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A simple example of a polyatomic ion is the hydroxide ion, which consists of one oxygen atom and one hydrogen atom, jointly carrying a net charge of −1; its chemical formula is O H −. In contrast, an ammonium ion consists of one nitrogen atom and four hydrogen atoms, with a charge of +1; its chemical formula is N H + 4.
Sodium nitrate has also been investigated as a phase-change material for thermal energy recovery, owing to its relatively high melting enthalpy of 178 J/g. [14] [15] Examples of the applications of sodium nitrate used for thermal energy storage include solar thermal power technologies and direct steam generating parabolic troughs. [14]
The driving force for this reaction is the reduction of electrical charge density on the anion and the elimination of the hydronium (H +) ion. The amount of order in the solution is decreased, releasing a certain amount of entropy which makes the Gibbs free energy more negative and favors the forward reaction.
Each ion can be either monatomic (termed simple ion), such as sodium (Na +) and chloride (Cl −) in sodium chloride, or polyatomic, such as ammonium (NH + 4) and carbonate (CO 2− 3) ions in ammonium carbonate. Salts containing basic ions hydroxide (OH −) or oxide (O 2−) are classified as bases, such as sodium hydroxide and potassium oxide.
Count valence electrons. Nitrogen has 5 valence electrons; each oxygen has 6, for a total of (6 × 2) + 5 = 17. The ion has a charge of −1, which indicates an extra electron, so the total number of electrons is 18. Connect the atoms by single bonds. Each oxygen must be bonded to the nitrogen, which uses four electrons—two in each bond.
Cations are positively (+) charged ions while anions are negatively (−) charged. This can be remembered with the help of the following mnemonics. Cats have paws ⇔ Cations are pawsitive. [27] Ca+ion: The letter t in cation looks like a + (plus) sign. [28] An anion is a negative ion. (An egative ion ⇒ Anion). [29]
The equilibrium, between the gas as a separate phase and the gas in solution, will by Le Châtelier's principle shift to favour the gas going into solution as the temperature is decreased (decreasing the temperature increases the solubility of a gas). When a saturated solution of a gas is heated, gas comes out of the solution.
The phosphotungstate anion, an example of a polyoxometalate. In chemistry, a polyoxometalate (abbreviated POM) is a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions linked together by shared oxygen atoms to form closed 3-dimensional frameworks.