chemical formulae

第一題不應該也不可能如此約簡，
a) Hg2(NO2)2　Mercury(I) nitrite
The two Hg atoms are bonded together using the 6s orbitals. Mercury is unique in forming stable dinuclear metal ions. At Hg(+I) state, it consists of two directly linked metal atoms. The mercurous ion thus has the structure [Hg-Hg]2+.
In simple quantitative analysis, you can take HgR instead of Hg2R2 for simplicity (in calculation), but you have to be cautious that Hg+ is not likely to exist (at least in normal condition for observation).

第二題
a) Si2Br6　disilicon hexabromide

Ｂｒ　　Ｂｒ　　Ｂｒ
　＼　／　　　／
　　Ｓｉ－Ｓｉ
　／　　　／　＼
Ｂｒ　　Ｂｒ　　Ｂｒ

Si2Br6 can be produced by pyrolysis (strong heating). Moreover, other members of the series
Ｓｉ　Ｘ　　　　　can be produced by pyrolysis (strong heating).
　　ｎ　２ｎ＋２
These are either volatile liquids or solids.
SiBr4 + Si --> Si2Br6 + higher members of the series

第三題
NO2 the different from N2O4
NO2 Nitrogen dioxide
N2O4 Dinitrogen tetroxide

NO2 / N2O4 Tm = -11 deg C Tb = 21 deg C
N2O4 Dinitrogen tetroxide, the molecule is planar. The NO2 is obtained as a brown liquid which turns paler on cooling, and eventually becomes a colourless solid. This is because NO2 dimerizes into colourless N2O4. NO2 is an odd electron molecule, and is paramagnetic and very reactive. It dimerizes to N2O4, by pairing the previouly unpaired electrons. N2O4 has no unpaired electrons and is diamagnetic. It is also colorless but can appear brownish yellow liquid due to the presence of NO2 according to the following equilibrium:
N2O4 ＜＝＞ 2NO2
Higher temperatures push the equilibrium towards nitrogen dioxide.

2007-08-31 15:15:30 補充：
N2O4 Dinitrogen tetroxideＯ　　　　　Ｏ　＼　　　／　　Ｎ－Ｎ　／　　　＼Ｏ　　　　　ＯNO2 Nitrogen dioxide　Ｎ＝Ｏ　//Ｏ

第一題應該係答案b~
因為佢係ionic compound~佢既formula一定以simplest ratio去表達

第二題同第三題性質一樣
2)a 3)唔同

因為Si2Br6呢隻compound係covalent compound~
molecule唔會以最細整數比例去顯示
所以要跟番個名既描述 有二粒Si 六粒Br

而第三題~ 係唔同的 因為根本唔同結構~
不過原來nitrogen dioxide同 dinitrogen tetraoxide係有一個equilibrium relation
即係 2 NO2(g) <=> N2O4(g)