Period 1 element
The periodic table is laid out in rows to illustrate periodic (recurring) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that analog elements fall into the same vertical columns.
In a quantum mechanical description of atomic structure, this period corresponds to the filling of the 1s orbital.
Period 1 elements obey the duet rule in that they need two electrons to complete their valence shell.
The valence shell lacks "p" or any other kind of orbitals due to the general l < n constraint on the quantum numbers.
[6] Hydrogen thus has properties corresponding to both those of the alkali metals and the halogens, but matches neither group perfectly, and is thus difficult to place by its chemistry.
At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H2.
Elemental hydrogen is relatively rare on Earth, and is industrially produced from hydrocarbons such as methane, after which most elemental hydrogen is used "captively" (meaning locally at the production site), with the largest markets almost equally divided between fossil fuel upgrading, such as hydrocracking, and ammonia production, mostly for the fertilizer market.
[24] It plays a particularly important role in acid-base chemistry, in which many reactions involve the exchange of protons between soluble molecules.
[31] Helium (He) is a colorless, odorless, tasteless, non-toxic, inert monatomic chemical element that heads the noble gas series in the periodic table and whose atomic number is 2.
[32] Its boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions.
[33] Helium was discovered in 1868 by French astronomer Pierre Janssen, who first detected the substance as an unknown yellow spectral line signature in light from a solar eclipse.
[35] The substance is used in cryogenics,[36] in deep-sea breathing systems,[37] to cool superconducting magnets, in helium dating,[38] for inflating balloons,[39] for providing lift in airships,[40] and as a protective gas for industrial uses such as arc welding and growing silicon wafers.
This radiogenic helium is trapped with natural gas in concentrations of up to seven percent by volume,[48] from which it is extracted commercially by a low-temperature separation process called fractional distillation.
