Hydration - Suiwa

Generally, it refers to a chemical species (ion, inorganic compound, organic compound, etc.) bonding with water. [ I ] Charged particles (ions, electrons) dissolved in water strongly attract one or more water molecules around them, and as a whole they exhibit a single collective property. In the case of ions, they are called hydrated ions, and in the case of electrons, they are called hydrated electrons. Hydration releases hydration energy. The interaction between the particle and the water molecule is due to the electrostatic attraction between the charge and the dipole of the water molecule. When a hydrated ion or hydrated electron moves due to the action of an electric field, the charged particle moves with the hydrated water molecule, so the mobility depends on the degree of hydration. For example, the conductivity of ions in an aqueous solution is Li ⁺ < Na ⁺ < K ⁺ , which is the opposite order to that expected from the size of the ion itself. This is because the smaller the ion, such as Li ⁺ , the smaller the effective distance between the charge and the dipole, and therefore the greater the degree of hydration. When low-pressure gas X is bombarded with electrons in the presence of water vapor, it has been found by mass spectrometry that higher ions such as X ⁺ (H ₂ O) _n ( n is an integer) can be produced by ion-molecule reactions; these are also called hydrated ions. [ II ] If the unshared electron pair of a water molecule is donated to the vacant orbital of an ion, it essentially becomes a covalent bond, for example, [Co(H ₂ O) ₆ ] ²⁺ can be produced. This is also called hydration. Aquation is one example of this. [ III ] An anhydride takes in water of crystallization. [See alternative terminology] Hydrate [ IV ] Hydration of an alkene: The reaction of an alkene with water to produce an alcohol. Known catalysts include homogeneous systems such as phosphoric acid, silicic acid, and tungstosilicic acid, and heterogeneous solid acids such as WO ₃ , SiO ₂ ･Al ₂ O ₃ , and zeolites.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

一般に，ある化学種(イオン，無機化合物，有機化合物など)が水と結合することをいう．【Ⅰ】水中に溶解した荷電粒子(イオン，電子)が，そのまわりに1個以上の水分子を強く引きつけ，全体として一つの集団的性質を示すこと．イオンの場合は水和イオン，電子の場合は水和電子という．水和のとき水和エネルギーを放出する．粒子と水分子の間の相互作用は，電荷と水分子の双極子の間の静電引力による．電場の作用により，水和イオンまたは水和電子が移動するときには，荷電粒子は水和した水分子を引きつれて動くから，その移動度は水和の程度に依存する．たとえば，水溶液中のイオンの導電率は Li^＋ ＜ Na^＋ ＜ K^＋ の順で，これはイオン自身の大きさから期待される順序とは逆である．これは Li^＋ のように小さいイオンほど電荷と双極子の間の有効距離が小さく，したがって水和の程度が大きいためである．水蒸気の存在下で低圧の気体Xを電子衝撃するとき，イオン-分子反応により，X^＋ (H₂O)_n(nは整数)のような高次イオンができることが質量分析計で見いだされているが，これも水和イオンといわれる．【Ⅱ】イオンの空の軌道に水分子の非共有電子対が与えられれば，本質的には共有結合になり，たとえば [Co(H₂O)₆]^2＋ などができる．これも水和という．アクア化もこの一つである．【Ⅲ】無水物が結晶水を取り込むこと．[別用語参照]水和物【Ⅳ】アルケンの水和：アルケンと水の反応によりアルコールを生成すること．触媒には，リン酸，ケイリン酸，ケイタングステン酸などの均一系と，WO₃，SiO₂･Al₂O₃，ゼオライトなどの不均一系固体酸が知られている．

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