查看完整版本 : bonding angle

dustbus 2013-8-29 02:16 AM

bonding angle

what is the 3 dimensional structure of SF4??IT SHOULD be trigonal bypyramid??but how to draw the remaining electron pair:smile_41::smile_41:


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[[i] 本帖最後由 dustbus 於 2013-8-29 02:43 AM 編輯 [/i]]

jmlo 2013-8-29 12:34 PM

[quote] what is the 3 dimensional structure of SF4??IT SHOULD be trigonal bypyramid??but how to draw the remaining electron pair [/quote]
Recall the rule: Lone-pair bond-pair repulsion > bond-pair bond-pair repulsion.
Then you can determine the position of the lone pair so that the overall repulsion is minimum.

For your reference

[url]http://en.wikipedia.org/wiki/Sulfur_tetrafluoride[/url]

dustbus 2013-8-29 03:41 PM

haha thx

my book only mention six type of shape:linear,trigonal pyramid,V-shaped,tetrahedral,trigonal planar,trigonal bypyramid,octrahedral:smile_27: :smile_27:

THX JMLO CHING

chungkin81 2013-8-29 09:33 PM

I remembered how can we predict the molecular shape with lone-pair electrons by VSEPR at HKAL. For this example, I used my HKAL knowledge for prediction.

dustbus 2013-8-29 11:29 PM

haha thx ching  

now I can know more about the shape of molecule:loveliness: :loveliness: :loveliness:

Zzlaz 2013-8-30 12:20 PM

通常我叫佢做distorted tetrahedron / seesaw
因為佢個型好似個搖搖坂
兩個F做支點 兩個F 做塊版



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Zzlaz 2013-8-30 12:23 PM

回覆5 #的帖子

Mathematics

無lone pair electrons bond angle 基本確定

有的話 佢排斥力會拉窄左bond angle
令到佢變形

Methane同ammonia都有4個valence pairs (4,0) (3,1)
但methane係tetrahedral而ammonia係trigonal pyramidal



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dustbus 2013-8-30 01:40 PM

[quote]原帖由 [i]Zzlaz[/i] 於 2013-8-30 12:23 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=370548724&ptid=22370237][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
Mathematics

無lone pair electrons bond angle 基本確定

有的話 佢排斥力會拉窄左bond angle
令到佢變形

Methane同ammonia都有4個valence pairs (4,0) (3,1)
但methane係tetrahedral而ammonia係trigonal pyramid ... [/quote]

好似話lone pair唔佔shape佔空間

BTW THANK YOU!!

Zzlaz 2013-8-30 04:46 PM

回覆8 #的帖子

其實hkdse.這些題目唔值錢



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dustbus 2013-8-30 05:56 PM

haha 今年出左幾題,所以問下:loveliness: :loveliness:

當然最難都係ORGANIC CHEM果類:smile_27: :smile_27:

dustbus 2013-8-30 06:57 PM

btw in the structure of ice,why each water molecule forms four hydrogen bond tetrahedrally,why cannot form five bond



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Ron~ 2013-8-30 07:27 PM

[quote]原帖由 [i]dustbus[/i] 於 2013-8-30 05:56 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=370567411&ptid=22370237][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]haha 今年出左幾題,所以問下:loveliness: :loveliness: 當然最難都係ORGANIC CHEM果類:smile_27: :smile_27: [/quote]DSE,我覺得or chem偏易,最難既係elective既an chem



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jmlo 2013-8-31 12:08 AM

回覆 8# 的帖子

Molecular shape is labeled considering the spatial arrangement of atoms. Lone pairs of electrons are not taken into account as they are "invisible". However, the repulsion between lone pairs and bond pairs is not negligible; that's why you see the distortion of molecules when lone pair is present. (Good examples: CH4 and NH3 by Zzlaz in post #7)

jmlo 2013-8-31 12:17 AM

回覆 11# 的帖子

Atoms in first two rows (i.e., from H to Ne) cannot form more than 5 bonds at a time. More precisely, this observation is valid for the 2nd row p-blcok elements (B, C, N, O and F), and is usually attributed to the absence of low-lying accessible d-orbitals.

FYI: Certain compounds in which C and N form 5 bonds (or in other words, 5-coordinate) have already been made in 90's. So, the restriction discussed above is not always right. There are exceptions!

dustbus 2013-8-31 12:31 AM

[quote]原帖由 [i]jmlo[/i] 於 2013-8-31 12:17 AM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=370590949&ptid=22370237][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
Atoms in first two rows (i.e., from H to Ne) cannot form more than 5 bonds at a time. More precisely, this observation is valid for the 2nd row p-blcok elements (B, C, N, O and F), and is usually attr ... [/quote]

haha thx for explanation:smile_35::smile_35:

This topic looks like very interesting

jmlo 2013-8-31 12:49 AM

回覆 15# 的帖子

The debates about the existence of 5-coordinate C, N and O compounds (or hypervalent compounds, the proper name given to this types of compounds), and their bondings have been around for many years. While many chemists believe and use VSEPR theory, some indeed oppose and use other bonding models (e.g. MO theory) instead to explain the geometries of molecules.

dustbus 2013-8-31 07:21 PM

thx:loveliness: :loveliness: :loveliness: :loveliness:

Zzlaz 2013-9-1 06:48 PM

[URL=http://s1080.photobucket.com/user/koalatsi/media/strate.png.html][IMG]http://i1080.photobucket.com/albums/j324/koalatsi/strate.png[/IMG][/URL]

MATHS.
TO SHOW 109.5'

dustbus 2013-9-1 09:27 PM

lol chem with math,thx all of you so much><

btw

why ClF3 cannot have 3 different shape?There are three different ways in which we may arrange the 3 bonding pairs and 2 lone pairs into a trigonal bipyramid: trigonal pyramid,trigonal planar and T-shape
this 3 type is reasonable,but why T-shape is the shape of ClF3

jmlo 2013-9-2 12:08 AM

回覆 19# 的帖子

Note that there are three Cl-F bond pairs and two lone pairs around Cl in ClF3. Therefore, the choice of trigonal pyramid can be ruled out right away.

Both trigonal bipyramid and T-shape are acceptable for 5-coordinated compounds/complexes (i.e., a atom that forms five bonds at a time). To determine which geometry is more favorable, we have to recall that
lp-lp > lp-bp > bp-bp
Then count all possible repulsion pairs in these structures:

(a) trigonal bipyramid
6 x lp-bp @ 90 degrees
3 x bp-bp @ 120 degrees
1 x lp-lp @ 180 degrees

(b) T-shape
4 x lp-bp @ 90 degrees
2 x lp-bp @ 120 degrees
2 x bp-bp @ 90 degrees
1 x lp-lp @ 120 degrees

Comparing all these, we can see that T-shape has one less bp-bo repulsion, and the more compressed bp-bp (120 to 90) can be compensated by the release of lp-bp (from 90 to 120) because lp-bp is stronger than bp-bp. Finally, the trigonal bipyramid has one additional bp-bp @ 120 degrees while the T-shape has a lp-lp @ 120 degrees. The difference in stability can be offset by the energy gain due to the release of lp-bp in the T-shape (as we calculated above). Therefore, the overall stability of T-shape is higher than that of trigonal bipyramid.

Note that this is just a simple VSEPR account of the geometry of ClF3. You might find exceptions for other compounds of the same types. Don't panic. It's just chemistry!

dustbus 2013-9-2 12:21 AM

This topic is very interesting,but my book only mention 6 type of shape(linear,V-shape,trigonal pyramid,trigonal planar,tetrahedral,trigonal bypyramid and octahedral),that is the syllabus of DSE.BUT I want to know more about the shape.By the way,thx for teaching:):):)

jmlo 2013-9-2 05:14 AM

回覆 21# 的帖子

Indeed it is interesting to explain molecular shapes with VSEPR theory, although detailed analysis as that in post 20# is not necessary. But, at the end, it is not bad to learn, right? :loveliness:

Zzlaz 2013-9-2 07:25 AM

回覆8 #的帖子

那點解你仲話佢有機會係trigonal bipyramidal呢



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dustbus 2013-9-2 08:24 PM

[quote]原帖由 [i]Zzlaz[/i] 於 2013-9-2 07:25 AM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=370753299&ptid=22370237][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
那點解你仲話佢有機會係trigonal bipyramidal呢



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my typing mistake lol,I want to type tetrahedral:'):'):')
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