Helium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among all the elements.
Read key information and facts about element Helium
|Group in Periodic Table||18|
|Group Name||helium family or neon family|
|Period in Periodic Table||1|
|Block in Periodic Table||p-block|
|Boiling Point||-268.93 °C|
|Electronic Shell Structure|||
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 2 to find Helium 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 Helium on periodic table look for cross section of group 18 and period 1 in the modern periodic table.
The element Helium was discovered by Pierre Janssen in year 1895 in Sweden and United Kingdom . Helium derived its name from the Greek word helios, meaning 'sun'
The table below shows the abundance of Helium in Universe, Sun, Meteorites, Earth's Crust, Oceans and Human Body.
|Ppb by weight (1ppb =10^-7 %)|
|Abundance in Universe||0.23|
|Abundance in Sun||0.23|
|Abundance in Meteorites||N/A|
|Abundance in Earth's Crust||5.5×10-7%|
|Abundance in Oceans||7.2×10-10%|
|Abundance in Humans||N/A|
The solid state structure of Helium is Face Centered Cubic.
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.
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)
and the angles between them Lattice Angles (alpha, beta and gamma).
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 Name||Fm_ 3m|
|Space Group Number||225|
|Crystal Structure||Face Centered Cubic|
Helium atoms have 2 electrons and the electronic shell structure is  with Atomic Term Symbol (Quantum Numbers) 1S0.
|Number of Electrons (with no charge)||2|
|Number of Protons||2|
|Number of Neutrons||2|
|Shell structure (Electrons per energy level)|||
|Atomic Term Symbol (Quantum Numbers)||1S0|
Shell Structure of Helium - Electrons per energy level
The ground state electronic configuration of Neutral Helium atom is 1s2. The portion of Helium configuration that is equivalent to the noble gas of the preceding period, is abbreviated as 1s2]. 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 1s2, electrons in the outermost shell that determine the chemical properties of the element.
Complete ground state electronic configuration for the Helium atom, Unabbreviated electronic configuration
Helium atomic radius is 31 pm, while it's covalent radius is 32 pm.
31 pm (0.31 Å)
|Atomic Volume||22.4235406162 cm3|
|Covalent Radius||32 pm (0.32 Å)|
|Van der Waals Radius||140 pm|
|Neutron Cross Section||0.007 σa/barns|
The electron affinity of Helium is 0 kJ/mol
Refer to table below for Ionization energies of Helium
|Ionization energy number||Enthalpy - kJ/mol|
Refer to below table for Helium Physical Properties
|Molar Volume||22.4235406162 cm3|
Helium is N/A of electricity. Refer to table below for the Electrical properties of Helium
|Thermal Conductivity||0.1513 W/(m K)|
|Mass Magnetic Susceptibility||-5.9×10-9|
|Molar Magnetic Susceptibility||-2.36×10-11|
|Volume Magnetic Susceptibility||-1.05×10-9|
|Speed of Sound||970 m/s|
Refer to table below for Thermal properties of Helium
|Melting Point||N/A (N/A)|
|Boiling Point||4.22 K (-268.93 °C)|
|Critical Temperature||5.19 K|
|Heat of Fusion||0.02 kJ/mol|
|Heat of Vaporization||0.083 kJ/mol|
|Heat of Combustion||N/A|
Isotopes of rhodium. Naturally occurring Helium has 2 stable isotope - 3He, 4He.
|Isotope||Isotope Mass||% Abundance||T half||Decay Mode|
|DOT Hazard Class||2.2|
|NFPA Fire Rating||0|
|NFPA Health Rating||1|
|NFPA Reactivity Rating||0|
List of unique identifiers to search the element in various chemical registry databases
|CAS Number - Chemical Abstracts Service (CAS)||CAS7440-59-7|
|Alkali Metals||Alkaline Earth Metals|
|Transition Metals||Post-Transition Metals|