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n. Symbol Se
A nonmetallic element, red in powder form, black in vitreous form, and metallic gray in stable crystalline form, resembling sulfur and found as an impurity in pyrites or obtained as a byproduct of electrolytic copper refining. It is widely used in rectifiers, as a semiconductor, and in xerography. Its photovoltaic and photoconductive actions make it useful in photocells, photographic exposure meters, and solar cells. Atomic number 34; atomic weight 78.96; melting point (gray) 221°C; boiling point (gray) 685°C; specific gravity (gray) 4.79; (vitreous) 4.28; valence 2, 4, or 6. See Periodic Table.
[Greek selēnē, moon (from selas, light, brightness) + -ium.]
(Elements & Compounds) a nonmetallic element that exists in several allotropic forms. It occurs free in volcanic areas and in sulphide ores, esp pyrite. The common form is a grey crystalline solid that is photoconductive, photovoltaic, and semiconducting: used in photocells, solar cells, and in xerography. Symbol: Se; atomic no: 34; atomic wt: 78.96; valency: –2, 4, or 6; relative density: 4.79 (grey); melting pt: 221°C (grey); boiling pt: 685°C (grey)
[C19: from New Latin, from Greek selēnē moon; named by analogy to tellurium (from Latin tellus earth)]
se•le•ni•um(sɪˈli ni əm)
a nonmetallic element occurring in several allotropic forms and having an electrical resistance that varies under the influence of light. Symbol: Se; at. wt.: 78.96; at. no.: 34; sp. gr.: (gray) 4.80 at 25°C, (red) 4.50 at 25°C.
[< New Latin (1818) < Greek selḗn(ē) moon + New Latin -ium -ium2]
Symbol Se A nonmetallic element that can exist as a gray crystal, a red powder, or a black glassy material. It can convert light directly into electricity, and its ability to conduct electricity increases as light striking it becomes more intense. Because of this, selenium is used in copy machines, photography, and solar cells. Atomic number 34. See Periodic Table.
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|Noun||1.||selenium - a toxic nonmetallic element related to sulfur and tellurium; occurs in several allotropic forms; a stable grey metallike allotrope conducts electricity better in the light than in the dark and is used in photocells; occurs in sulfide ores (as pyrite)|
chemical element, element - any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter
antioxidant - substance that inhibits oxidation or inhibits reactions promoted by oxygen or peroxides