化學化程式問題...

鎂離子既化學式係Mg 電荷係2+
氫氧離子化學式係OH-
由於要平衡電荷 所以需要2個OH-
so 氫氧化鎂既化學式就係Mg(OH)2
因為OH係1個離子
所以要用括號括住佢
(OH)2係指2個氫氧離子
OH2就即係1個氧2個氫

因為OH-係一個離子，有1個O同1個H atom，你諗下，如囝我佢個化學式寫成

MgOH2，咁就代表呢個野有1個O同2個H atom，而正確係一個Mg(OH)2有2個O，2個H，

咁就係括號既重要性…有D 有機物化學式，有時都有括號，咁今次用法同之前講左既唔同

佢係代表「支鏈」所接駁的地方。eg
H CH3 H
| | | 佢既化學式可簡化為CH3CH(CH3)CH3
H - C - C - C - H
| | |
H H H

It is a must to add the bracket in the formula of Mg(OH)2 .
It's because a bracket is needed when quatity of the a cations or anions is more than 2,
in which these cations or anions are polyion,
eg. (NH4)2CO3, Mg(MnO4)2.
However, when the ions are not polyions, a bracket MUST NOT added.
eg. MgCl2, Na2O.
Besides, when the quatity of the of the polyions is 1, a bracket MUST NOT added.
eg, NaOH, MgCr2O7

你要當OH為一個單位，當雖要2個或3個OH時，你就要加括號。當你只雖1個OH時，就不要加括號。例如:NaOH , KOH , NH4OH, Mg(OH)2 , Ca(OH)2, Al(OH)3等