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Period 1 element


Period 1 element

Period 1 in the periodic table

A period 1 element is one of the chemical elements in the first row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) 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 elements with similar behaviour fall into the same vertical columns. The first period contains fewer elements than any other row in the table, with only two: hydrogen and helium. This situation can be explained by modern theories of atomic structure. 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 maximum number of electrons that these elements can accommodate is two, both in the 1s orbital. Therefore, period 1 can have only two elements.


  • Periodic trends 1
  • Position of period 1 elements in the periodic table 2
  • Elements 3
    • Hydrogen 3.1
    • Helium 3.2
  • References 4
  • Further reading 5

Periodic trends

All other periods in the period table contain at least 8 elements, and it is often helpful to consider periodic trends across the period. However, period 1 contains only two elements, so this concept does not apply here.

In terms of vertical trends down groups, helium can be seen as a typical noble gas at the head of Group 18, but as discussed below, hydrogren's chemistry is unique and it is not easily assigned to any group.

Position of period 1 elements in the periodic table

Although both hydrogen and helium are in the s-block, neither of them behaves similarly to other s-block elements. Their behaviour is so different from the other s-block elements that there is considerable disagreement over where these two elements should be placed in the periodic table.

Hydrogen is sometimes placed above lithium,[1] above carbon,[2] above fluorine,[2][3] above both lithium and fluorine (appearing twice),[4] or left floating above the other elements and not assigned to any group[4] in the periodic table.

Helium is almost always placed above neon (which is in the p-block) in the periodic table as a noble gas,[1] although it is occasionally placed above beryllium due to their similar electron configuration.[5]


Chemical element Chemical series Electron configuration
1 H Hydrogen Diatomic nonmetal 1s1
2 He Helium Noble gas 1s2


Hydrogen discharge tube
Deuterium discharge tube

Hydrogen (H) is the chemical element with atomic number 1. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H2. With an atomic mass of 1.00794 amu, hydrogen is the lightest element.[6]

Hydrogen is the most abundant of the chemical elements, constituting roughly 75% of the universe's elemental mass.[7] Stars in the main sequence are mainly composed of hydrogen in its plasma state. 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. Hydrogen may be produced from water using the process of electrolysis, but this process is significantly more expensive commercially than hydrogen production from natural gas.[8]

The most common naturally occurring

  • Bloch, D. R. (2006). Organic Chemistry Demystified. McGraw-Hill Professional.  

Further reading

  1. ^ a b "International Union of Pure and Applied Chemistry > Periodic Table of the Elements". IUPAC. Retrieved 2011-05-01. 
  2. ^ a b Cronyn, Marshall W. (August 2003). "The Proper Place for Hydrogen in the Periodic Table". Journal of Chemical Education 80 (8): 947–951.  
  3. ^ Vinson, Greg (2008). "Hydrogen is a Halogen". Retrieved January 14, 2012. 
  4. ^ a b Kaesz, Herb; Atkins, Peter (November–December 2003). "A Central Position for Hydrogen in the Periodic Table". Chemistry International ( 
  5. ^ Winter, Mark (1993–2011). "Janet periodic table". WebElements. Retrieved January 19, 2012. 
  6. ^ "Hydrogen – Energy". Energy Information Administration. Retrieved 2008-07-15. 
  7. ^ Palmer, David (November 13, 1997). "Hydrogen in the Universe". NASA. Retrieved 2008-02-05. 
  8. ^ Staff (2007). "Hydrogen Basics — Production". Florida Solar Energy Center. Retrieved 2008-02-05. 
  9. ^ Sullivan, Walter (1971-03-11). "Fusion Power Is Still Facing Formidable Difficulties". The New York Times. 
  10. ^ "hydrogen".  
  11. ^ Eustis, S. N.; Radisic, D; Bowen, KH; Bachorz, RA; Haranczyk, M; Schenter, GK; Gutowski, M (2008-02-15). "Electron-Driven Acid-Base Chemistry: Proton Transfer from Hydrogen Chloride to Ammonia". Science 319 (5865): 936–939.  
  12. ^ "Time-dependent Schrödinger equation".  
  13. ^ Rogers, H. C. (1999). "Hydrogen Embrittlement of Metals". Science 159 (3819): 1057–1064.  
  14. ^ Christensen, C. H.; Nørskov, J. K.; Johannessen, T. (July 9, 2005). "Making society independent of fossil fuels — Danish researchers reveal new technology". Technical University of Denmark. Retrieved 2008-03-28. 
  15. ^ Takeshita, T.; Wallace, W.E.; Craig, R.S. (1974). "Hydrogen solubility in 1:5 compounds between yttrium or thorium and nickel or cobalt". Inorganic Chemistry 13 (9): 2282–2283.  
  16. ^ Kirchheim, R.; Mutschele, T.; Kieninger, W (1988). "Hydrogen in amorphous and nanocrystalline metals". Materials Science and Engineering 99: 457–462.  
  17. ^ Kirchheim, R. (1988). "Hydrogen solubility and diffusivity in defective and amorphous metals". Progress in Materials Science 32 (4): 262–325.  
  18. ^ "Helium: the essentials". WebElements. Retrieved 2008-07-15. 
  19. ^ "Helium: physical properties". WebElements. Retrieved 2008-07-15. 
  20. ^ "Pierre Janssen". MSN Encarta. Retrieved 2008-07-15. 
  21. ^ Theiss, Leslie (2007-01-18). "Where Has All the Helium Gone?". Bureau of Land Management. Retrieved 2008-07-15. 
  22. ^ Timmerhaus, Klaus D. (2006-10-06). Cryogenic Engineering: Fifty Years of Progress. Springer.  
  23. ^ Copel, M. (September 1966). "Helium voice unscrambling". Audio and Electroacoustics 14 (3): 122–126.  
  24. ^ "helium dating".  
  25. ^ Brain, Marshall. "How Helium Balloons Work". How Stuff Works. Retrieved 2008-07-15. 
  26. ^ Jiwatram, Jaya (2008-07-10). "The Return of the Blimp". Popular Science. Retrieved 2008-07-15. 
  27. ^ "When good GTAW arcs drift; drafty conditions are bad for welders and their GTAW arcs.". Welding Design & Fabrication. 2005-02-01. 
  28. ^ Montgomery, Craig (2006-09-04). "Why does inhaling helium make one's voice sound strange?". Scientific American. Retrieved 2008-07-15. 
  29. ^ "Probable Discovery Of A New, Supersolid, Phase Of Matter". Science Daily. 2004-09-03. Retrieved 2008-07-15. 
  30. ^ Browne, Malcolm W. (1979-08-21). "Scientists See Peril In Wasting Helium; Scientists See Peril in Waste of Helium". The New York Times. 
  31. ^ "Helium: geological information". WebElements. Retrieved 2008-07-15. 
  32. ^ Cox, Tony (1990-02-03). "Origin of the chemical elements". New Scientist. Retrieved 2008-07-15. 
  33. ^ "Helium supply deflated: production shortages mean some industries and partygoers must squeak by.". Houston Chronicle. 2006-11-05. 
  34. ^ Brown, David (2008-02-02). "Helium a New Target in New Mexico". American Association of Petroleum Geologists. Retrieved 2008-07-15. 
  35. ^ Voth, Greg (2006-12-01). "Where Do We Get the Helium We Use?". The Science Teacher. 


Helium is the second lightest element and is the second most abundant in the observable universe.[31] Most helium was formed during the Big Bang, but new helium is being created as a result of the nuclear fusion of hydrogen in stars.[32] On Earth, helium is relatively rare and is created by the natural decay of some radioactive elements[33] because the alpha particles that are emitted consist of helium nuclei. This radiogenic helium is trapped with natural gas in concentrations of up to seven percent by volume,[34] from which it is extracted commercially by a low-temperature separation process called fractional distillation.[35]

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.[20] In 1903, large reserves of helium were found in the natural gas fields of the United States, which is by far the largest supplier of the gas.[21] The substance is used in cryogenics,[22] in deep-sea breathing systems,[23] to cool superconducting magnets, in helium dating,[24] for inflating balloons,[25] for providing lift in airships,[26] and as a protective gas for industrial uses such as arc welding and growing silicon wafers.[27] Inhaling a small volume of the gas temporarily changes the timbre and quality of the human voice.[28] The behavior of liquid helium-4's two fluid phases, helium I and helium II, is important to researchers studying quantum mechanics and the phenomenon of superfluidity in particular,[29] and to those looking at the effects that temperatures near absolute zero have on matter, such as with superconductivity.[30]

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.[18] Its boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions.[19]

Helium discharge tube


The interactions of hydrogen with various metals are very important in metallurgy, as many metals can suffer hydrogen embrittlement,[13] and in developing safe ways to store it for use as a fuel.[14] Hydrogen is highly soluble in many compounds composed of rare earth metals and transition metals[15] and can be dissolved in both crystalline and amorphous metals.[16] Hydrogen solubility in metals is influenced by local distortions or impurities in the metal crystal lattice.[17]

[12].quantum mechanics of the hydrogen atom has played a key role in the development of spectrum can be solved analytically, study of the energetics and Schrödinger equation As the only neutral atom for which the [11], in which many reactions involve the exchange of protons between soluble molecules.acid-base chemistry It plays a particularly important role in [10]

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