so·di·um (s??d?-?m)n. Symbol Na A soft, light, extremely malleable silver-white element that is an alkali metal, reacts violently with water, is naturally abundant in combined forms, especially in common salt, and is used in the production of a wide variety of industrially important compounds. Sodium ions are essential to numerous biological processes in animals. Atomic number 11; atomic weight 22.9898; melting point 97.80°C; boiling point 883°C; specific gravity 0.971 (20°C); valence 1. See Periodic Table.[sod(a) + -ium.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.sodium (?s??d??m) n (Elements & Compounds) a. a very reactive soft silvery-white element of the alkali metal group occurring principally in common salt, Chile saltpetre, and cryolite. Sodium and potassium ions maintain the essential electrolytic balance in living cells. It is used in the production of chemicals, in metallurgy, and, alloyed with potassium, as a cooling medium in nuclear reactors. Symbol: Na; atomic no: 11; atomic wt: 22.989768; valency: 1; relative density: 0.971; melting pt: 97.81±0.03°C; boiling pt: 892.9°Cb. (as modifier): sodium light. [C19: New Latin, from soda + -ium]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014so?di?um (?so? di ?m) n. 1. a soft, silver-white, chemically active metallic element that occurs naturally only in combination: a necessary element in the body for the maintenance of normal fluid balance and other physiological functions. Symbol: Na; at. wt.: 22.9898; at. no.: 11; sp. gr.: 0.97 at 20°C. 2. any salt of sodium, as sodium chloride or sodium bicarbonate. [1807; sod (a) + -ium2] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.so·di·um (s??d?-?m) Symbol Na A soft, lightweight, silvery-white metallic element that reacts explosively with water. It is the most abundant alkali metal on Earth, occurring especially in common salt. Sodium is very easily shaped, and its compounds have many important uses in industry. Atomic number 11. See Periodic Table.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.