A period 2 element is one of the chemical elements in the second row (or "period") of the periodic table of the chemical elements. This second period contains more elements than period 1, with eight: 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 2s and 2p orbitals. Period 2 elements obey the octet rule in that they need eight electrons to complete their valence shell. The maximum number of electrons that these elements can accommodate is ten, two in the 1s orbital, two in the 2s orbital and six in the 2p orbital.
See also: Periodic table
Main article: Diatomic molecule
Main article: Lithium
Lithium (Li) is the chemical element with atomic number 3, occurring in two isotopes: 6Li and 7Li. At standard temperature and pressure, lithium is a soft, silver-white, highly reactive alkali metal. With a density of 0.564 gcm3, lithium is the lightest metal and the least dense solid element. The most common naturally occurring form of lithium is lithium-7, symbol 7Li, which comprises 92.5% of lithium abundance and has three protons and four neutrons. Lithium-6, symbol 6Li, is also stable, containing three protons and three neutrons. The two make up all natural occurrence of lithium on Earth, although further isotopes have been synthesised. In ionic compounds, lithium loses an electron to become positively charged, forming the cation Li+.
According to theory, Lithium is one of the few elements synthesised in the Big Bang, making it a primordial element. Lithium is the 33rd most abundant element on earth, occurring in concentrations of between 20 and 70 ppm by weight, but due to its high reactivity it is only ever found naturally in compounds. The most abundant source of lithium-containing compounds are granitic pegmatites, with spodumene and petalite being the most commercially-viable mineral sources for the element. Commercially, the metal is isolated electrolytically from a mixture of lithium chloride and potassium chloride.
Lithium salts are used in the pharmacology industry as mood stabilising drugs. 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. The most common compounds used are lithium carbonate, Li2CO3, lithium citrate, Li3C6H5O7, lithium sulphate, Li2SO4, and lithium orotate, LiC5H3N2O4H2O. 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.
Main article: Beryllium
Beryllium (Be) is the chemical element with atomic number 4, occurring in the form of 9Be. At standard temperature and pressure, beryllium is a strong, steel-grey, light-weight, brittle, bivalent alkali earth metal, with a density of 1.85 gcm3. It also has one of the highest melting points of all the light metals. Beryllium's most common isotope is 9Be, which contains 4 protons and 5 neutrons. It makes up almost 100% of all naturally occurring beryllium and is its only stable isotope; however other isotopes have been synthesised. In ionic compounds, beryllium loses its two valence electrons to form the cation, Be2+.
Small amounts of beryllium were synthesised during the Big Bang, although most of it decayed or reacted further to create larger nucleii, like carbon, nitrogen or oxygen. Beryllium is a component of 100 out of 4000 known minerals, such as bertrandite, Be4Si2O7(OH)2, beryl, Al2Be3Si6O18, chrysoberyl, Al2BeO4, and phenakite, Be2SiO4. Precious forms of beryl are aquamarine, bixbite and emerald. The most common sources of beryllium used commercially are beryl and bertrandite and production of it involves the reduction of beryllium fluoride with magnesium metal or the electrolysis of molten beryllium chloride, containing some sodium chloride as beryllium chloride is a poor conductor of electricity.
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. It is used as an alloying agent in beryllium copper, which is used to make electrical components due to its high electrical and heat conductivity. Sheets of beryllium are used in X-ray detectors to filter out visible light and let only X-rays through. It is used as a neutron moderator in nuclear reactors because light nuclei are more effective at slowing down neutrons than heavy nuclei. Beryllium's low weight and high rigidity also make it useful in the construction of tweeters in loudspeakers.
Beryllium and beryllium compounds are classified by the International Agency for Research on Cancer as Group 1 carcinogens; they are carcinogenic to both animals and humans. Chronic berylliosis is a pulmonary and systemic granulomatous disease caused by exposure to beryllium. Between 1% - 15% of people are sensitive to beryllium and may develop an inflammatory reaction in their respiratory system and skin, called chronic beryllium disease. 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. This can cause fever, fatigue, weakness, night sweats and difficulty in breathing.
Main article: Boron
Boron (B) is the chemical element with atomic number 5, occurring as 10B and 11B. At standard temperature and pressure, boron is a trivalent metalloid that has several different allotropes. Amorphous boron is a brown powder formed as a product of many chemical reactions. Crystalline boron is a very hard, black material with a high melting point and exists in many polymorphs: Two rhombohedral forms, -boron and -boron containing 12 and 106.7 atoms in the rhombohedral unit cell respectively, and 50-atom tetragonal boron are the most common. Boron has a density of 2.343. Boron's most common isotope is 11B at 80.22%, which contains 5 protons and 6 neutrons. The other common isotope is 10 at 19.78%, which contains 5 protons and 5 neutrons. These are the only stable isotopes of boron; however other isotopes have been synthesised. Boron forms covalent bonds with other nonmetals and has oxidation states of 1, 2, 3 and 4. Boron does not occur naturally as a free element, but in compounds such as borates. The most common sources of boron are tourmaline, borax, Na2B4O5(OH)48H2O, and kernite, Na2B4O5(OH)42H2O. it is diffucult to obtain pure boron. It can be made through the magnesium reduction of boron oxide, B2O3. This oxide is made by melting boric acid, B(OH)3, which in turn is obtained from borax. Small amounts of pure boron can be made by the thermal decomposition of boron bromide, BBr3, in hydrogen gas over hot tantalum wire, which acts as a catalyst. 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.
Boron is an essential plant micronutrient, required for cell wall strength and development, cell division, seed and fruit development, sugar transport and hormone development. However, high soil concentrations of over 1.0 ppm can cause necrosis in leaves and poor growth. Levels as low as 0.8 ppm can cause these symptoms to appear in plants particularly boron-sensitive. Most plants, even those tolerant of boron in the soil, will show symptoms of boron toxicity when boron levels are higher than 1.8 ppm. In animals, boron is an ultratrace element; in human diets, daily intake ranges from 2.14.3 mg boron/kg body weight (bw)/day. It is also used as a supplement for the prevention and treatment of osteoporosis and arthritis.
Main article: Carbon
Carbon is the chemical element with atomic number six, occurring as 12C, 13C and 14C. At standard temperature and pressure, carbon is a solid, occurring in many different allotropes, the most common of which are graphite, diamond, the fullerenes and amorphous carbon. 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. In contrast to the crystal lattice structure of diamond and graphite, the fullerenes are molecules, named after Richard Buckminster Fuller whose architecture the molecules resemble. There are several different fullerenes, the most widely known being the "buckeyball" C60. Little is known about the fullerenes and they are a current subject of research. There is also amorphous carbon, which is carbon without any crystalline structure. 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. Carbon's most common isotope at 98.9% is 12C, with six protons and six neutrons. 13C is also stable, with six protons and seven neutrons, at 1.1%. 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. Other isotopes of carbon have also been synthesised. Carbon forms covalent bonds with other non-metals with an oxidation state of -4, -2, +2 or +4.
Carbon is the fourth most abundant element in the universe by mass after hydrogen, helium and oxygen and is the second most abundant element in the human body by mass after oxygen, the third most abundant by number of atoms. There are an almost infinite number of compounds that contain carbon due to carbon's ability to form long stable chains of C C bonds. The simplest carbon-containing molecules are the hydrocarbons, which contain carbon and hydrogen, although they sometimes contain other elements in functional groups. Hydrocarbons are used as fossil fuels and to manufacture plastics and petrochemicals. All organic compounds, those essential for life, contain at least one atom of carbon. When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds including sugars, lignans, chitins, alcohols, fats, and aromatic esters, carotenoids and terpenes. With nitrogen it forms alkaloids, and with the addition of sulfur also it forms antibiotics, amino acids, and rubber products. 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.
Main article: Nitrogen
Nitrogen is the chemical element with atomic number seven, occurring as 13N, 14N and 15N. Under standard conditions, nitrogen is a colourless, odorless, tasteless non-metal. It is found mainly as mostly inert diatomic gas, N2, which makes up 78% of the earth's atmosphere.
Main article: Oxygen
Main article: Fluorine
Main article: Neon
Table of elements
Chemical elements in the second period
Element categories in the periodic table
Alkaline earth metals
Inner transition elements
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^ Nitrogen at WebElements.
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Standard Inline f-block Vertical Full names Names and atomic weights Text for last Large table Metals and nonmetals Blocks Valences Extension beyond the 7th period Electron configurations Atomic weights Electronegativities Alternatives Crystal structure
Lists of elements by
Name Atomic symbol Atomic number Atomic weight Name etymology (after places, after people) Discovery
Boiling point Melting point Density Oxidation state Abundance (in humans) Nuclear stability Hardness
1 (Alkali metals) 2 (Alkaline earth metals) 3 4 5 6 7 8 9 10 11 12 13 (Boron group) 14 (Carbon group) 15 (Pnictogens) 16 (Chalcogens) 17 (Halogens) 18 (Noble gases)
1 2 3 4 5 6 7 8
Other element categories
Metals Transition metals (1st row 2nd row 3rd row 4th row) Metalloids Nonmetals Lanthanides Actinides Rare earth elements Platinum group metals (PGMs) Post-transition metals
s-block p-block d-block f-block
Categories: Periodic table