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Ions consisting of only a single atom are termed atomic or monatomic ions, while two or more atoms form molecular ions or polyatomic ions. In the case of physical ionization in a fluid (gas or liquid), "ion pairs" are created by spontaneous molecule collisions, where each generated pair consists of a free electron and a positive ion. [5]
The name of the cation (the unmodified element name for monatomic cations) comes first, followed by the name of the anion. [100] [101] For example, MgCl 2 is named magnesium chloride, and Na 2 SO 4 is named sodium sulfate (SO 2− 4, sulfate, is an example of a polyatomic ion).
For example, each molecule of oxygen (O 2) is composed of two oxygen atoms. Therefore, the atomicity of oxygen is 2. [1] In older contexts, atomicity is sometimes equivalent to valency. Some authors also use the term to refer to the maximum number of valencies observed for an element. [2]
It is usually applied to gases: a monatomic gas is a gas in which atoms are not bound to each other. Examples at standard conditions of temperature and pressure include all the noble gases ( helium , neon , argon , krypton , xenon , and radon ), though all chemical elements will be monatomic in the gas phase at sufficiently high temperature (or ...
The lethal dose for most adult humans is estimated at 5 to 10 g (which is equivalent to 32 to 64 mg elemental fluoride per kg body weight). [ 53 ] [ 54 ] [ 55 ] A case of a fatal poisoning of an adult with 4 grams of sodium fluoride is documented, [ 56 ] and a dose of 120 g sodium fluoride has been survived. [ 57 ]
Examples of mesons include the pion, kaon, and the J/ψ. In quantum hadrodynamics, mesons mediate the residual strong force between nucleons. At one time or another, positive signatures have been reported for all of the following exotic mesons but their existences have yet to be confirmed.
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]
A test for the presence of iodide ions is the formation of yellow precipitates of these compounds upon treatment of a solution of silver nitrate or lead(II) nitrate. [2] Aqueous solutions of iodide salts dissolve iodine better than pure water. This effect is due to the formation of the triiodide ion, which is brown: I − + I 2 ⇌ I − 3