O
octet
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A set of eight electrons in the valence shell of an atom.
olefin
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A hydrocarbon containing one or more double bonds between carbon atoms. Also called alkene.
optical isomer
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One of two or more compounds that have the same chemical composition and that have the same atoms joined to each other, but that oriented in space differently.
optically active
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Describing a substance having the ability to rotate the plane of polarized light passed through a solution of the substance.
orbital
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A mathematically defined region of electron density around one or more atoms.
ore
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Minerals from which metals are extracted.
organic
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In chemistry, organic refers to a species containing carbon. Certain small ions and compounds containing carbon (such as carbon dioxide) are usually not considered to be organic, but rather are classed as inorganic.
ortho
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Describing the relationship between two groups attached to carbon atoms on a benzene-like ring that have no carbon atoms between them.
osmosis
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The passage of solvent through a semipermeable membrane from a region of higher concentration of solute to a region of lower concentration of solute.
osmotic pressure
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The pressure required to prevent solvent from passing through a semipermeable membrane from a region of higher concentration of solute to a region of lower concentration of solute.
oxidation
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That part of a chemical reaction in which a reactant loses electrons; simultaneous reduction of a different reactant must occur.
oxidation number
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A formally defined charge that an atom in a compound or ion would have if the compound or ion existed entirely of monatomic ions.
oxidation state
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A formally defined charge that an atom in a compound or ion would have if the compound or ion existed entirely of monatomic ions.
oxidation-reduction reaction
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A reaction in which one reactant is oxidized (loses electrons) and one reactant is reduced (gains electrons), also called "redox reaction."
oxidizing agent
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A chemical species that accepts electrons in order to oxidize another species. In the process the oxidizing agent is itself reduced.
oxoacid
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An acid containing hydrogen, oxygen, and another element. Also called oxyacid.
oxoanion
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An anion containing oxygen and another element. Also called oxyanion.
oxyacid
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An acid containing hydrogen, oxygen, and another element. Also called oxoacid.
oxyanion
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An anion containing oxygen and another element. Also called oxoanion.
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