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cyw1226 2012-7-2 10:48 PM

structures and properties of substances

Explain why iodine is a solid, bromine is a liquid, while chlorine and fluorine are gaseousat room conditions.


solution from publisher:
Iodine, bromine, chlorine and fluorine have a simple molecular structure and their molecules are held by weak intermolecular forces called van der Waals' forces. The larger the molecular size, the greater the van der Waals' forces. The molecular sizes of the substances are: I2 > Br2 > Cl2 > F2. Therefore, the strength of the van der Waals' forces are: I2 > Br2 > Cl2 > F2.



可能係我英文差:smile_o08:,

佢講 molecular sizes of the substances 係點搵出黎咖?

知道左 the strength of the van der Waals' forces are: I2 > Br2 > Cl2 > F2 之後就等於解釋左why iodine is a solid, bromine is a liquid, while chlorine and fluorine are gaseousat room conditions?

[[i] 本帖最後由 cyw1226 於 2012-7-2 10:57 PM 編輯 [/i]]

hk56740 2012-7-3 01:56 AM

[quote]原帖由 [i]cyw1226[/i] 於 2012-7-2 10:48 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=334359633&ptid=19771049][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
Explain why iodine is a solid, bromine is a liquid, while chlorine and fluorine are gaseousat room conditions.


solution from publisher:
Iodine, bromine, chlorine and fluorine have a simple molec ... [/quote]
period愈大,愈多層電子,個molecule咪愈大

jmlo 2012-7-3 03:06 AM

回覆 1# 的帖子

[quote] 佢講 molecular sizes of the substances 係點搵出黎咖? [/quote]
分子體積和總面積可以通過實驗方法(例如X射線晶體學)測量。

[quote] 知道左 the strength of the van der Waals' forces are: I2 > Br2 > Cl2 > F2 之後就等於解釋左why iodine is a solid, bromine is a liquid, while chlorine and fluorine are gaseousat room conditions? [/quote]
對,一般來說,物質的熔點跟分子間的引力(就是 van der Waals' forces)有關;引力越大,熔點越高。所以,fluorine 和 chlorine 是氣體,bromine 是液體,而 iodine 是固體。

cyw1226 2012-7-3 09:49 PM

咁the strength of the van der Waals' forces are: I2 > Br2 > Cl2 > F2  ----呢D資料係咪背書咖?:smile_27:

jmlo 2012-7-4 12:03 AM

回覆 4# 的帖子

其實是不需要背的。只要你記得范德華力 (van der Waals forces) 一般都是正比於分子的分子量和分子面積﹐很容易你就可以自己推導出 I2 > Br2 > Cl2 > F2。當然﹐這只適用于一般的情況﹐現實上還是有比較複雜而例外的例子。

Ron~ 2012-7-4 01:07 PM

資料唔洗背,因為van der Waals' force係會受一啲因素影響,eg total surface area of molecules, polarity of molecules
size of I2>Br2>Cl2>F2 因為I係period 5,Br係period 4...
要知道period越大,size越大(因為多左一層e-)->size of e- cloud越大-> e- cloud becomes more diffused and polarisable-> van der Waals' force 越大
資料唔洗背,但個關係就要明,識用番出黎

有個重要既概念,要知道subatomic particles越多,唔代表個size越大(呢個要打粒星啊,遲d教個時你就明)
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