Period 2 element
The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases; a new row is started when chemical behavior begins to repeat, creating columns of elements with similar properties.
The second period contains the elements lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon.
In a quantum mechanical description of atomic structure, this period corresponds to the filling of the second (n = 2) shell, more specifically its 2s and 2p subshells.
[note 2] At standard temperature and pressure, lithium is a soft, silver-white, highly reactive metal.
Lithium is the 31st most abundant element on earth,[7] occurring in concentrations of between 20 and 70 ppm by weight,[8] but due to its high reactivity it is only found naturally in compounds.
[9][10] They are used in the treatment of bipolar disorder, where they have a role in treating depression and mania and may reduce the chances of suicide.
Lithium is also used in batteries as an anode and its alloys with aluminium, cadmium, copper and manganese are used to make high performance parts for aircraft, most notably the external tank of the Space Shuttle.
At standard temperature and pressure, beryllium is a strong, steel-grey, light-weight, brittle, bivalent alkaline earth metal, with a density of 1.85 g⋅cm−3.
Small amounts of beryllium were synthesised during the Big Bang, although most of it decayed or reacted further to create larger nuclei, like carbon, nitrogen or oxygen.
[12] Due to its stiffness, light weight, and dimensional stability over a wide temperature range, beryllium metal is used in as a structural material in aircraft, missiles and communication satellites.
The body's immune system recognises the beryllium as foreign particles and mounts an attack against them, usually in the lungs where they are breathed in.
[17] The most commercially important sources of boron are: sodium tetraborate pentahydrate, Na2B4O7 · 5H2O, which is used in large amounts in making insulating fiberglass and sodium perborate bleach; boron carbide, a ceramic material, is used to make armour materials, especially in bulletproof vests for soldiers and police officers; orthoboric acid, H3BO3 or boric acid, used in the production of textile fiberglass and flat panel displays; sodium tetraborate decahydrate, Na2B4O7 · 10H2O or borax, used in the production of adhesives; and the isotope boron-10 is used as a control for nuclear reactors, as a shield for nuclear radiation, and in instruments used for detecting neutrons.
[18] In animals, boron is an ultratrace element; in human diets, daily intake ranges from 2.1 to 4.3 mg boron/kg body weight (bw)/day.
[25] Graphite is a soft, hexagonal crystalline, opaque black semimetal with very good conductive and thermodynamically stable properties.
Diamond however is a highly transparent colourless cubic crystal with poor conductive properties, is the hardest known naturally occurring mineral and has the highest refractive index of all gemstones.
[26] In mineralogy, the term is used to refer to soot and coal, although these are not truly amorphous as they contain small amounts of graphite or diamond.
[29] Trace amounts of 14C also occur naturally but this isotope is radioactive and decays with a half life of 5730 years; it is used for radiocarbon dating.
[34][35] When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds[35] including sugars, lignans, chitins, alcohols, fats, and aromatic esters, carotenoids and terpenes.
With the addition of phosphorus to these other elements, it forms DNA and RNA, the chemical-code carriers of life, and adenosine triphosphate (ATP), the most important energy-transfer molecule in all living cells.
The element nitrogen was discovered as a separable component of air, by Scottish physician Daniel Rutherford, in 1772.
[37] Many industrially important compounds, such as ammonia, nitric acid, organic nitrates (propellants and explosives), and cyanides, contain nitrogen.
It resides in the chemical structure of almost all neurotransmitters, and is a defining component of alkaloids, biological molecules produced by many organisms.
Oxygen is part of substances best described as some salts of metals and oxygen-containing acids (thus nitrates, sulfates, phosphates, silicates, and carbonates.
Animals especially but also fungi and bacteria ultimately depend upon photosynthesizing plants and phytoplankton for food and oxygen.
Fire uses oxygen to oxidize compounds typically of carbon and hydrogen to water and carbon dioxide (although other elements may be involved) whether in uncontrolled conflagrations that destroy buildings and forests or the controlled fire within engines or that supply electrical energy from turbines, heat for keeping buildings warm, or the motive force that drives vehicles.
Unlike regular diatomic oxygen, ozone is a toxic material generally considered a pollutant.
Fluorine even attacks silica, one of the favored materials for transporting strong acids, and burns asbestos.
Fluorine gas is extremely dangerous because it attacks almost all organic material, including live flesh.
With sulfur it can form the extremely stable and chemically inert sulfur hexafluoride; with carbon it can form the remarkable material Teflon that is a stable and non-combustible solid with a high melting point and a very low coefficient of friction that makes it an excellent liner for cooking pans and raincoats.
