查看完整版本 : CHEM question (m.p and b.p)

ben1046 2013-10-19 07:45 PM

CHEM question (m.p and b.p)

A question: why the temp of M.p and b.p in Mg is higher than C?
but i checked on website , C is higher than Mg ,

dustbus 2013-10-19 09:58 PM

C is giant covalent structure:loveliness:

↗亢龍無悔↙ 2013-10-19 10:28 PM

[quote]原帖由 [i]dustbus[/i] 於 19-10-2013 09:58 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=374015363&ptid=22575845][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]C is giant covalent structure:loveliness: [/quote]Mg 夠有giant metallic structure 囉



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dustbus 2013-10-19 11:17 PM

[quote]原帖由 [i]↗亢龍無悔↙[/i] 於 2013-10-19 10:28 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=374017540&ptid=22575845][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
Mg 夠有giant metallic structure 囉



[img]http://i.discuss.com.hk/d/images/r10/androidD.jpg[/img] [/quote]
lol:smile_40::smile_40:

you win
maybe you need a lot of energy to break the network of covalent bond between the carbon atom:smile_41:

↗亢龍無悔↙ 2013-10-20 12:13 AM

[quote]原帖由 [i]dustbus[/i] 於 19-10-2013 11:17 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=374021328&ptid=22575845][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]lol:smile_40::smile_40:you winmaybe you need a lot of energy to break the network of covalent bond between the carbon atom:smile_41: [/quote]言下之意,即係energy breaking electrostatic force一定比較細?:smile_04:



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jmlo 2013-10-20 01:29 AM

回覆 5# 的帖子

Indeed, covalent bond is also based on electrostatic attraction between nuclei and electrons. :loveliness:

dustbus 2013-10-20 12:44 PM

[quote]原帖由 [i]↗亢龍無悔↙[/i] 於 2013-10-20 12:13 AM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=374026708&ptid=22575845][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
言下之意,即係energy breaking electrostatic force一定比較細?:smile_04:



[img]http://i.discuss.com.hk/d/images/r10/androidD.jpg[/img] [/quote]

我意思係指:smile_40::smile_40:

唔可以就住giant covalent structure同giant ionic structure去比較佢地既mp.bp

係咪C既covalent bond好多:smile_41::smile_41:要BREAK曬佢先溶到,所以要多D ENERGY:smile_41::smile_41:

jmlo 2013-10-20 01:47 PM

[quote] 唔可以就住giant covalent structure同giant ionic structure去比較佢地既mp.bp [/quote]
You are right. Metals span a wide range of mp and bp (e.g. osmium versus cesium).

[quote] 係咪C既covalent bond好多要BREAK曬佢先溶到,所以要多D ENERGY [/quote]
The difference in mp and bp is not solely related to the number of bonds between atoms in these substances. You have to look at the strengths of these bonds. C-C covalent bond is indeed very strong because of a good orbital overlap between C atoms.

↗亢龍無悔↙ 2013-10-21 08:41 AM

回覆6 #的帖子

打漏左,我係想講佢個意思係covalent bond 嘅electrostatic force 一定會比metallic bond 嘅electrostatic force強



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dustbus 2013-10-21 11:21 PM

WHY C=C bond lead to very reactive:smile_41:


and under wt condition the compound can be miscible in organic solvent:funk::funk:

[[i] 本帖最後由 dustbus 於 2013-10-21 11:35 PM 編輯 [/i]]

jmlo 2013-10-22 01:19 PM

回覆 10# 的帖子

[quote] WHY C=C bond lead to very reactive [/quote]
C atoms in C=C bond are not saturated. The pi orbitals overlap less effectively than the sigma orbitals do; therefore the resulting pi bond is more fragile than C-C sigma bond. It explains why the pi electrons are very reactive towards electrophiles.

[quote] under wt condition the compound can be miscible in organic solvent [/quote]
Do you mean dissolving alkenes in organic solvents?

dustbus 2013-10-22 07:31 PM

Do you mean dissolving alkenes in organic solvents?

no

i mean the compound under wt condition can dissolve in organic solvents, such as Cl and Br

jmlo 2013-10-26 11:50 AM

回覆 12# 的帖子

General rule: polar dissolves polar, and non-polar dissolves non-polar.

dustbus 2013-10-30 12:17 AM

C atoms in C=C bond are not saturated. The pi orbitals overlap less effectively than the sigma orbitals do; therefore the resulting pi bond is more fragile than C-C sigma bond. It explains why the pi electrons are very reactive towards electrophiles.

because my chemical knowledge is limited(pi orbitals and sth else seems out C of CHEM):smile_30: :smile_30: I don't understand what ching mean

BUT THX :loveliness:

jmlo 2013-10-30 08:49 AM

Is the section about sigma- and pi-orbitals already out of syllabus now? :funk:

Simply speaking, C prefers to form four sigma bonds with other atoms. In alkene molecules, C atoms in double bond unit form only three sigma bonds. Because of that, these C atoms are relatively unstable. In other words, they are reactive. They like to react with other species so that one more sigma bond can be formed.

dustbus 2013-10-30 08:21 PM

yes...all orbital out C:funk: :funk: :funk:
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