He - Helium
Helium Element Information, Facts, Properties, Trends, Uses, Comparison with other elements
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.
It belongs to group 18 of the periodic table having trivial name noble gases, aerogens. You can also download Printable Periodic Table of Elements Flashcards for Helium in a PDF format.
Helium Facts
Read key information and facts about element Helium
| Name | Helium |
| Atomic Number | 2 |
| Atomic Symbol | He |
| Atomic Weight | 4.002602 |
| Phase | Gas(Monoatomic Gas) |
| Color | Colorless |
| Appearance | colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field |
| Classification | Noble Gas |
| Natural Occurance | Primordial |
| Group in Periodic Table | 18 |
| Group Name | helium family or neon family |
| Period in Periodic Table | period 1 |
| Block in Periodic Table | p-block |
| Electronic Configuration | 1s2 |
| Electronic Shell Structure (Electrons per shell) | 2 |
| Melting Point | 0 K |
| Boiling Point | 4.22 K |
| CAS Number | CAS7440-59-7 |
How to Locate Helium 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 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.
Helium History
The element Helium was discovered by P. Janssen and N. Lockyer in year 1868 in Sweden and United Kingdom. Helium was first isolated by W. Ramsay,T. Cleve, and N. Langlet in 1895. Helium derived its name from the Greek word helios, meaning 'sun'.
| Discovered By | P. Janssen and N. Lockyer |
| Discovery Date | 1868 in Sweden and United Kingdom |
| First Isolation | 1895 |
| Isolated by | W. Ramsay,T. Cleve, and N. Langlet |
Janssen and Lockyer observed independently a yellow line in the solar spectrum that did not match any other element. Years later, Ramsay, Cleve, and Langlet observed independently the element trapped in cleveite about the same time.
Helium Uses
Helium gas is usually identified to be lighter than air, which leads to its use in weather and party balloons. It is also used as an inert shield for arc welding and to pressurize liquid fuel tanks in rockets.
Helium Presence: Abundance in Nature and Around Us
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 %) | ppb by atoms (1ppb =10^-7 %) | |
|---|---|---|
| Abundance in Universe | 230000000 | 72000000 |
| Abundance in Sun | 230000000 | 74000000 |
| Abundance in Meteorites | - | - |
| Abundance in Earth's Crust | 5.5 | 30 |
| Abundance in Oceans | 0.0072 | 0.011 |
| Abundance in Humans | - | - |
Crystal Structure of Helium
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.
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)
| a | b | c |
|---|---|---|
| 424.2 pm | 424.2 pm | 424.2 pm |
and the angles between them Lattice Angles (alpha, beta and gamma).
| alpha | beta | gamma |
|---|---|---|
| π/2 | π/2 | 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 Name | Fm_ 3m |
| Space Group Number | 225 |
| Crystal Structure | Face Centered Cubic |
| Number of atoms per unit cell | 4 |
The number of atoms per unit cell in a simple cubic, face-centered cubic and body-centred cubic are 1,4,2 respectively.
Helium Atomic and Orbital Properties
Helium atoms have 2 electrons and the electronic shell structure is [2] with Atomic Term Symbol (Quantum Numbers) 1S0.
| Atomic Number | 2 |
| Number of Electrons (with no charge) | 2 |
| Number of Protons | 2 |
| Mass Number | 4 |
| Number of Neutrons | 2 |
| Shell structure (Electrons per energy level) | 2 |
| Electron Configuration | 1s2 |
| Valence Electrons | 1s2 |
| Valence (Valency) | 0 |
| Main Oxidation States | - |
| Oxidation States | |
| Atomic Term Symbol (Quantum Numbers) | 1S0 |
Bohr Atomic Model of Helium - Electrons per energy level
| n | s | p | d | f |
|---|
Ground State Electronic Configuration of Helium - neutral Helium atom
Abbreviated electronic configuration of Helium
The ground state abbreviated 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 . 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.
Unabbreviated electronic configuration of neutral Helium
Complete ground state electronic configuration for the Helium atom, Unabbreviated electronic configuration
1s2
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.
Atomic Structure of Helium
Helium atomic radius is 31 pm, while it's covalent radius is 32 pm.
| Atomic Radius Calculated | 31 pm(0.31 Å) |
| Atomic Radius Empirical | 120 pm (1.2 Å) |
| Atomic Volume | 22.4136 cm3/mol |
| Covalent Radius | 32 pm (0.32 Å) |
| Van der Waals Radius | 140 pm |
| Neutron Cross Section | 0.007 |
| Neutron Mass Absorption | 0.00001 |
Spectral Lines of Helium - Atomic Spectrum of Helium
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identify atoms and molecules.
Spectral lines are the result of interaction between a quantum system and a single photon. A spectral line may be observed either as an emission line or an absorption line.
Spectral lines are highly atom-specific, and can be used to identify the chemical composition of any medium. Several elements, including helium, thallium, and caesium, were discovered by spectroscopic means. They are widely used to determine the physical conditions of stars and other celestial bodies that cannot be analyzed by other means.
Emission spectrum of Helium
Absorption spectrum of Helium
Helium Chemical Properties: Helium Ionization Energies and electron affinity
The electron affinity of Helium is 0 kJ/mol.
| Valence | 0 |
| Electronegativity | - |
| ElectronAffinity | 0 kJ/mol |
Ionization Energy of Helium
Ionization energy is the amount of energy required to remove an electron from an atom or molecule.in chemistry, this energy is expresed in kilocalories per mole (kcal/mol) or kilojoules per mole (kJ/mol).
Refer to table below for Ionization energies of Helium
| Ionization energy number | Enthalpy - kJ/mol |
|---|---|
| 1st | 2372.3 |
| 2nd | 5250.5 |
Helium Physical Properties
Refer to below table for Helium Physical Properties
| Density | 0.0001785 g/cm3 |
| Molar Volume | 22.4136 cm3/mol |
Elastic Properties
| Young Modulus | - |
| Shear Modulus | - |
| Bulk Modulus | - |
| Poisson Ratio | - |
Hardness of Helium - Tests to Measure of Hardness of Element
| Mohs Hardness | - |
| Vickers Hardness | - |
| Brinell Hardness | - |
Helium Electrical Properties
Electrical resistivity measures element's electrical resistance or how strongly it resists electric current.The SI unit of electrical resistivity is the ohm-metre (Ω⋅m). While Electrical conductivity is the reciprocal of electrical resistivity. It represents a element's ability to conduct electric current. The SI unit of electrical conductivity is siemens per metre (S/m).
Helium is a -. Refer to table below for the Electrical properties of Helium
| Electrical conductors | - |
| Electrical Conductivity | - |
| Resistivity | - |
| Superconducting Point | - |
Helium Heat and Conduction Properties
| Thermal Conductivity | 0.1513 W/(m K) |
| Thermal Expansion | - |
Helium Magnetic Properties
| Magnetic Type | Diamagnetic |
| Curie Point | - |
| Mass Magnetic Susceptibility | -5.9e-9 m3/kg |
| Molar Magnetic Susceptibility | -2.36e-11 m3/mol |
| Volume Magnetic Susceptibility | -1.05e-9 |
Optical Properties of Helium
| Refractive Index | 1.000035 |
Acoustic Properties of Helium
| Speed of Sound | 970 m/s |
Helium Thermal Properties - Enthalpies and thermodynamics
Refer to table below for Thermal properties of Helium
| Melting Point | 0 K0 |
| Boiling Point | 4.22 K(-268.93 °C, -452.074 °F) |
| Critical Temperature | 5.19 K |
| Superconducting Point | - |
Enthalpies of Helium
| Heat of Fusion | 0.02 kJ/mol |
| Heat of Vaporization | 0.083 kJ/mol |
| Heat of Combustion | - |
Helium Isotopes - Nuclear Properties of Helium
Helium has 8 isotopes, with between 3 and 10 nucleons. Helium has 2 stable naturally occuring isotopes.
Isotopes of Helium - Naturally occurring stable Isotopes: 3He, 4He.
| Isotope | Z | N | Isotope Mass | % Abundance | T half | Decay Mode |
|---|---|---|---|---|---|---|
| 3He | 2 | 1 | 3 | 0.000137% | Stable | N/A |
| 4He | 2 | 2 | 4 | 99.999863% | Stable | |
| 5He | 2 | 3 | 5 | Synthetic | ||
| 6He | 2 | 4 | 6 | Synthetic | ||
| 7He | 2 | 5 | 7 | Synthetic | ||
| 8He | 2 | 6 | 8 | Synthetic | ||
| 9He | 2 | 7 | 9 | Synthetic | ||
| 10He | 2 | 8 | 10 | Synthetic |
Regulatory and Health - Health and Safety Parameters and Guidelines
The United States Department of Transportation (DOT) identifies hazard class of all dangerous elements/goods/commodities either by its class (or division) number or name. The DOT has divided these materials into nine different categories, known as Hazard Classes.
| DOT Numbers | 1963 |
| DOT Hazard Class | 2.2 |
NFPA 704 is a Standard System for the Identification of the Hazards of Materials for Emergency Response. NFPA is a standard maintained by the US based National Fire Protection Association.
The health (blue), flammability (red), and reactivity (yellow) rating all use a numbering scale ranging from 0 to 4. A value of zero means that the element poses no hazard; a rating of four indicates extreme danger.
| NFPA Fire Rating | 0 | Will not burn |
| NFPA Health Rating | 1 | Flash Points Above 93.3°C (200°F) |
| NFPA Reactivity Rating | 0 | Will not burn |
| NFPA Hazards |
| Autoignition Point | - |
| Flashpoint | - |
Database Search
List of unique identifiers to search the element in various chemical registry databases
| Database | Identifier number |
|---|---|
| CAS Number - Chemical Abstracts Service (CAS) | CAS7440-59-7 |
| RTECS Number | RTECSMH6520000 |
| CID Number | CID23987 |
| Gmelin Number | - |
| NSC Number | - |
Compare Helium with other elements
Compare Helium with Group 18, Period 1 and Noble Gas elements of the periodic table.
Compare Helium with all Group 18 elements
Compare Helium with all Period 1 elements
Compare Helium with all Noble Gas elements
Frequently Asked Questions (FAQ)
Find the answers to the most frequently asked questions about Helium