Lewis acids & bases

1)路易斯酸 是接收孤電子對
路易斯鹼 是提供孤電子對
考慮酸平衡
HA+H2O-->H3O+ + A- HA是酸
F- 體積比Cl-細,Cl-能更有效分散負電荷(較穩定),使平衡位置在右方,酸性較高
Cl-較F-穩定代表HCl較HF不穩定 (平衡相對性)
所以可理解HCl較易接收接收孤電子,較強路易斯酸
所以I岩
同樣也可理解F-較易提供孤電子對,所以F-是較強路易斯鹼
F-是較強路易斯鹼,F2也是較強路易斯鹼
所以2都岩
F2是較強路易斯鹼,代表其離子也是較強路易斯鹼,代表HF是較弱路易斯酸所以statement 2 is the correct explanation for that hydrofluoric acid is a weak acid in water2)化學反應定義是有新物質生成
I.Ammonia dissolve in water 有
NH3溶水 NH3(g)-->NH3(aq)
NH3和水發生化學反應
NH3+H2O-->NH4+ + OH-
生成新物質NH4+ OH-II.Hydrochloric acid dissolve in water 有
HCl溶水 HCl(g)-->HCl(aq)
HCl和水發生化學反應
HCl+H2O-->H3O+ + Cl-
生成新物質 H3O+ Cl-III. Sodium hydroxide dissolve in water 沒有
NaOH溶水
NaOH(s)-->Na+(aq)+OH-(aq)
它和水沒有反應3)不會,h+ 會形成h3o+,是因為h+體積太小,和水結合的水合能很高
結合形式是h2o的孤電子對和h+的低能量空軌態形成配位共價鍵
oh-不會形成,因為體積大,h沒有能量空軌態,
而水的h也沒有能量空軌態

2012-05-14 18:28:28 補充：
體積大，軌態(orbital)也越大，自然容納兩粒孤電子的空間較大，電子密度(charge density)也越小，電子密度可理解成電子在軌態的密度，越高，孤電子越容易提供，越低，電子越難提供

事實上，鍵能（bond energy)同酸鹼離解度，沒有直接關係，因為鍵能主要是影響活化能(Ea),而主要影響因素，是離子的穩定性，考慮以下平衡

2012-05-14 18:28:32 補充：
NH3+H2O-->NH4+ + OH-
NH3+H2O--->NH2- + H3O+
OH-比NH2-穩定得多，所以反應二基本下會進行，可假設NH3只作鹼（BASE)就可
O en > N en ,抓住孤電子能力大，所以較穩定
這不用體積解釋，是因為同周期體積變化小，只考慮En就可
而同族就用體積解釋，因為由上至上，體積變化很大，這影響遠遠大於En

估計NH3+H2O-->NH4+ + OH-
是吸熱反應，因為離解常數低 Kb=1.8x10^-5

2012-05-14 18:33:13 補充：
OH-比NH2-穩定得多，所以反應二基本不會進行，可假設NH3只作鹼（BASE)就可
O en > N en ,抓住孤電子能力大，所以較穩定

2012-05-14 18:33:52 補充：
這不用體積解釋，是因為同周期體積變化小，只考慮En就可
而同族就用體積解釋，因為由上至下，體積變化很大，這影響遠遠大於En

2012-05-14 23:27:39 補充：
離解常數是由能量決定的
在很多平衡反應中，反應物也有足夠能量克服Ea，進行正向反應
所以在這情況下比較離子穩定性，就可

而不用考慮反應物的en，這是動力學（速率）的因素

The following is ONLY the TRANSLATED piece of answer from 小云
I’m not sure about its correctness!
Things in [ ] are my opinion/supplement

Here you are:

1) Lewis acid accepts lone pair of electrons
Lewis base donates lone pair of electrons

2012-05-12 17:55:59 補充：
Concerning the dynamic equilibrium of acid HA
HA + H2O <----> H3O+ + A-

As F- ion is smaller than Cl- in size,
Cl- can have a more even distribution of negative charge [which is from electrons]

2012-05-12 17:56:23 補充：
This make Cl- more stable [than F-],
So, the equilibrium position lies [more] on the right [for “HCl + H2O <----> H3O+ + Cl-” than “HF + H2O <----> H3O+ + F-”]

2012-05-12 17:56:35 補充：
[Thus, there will be more H3O+ in the equilibrium of hydrochloric acid than that of hydrofluoric acid]
[Such that hydrochloric acid is] more acidic [than hydrofluoric acid]

2012-05-12 17:57:09 補充：
Cl- is more stable than F-
means that HCl is less stable than HF [“平衡相對性”, I don’t know what is it = =]
Which can be understood as HCl accepts electrons better and thus is a stronger Lewis acid

So, statement I is correct

2012-05-12 17:58:06 補充：
{In the same sense,
F- donates lone pair of electrons [easier than Cl-]
So, F- is a stronger Lewis base [than Cl-]
F- is a strong Lewis base
And F2 is also a strong Lewis base
So, 2 is correct

2012-05-12 17:58:16 補充：
F2 is also a strong Lewis base means that its ions are also strong Lewis base,
Thus, it means that HF is a weak Lewis acid
So, statement 2 is the correct explanation for that hydrofluoric acid is a weak acid in water.}

[Things in{} are quite confusing, not really know what they means]

2012-05-12 17:58:27 補充：
2)
Definition of chemical reaction is that there are new substance(s) formed
I. Ammonia dissolve in water
New substance formed
NH3 dissolve in water: NH3(g)-->NH3(aq)
NH3 then react with water: NH3+H2O-->NH4+ + OH-
New substances formed : NH4+ and OH-

2012-05-12 17:58:56 補充：
II. Hydrochloric acid dissolve in water
New substance formed
HCl dissolve in water: HCl(g)-->HCl(aq)
HCl then react with water: HCl+H2O-->H3O+ + Cl-
New substances formed : H3O+ and Cl-

2012-05-12 17:59:02 補充：
III. Sodium hydroxide dissolve in water
No new substances formed
NaOH dissolve in water: NaOH(s)-->Na+(aq)+OH-(aq)
It has no reaction with water

2012-05-12 17:59:23 補充：
3)
No [OH- won’t form covalent bonds with water as H+ does]
H+ forms H3O+ is because the size of H+ is too small that the hydration energy is very high
The way of combining [H+ and H2O] is:

2012-05-12 17:59:36 補充：
Lone pair of H2O forms dative covalent bond[=coordinate bond] with the low-energy empty orbital of H+
OH- won’t form [covalent bonds with water as H+ does]

2012-05-12 18:00:13 補充：
Because it is large, [and its] H [atom] have no [low-energy] empty orbital, neither do the H atom[s] of water.

[I don’t quite understand what’s it saying for Q3]


That's all, hope I can help you =]