine
18.998
10
Ne
Neon
20.180
3
11
Na
Sodium
22.990
12
Mg
Magnesium
24.305
13
Al
Aluminium
26.982
14
Si
Silicon
28.085
15
P
Phosphorus
30.974
16
S
Sulfur
32.065
17
Cl
Chlorine
35.453
18
Ar
Argon
39.948
4
19
K
Potassium
39.098
20
Ca
Calcium
40.078
21
Sc
Scandium
44.956
22
Ti
Titanium
47.867
23
V
Vanadium
50.941
24
Cr
Chromium
51.996
25
Mn
Manganese
54.938
26
Fe
Iron
55.845
27
Co
Cobalt
58.933
28
Ni
Nickel
58.693
29
Cu
Copper
63.546
30
Zn
Zinc
65.409
31
Ga
Gallium
69.723
32
Ge
Germanium
72.640
33
As
Arsenic
74.922
34
Se
Selenium
78.960
35
Br
Bromine
79.904
36
Kr
Krypton
83.798
5
37
Rb
Rubidium
85.468
38
Sr
Strontium
87.620
39
Y
Yttrium
88.906
40
Zr
Zirconium
91.224
41
Nb
Niobium
92.906
42
Mo
Molybdenum
95.940
43
Tc
Technetium
98
44
Ru
Ruthenium
101.070
45
Rh
Rhodium
102.906
46
Pd
Palladium
106.420
47
Ag
Silver
107.868
48
Cd
Cadmium
112.411
49
In
Indium
114.818
50
Sn
Tin
118.710
51
Sb
Antimony
121.760
52
Te
Tellurium
127.600
53
I
Iodine
126.904
54
Xe
Xenon
131.293
6
55
Cs
Cesium
132.905
56
Ba
Barium
137.327
57 - 71
La - Lu
Lanthanides
72
Hf
Hafnium
178.490
73
Ta
Tantalum
180.948
74
W
Tungsten
183.840
75
Re
Rhenium
186.207
76
Os
Osmium
190.230
77
Ir
Iridium
192.217
78
Pt
Platinum
195.078
79
Au
Gold
196.967
80
Hg
Mercury
200.590
81
Tl
Thallium
204.383
82
Pb
Lead
207.200
83
Bi
Bismuth
208.980
84
Po
Polonium
209
85
At
Astatine
210
86
Rn
Radon
222
7
87
Fr
Francium
223
88
Ra
Radium
226
89 - 103
Ac - Lr
Actinides
104
Rf
Rutherfordium
261
105
Db
Dubnium
262
106
Sg
Seaborgium
266
107
Bh
Bohrium
264
108
Hs
Hassium
277
109
Mt
Meitnerium
268
110
Ds
Darmstadtium
281
111
Rg
Roentgenium
272
112
Cn
Copernicium
285
113
Nh
Nihonium
284
114
Fl
Flerovium
289
115
Mc
Moscovium
288
116
Lv
Livermorium
292
117
Ts
Tennessine
294
118
Og
Oganesson
294
Lanthanides
57
La
Lanthanum
138.905
58
Ce
Cerium
140.116
59
Pr
Praseodymium
140.908
60
Nd
Neodymium
144.240
61
Pm
Promethium
145
62
Sm
Samarium
150.360
63
Eu
Europium
151.964
64
Gd
Gadolinium
157.250
65
Tb
Terbium
158.925
66
Dy
Dysprosium
162.500
67
Ho
Holmium
164.930
68
Er
Erbium
167.259
69
Tm
Thulium
168.934
70
Yb
Ytterbium
173.040
71
Lu
Lutetium
174.967
Actinides
89
Ac
Actinium
227
90
Th
Thorium
232.038
91
Pa
Protactinium
231.036
92
U
Uranium
238.029
93
Np
Neptunium
237
94
Pu
Plutonium
244
95
Am
Americium
243
96
Cm
Curium
247
97
Bk
Berkelium
247
98
Cf
Californium
251
99
Es
Einsteinium
252
100
Fm
Fermium
257
101
Md
Mendelevium
258
102
No
Nobelium
259
103
Lr
Lawrencium
262

How to Locate Selenium on Periodic Table

Periodic table is arranged by atomic number, number of protons in the nucleus which is same as number of electrons. The atomic number increases from left to right. Periodic table starts at top left ( Atomic number 1) and ends at bottom right (atomic number 118). Therefore you can directly look for atomic number 34 to find Selenium on periodic table.

Another way to read periodic table and locate an element is by using group number (column) and period number (row). To locate Selenium on periodic table look for cross section of group 16 and period 4 in the modern periodic table.

Selenium History

The element Selenium was discovered by J. Berzelius and G. Gahn in year 1817 in Sweden. Selenium was first isolated by J. Berzelius and G. Gahn in 1817. Selenium derived its name from the Greek selene, meaning 'moon'.

While working with lead they discovered a substance that they thought was tellurium, but realized after more investigation that it is different.

Selenium Presence: Abundance in Nature and Around Us

The table below shows the abundance of Selenium in Universe, Sun, Meteorites, Earth's Crust, Oceans and Human Body.

 ppb by weight (1ppb =10^-7 %)ppb by atoms (1ppb =10^-7 %)
Abundance in Universe300.5
Abundance in Sun--
Abundance in Meteorites130002900
Abundance in Earth's Crust5010
Abundance in Oceans0.450.035
Abundance in Humans504

Crystal Structure of Selenium

The solid state structure of Selenium is Simple Monoclinic.

The Crystal structure can be described in terms of its unit Cell. The unit Cells repeats itself in three dimensional space to form the structure.

Unit Cell Parameters

The unit cell is represented in terms of its lattice parameters, which are the lengths of the cell edges Lattice Constants (a, b and c)

abc
905.4 pm908.3 pm1160.1 pm

and the angles between them Lattice Angles (alpha, beta and gamma).

alphabetagamma
π/2 1.58493 π/2

The positions of the atoms inside the unit cell are described by the set of atomic positions ( xi, yi, zi) measured from a reference lattice point.

The symmetry properties of the crystal are described by the concept of space groups. All possible symmetric arrangements of particles in three-dimensional space are described by the 230 space groups (219 distinct types, or 230 if chiral copies are considered distinct.

Space Group NameP121/c1 34 Se Selenium - Crystal Structure | SchoolMyKids
Oxidation StatesSpace Group Number14
Crystal StructureSimple Monoclinic

Selenium Atomic and Orbital Properties

Selenium atoms have 34 electrons and the electronic shell structure is [2, 8, 18, 6] with Atomic Term Symbol (Quantum Numbers) 3P2.

Atomic Number34
Number of Electrons (with no charge)34
Number of Protons34
Mass Number79
Number of Neutrons45
Shell structure (Electrons per energy level)2, 8, 18, 6
Electron Configuration[Ar] 3d10 4s2 4p4
Valence Electrons4s2 4p4
Valence (Valency)6
Main Oxidation States-2, 2, 4, 6
Oxidation States-2, -1, 0, 1, 2, 3, 4, 5, 6
Atomic Term Symbol (Quantum Numbers)3P2

Bohr Atomic Model of Selenium - Electrons per energy level

34 Se Selenium - Electron Shell Structure | SchoolMyKids
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Ground State Electronic Configuration of Selenium - neutral Selenium atom

Abbreviated electronic configuration of Selenium

The ground state abbreviated electronic configuration of Neutral Selenium atom is [Ar] 3d10 4s2 4p4. The portion of Selenium configuration that is equivalent to the noble gas of the preceding period, is abbreviated as [Ar]. For atoms with many electrons, this notation can become lengthy and so an abbreviated notation is used. This is important as it is the Valence electrons 4s2 4p4, electrons in the outermost shell that determine the chemical properties of the element.

Unabbreviated electronic configuration of neutral Selenium

Complete ground state electronic configuration for the Selenium atom, Unabbreviated electronic configuration

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4

Electrons are filled in atomic orbitals as per the order determined by the Aufbau principle, Pauli Exclusion Principle and Hund’s Rule.

  • As per the Aufbau principle the electrons will occupy the orbitals having lower energies before occupying higher energy orbitals. According to this principle, electrons are filled in the following order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p…
  • The Pauli exclusion principle states that a maximum of two electrons, each having opposite spins, can fit in an orbital.
  • Hund's rule states that every orbital in a given subshell is singly occupied by electrons before a second electron is filled in an orbital.
  • Electron configuration of Selenium
    Atomic Structure of Selenium

    Selenium atomic radius is 103 pm, while it's covalent radius is 116 pm.

    Atomic Radius Calculated

    103 pm (1.03 Å)

    Atomic Radius Empirical

    115 pm (1.15 Å)

    Atomic Volume16.385 cm3/mol
    Covalent Radius116 pm (1.16 Å)
    Van der Waals Radius190 pm
    Neutron Cross Section11.7
    Neutron Mass Absorption 0.0056

    Atomic Spectrum of Selenium

    Atomic Spectrum of Selenium | SchoolMyKids

    Selenium Chemical Properties: Selenium Ionization Energies and electron affinity

    The electron affinity of Selenium is 195 kJ/mol.

    Valence6
    Electronegativity2.55
    ElectronAffinity195 kJ/mol

    Ionization Energy of Selenium

    Refer to table below for Ionization energies of Selenium

    Ionization energy numberEnthalpy - kJ/mol
    1st941
    2nd2045
    3rd2973.7
    4th4144
    5th6590
    6th7880
    7th14990

    Selenium Physical Properties

    Refer to below table for Selenium Physical Properties

    Density4.819 g/cm3(when liquid at m.p density is $3.99 g/cm3)
    Molar Volume16.385 cm3/mol

    Elastic Properties

    Young Modulus10
    Shear Modulus3.7 GPa
    Bulk Modulus 8.3 GPa
    Poisson Ratio0.33

    Hardness of Selenium - Tests to Measure of Hardness of Element

    Mohs Hardness2 MPa
    Vickers Hardness-
    Brinell Hardness736 MPa

    Selenium Electrical Properties

    Selenium is Conductor of electricity. Refer to table below for the Electrical properties ofSelenium

    Electrical Conductivity-
    Resistivity-
    Superconducting Point-

    Selenium Heat and Conduction Properties

    Thermal Conductivity0.52 W/(m K)
    Thermal Expansion-

    Selenium Magnetic Properties

    Magnetic TypeDiamagnetic
    Curie Point-
    Mass Magnetic Susceptibility-4e-9 m3/kg
    Molar Magnetic Susceptibility-3.16e-10 m3/mol
    Volume Magnetic Susceptibility-0.0000193

    Optical Properties of Selenium

    Refractive Index1.000895

    Acoustic Properties of Selenium

    Speed of Sound3350 m/s

    Selenium Thermal Properties - Enthalpies and thermodynamics

    Refer to table below for Thermal properties of Selenium

    Melting Point494 K (220.85°C, 429.53000000000003 °F)
    Boiling Point958 K (684.85°C, 1264.73 °F)
    Critical Temperature1766 K
    Superconducting Point-

    Enthalpies of Selenium

    Heat of Fusion5.4 kJ/mol
    Heat of Vaporization26 kJ/mol
    Heat of Combustion-

    Selenium Isotopes - Nuclear Properties of Selenium

    Selenium has 30 isotopes, with between 65 and 94 nucleons. Selenium has 5 stable naturally occuring isotopes.

    Isotopes of Selenium - Naturally occurring stable Isotopes: 74Se, 76Se, 77Se, 78Se, 80Se.

    IsotopeZNIsotope Mass% AbundanceT halfDecay Mode
    65Se343165Synthetic
    66Se343266Synthetic
    67Se343367Synthetic
    68Se343468Synthetic
    69Se343569Synthetic
    70Se343670Synthetic
    71Se343771Synthetic
    72Se343872Synthetic
    73Se343973Synthetic
    74Se3440740.89%StableN/A
    75Se344175Synthetic
    76Se3442769.37%StableN/A
    77Se3443777.63%StableN/A
    78Se34447823.77%StableN/A
    79Se344579SyntheticStable
    80Se34468049.61%StableN/A
    81Se344781Synthetic
    82Se3448828.73%StableN/A
    83Se344983Synthetic
    84Se345084Synthetic
    85Se345185Synthetic
    86Se345286Synthetic
    87Se345387Synthetic
    88Se345488Synthetic
    89Se345589Synthetic
    90Se345690Synthetic
    91Se345791Synthetic
    92Se345892Synthetic
    93Se345993Synthetic
    94Se346094Synthetic

    Regulatory and Health - Health and Safety Parameters and Guidelines

    DOT Hazard Class{N/A, 6.1, N/A}
    DOT Numbers{N/A, 2658, N/A}
    EU Number-
    NFPA Fire Rating{N/A, 0, N/A}
    NFPA HazardsN/ A, N/ A, N/ A
    NFPA Health Rating{N/A, 2, N/A}
    NFPA Reactivity Rating{N/A, 0, N/A}
    Autoignition Point-
    Flashpoint-

    Database Search

    List of unique identifiers to search the element in various chemical registry databases

    DatabaseIdentifier number
    CAS Number - Chemical Abstracts Service (CAS)CAS7782-49-2
    RTECS Number{N/A, RTECSVS7700000, N/A}
    CID Number {CID6326970, CID6326970, CID139346}
    Gmelin Number-
    NSC Number-