Definition of sigma in English:

sigma

Line breaks: sigma
Pronunciation: /ˈsɪɡmə
 
/

noun

1The eighteenth letter of the Greek alphabet (Σ, σ), transliterated as ‘s’.
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  • He coined this latter term and employed the Greek letter lower case sigma to denote its population parameter.
  • Alpha, rho, tau, sigma, omega, Ash went over the letters he saw in his mind while Lari just stared, apparently in her own little world.
  • Finally, even if epsilon is the correct reading, in the letter space to its right, where Meritt read part of an iota, are traces of what appears to be a sigma.
1.1 (Sigma) [followed by Latin genitive] Astronomy The eighteenth star in a constellation: Sigma Octantis
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  • Finally, the final green beam of light was shot straight up at the constellation Sigma.
1.2 Chemistry & Physics Relating to or denoting an electron or orbital with zero angular momentum about an internuclear axis: the σ orbital is localized symmetrically
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  • These conical intersections are fundamentally different from the ‘H-vinyl’ structures found in simple alkenes because they involve the interaction of four sigma electrons, as opposed to two pi electrons and two sigma electrons.
  • The sigma bond occupies the internuclear space, and the two pi bonds are at 90° angles to each other surrounding the carbon-carbon internuclear space.
  • The triple bond is composed of one sigma bond from overlap of sp hybrid orbitals, and two pi bonds, from overlap of two sets of p orbitals.

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Origin

Greek.

Definition of sigma in:

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