有些问题想请教(Form six chemistry)

Leong13

有些问题想请教 the different between ionic bond,covenlent bond , van der waals ,hydroden bond?

彌陀弟子

ionic bond[give and receive],covenlent bond[share]===atom and atom

van der waals ,hydroden bond[omly for water]=molecule and molecule

van der waals= permenent permenent dipole + temporary dipole[more shifT to permenent dipole]

[ Last edited by 彌陀弟子 on 22-2-2005 at 09:09 AM ]

雨天之魂

彌陀弟子 于 22-2-2005 09:08  说 :
ionic bond[give and receive],covenlent bond[share]===atom and atom

van der waals ,hydroden bond[omly for water]=molecule and molecule

van der waals= permenent permenent dipole + temporary dip ...

hydrogen bond -> hydroxyl group (-OH), NH3, HF.

van der waals -> dipole-dipole, dipole-induced dipole

ionic bond 和 covalent bond 是 atom 之间的 bonding,
hydrogen bond 和 van der waals 则是 molecule 之间的咯.

彌陀弟子

雨天之魂 于 22-2-2005 12:19 PM  说 :


hydrogen bond -> hydroxyl group (-OH), NH3, HF.

van der waals -> dipole-dipole, dipole-induced dipole

ionic bond 和 covalent bond 是 atom 之间的 bonding,
hydrogen  ...

不好意识...我要写..EXAMPLE FOR WATER的写成ONLY FOR WATER...

原粮我

我不明白甚么叫甚么是van der waals force n covalent bond . Both of them seem to be same very confusing . 有谁会explain 请帮帮忙 Brand Br is covant or var der waals and HCl is var der waals or covalent?Please show me some example or diagram please..........

BluStAr

covalent bond 是share electron.......他们是between atom..not molocule
就比如说.. NH3
N atom 1 s^2 2s^2 2p^3---5 electron in its outer shell
H atom 1s^1---1 electron in its outer shell
nitogen atom contributes 3 electron from its outer shell forming 3 N-H covalent bonds with 3 hydrogen bond.
就是说他们需要 share electron 来达到 stable....
重点是 share electron...可以是 single, double covalent bond, triple covalent bond

van der waals force is between molocule,n the substance will only exist as a gas.
有两种
1]permenent dipole-permenent dipole attractions--only for polar
2]temporary dipole-induced dipole attractions-- for Non-polar n polar..

HCL 跟 HCL 之间 是 van der waals
H  跟 CL 之间是covalent....因为他们都不是 metal...需要 share electron...

应该就是酱。希望没错。
有错等人来纠正！

BluStAr

hydrogen bond....
用比较 粗的解释就是， 当有一个 hydrogen bond... 他旁边有出现一个 strongly electronegative atom (F, O, H), 他们之间就会有hydrogen bond.....

X--H '''''Y(strongly electronegative atom)
      |
  hydrogen bond

n the strongly electronegative atom ...common we use F, O, H
juz remember this 3...
n only 1 lone pair from F, O, H can formed 1 hydrogen bond

van der waals < hydrogen bond < covalent bond

弹煮

BluStAr 于 26-2-2005 05:20 PM  说 :
(F, O, H)

是 F , O , N 吧？

BluStAr

弹煮 于 10-4-2005 02:04 AM  说 :

是 F , O , N 吧？

对哦....
不小心打错了。。。

kensai

看到上面的解释后，发掘少许错误，就让我来解释和整理把

1)when the difference of electrostatic charge of elements invovled in bonding is large, they form ionic bond,because the Electrons will move to more electro-ve site
,
2)When the difference of electrostatic charge of elements invovled in bonding is small, they don't form ionic bond, they form covalent bond, bcoz the elements don't have enuf energy to pull the electrons to 1 site, thus, they share electrons.


3）However,the elements invovled in some covalent bond don't have equal value of electro charge. THus, some electrons will tend to move slightly to the more -ve site of elements.
EG.
When hydrogen forms a bond with N,O,F. It gains a slight positive charge.This is because    N,O,F is more electronegative.This slight postive charge will form HYDROGEN BOND with the lone pair electrons of the atom with slight negative charge(NH3,Hcl or HF)

# Hydrogen bond is formed only when the molecules invovle Hydrogen with N,O,F

4)Given that N,O,F is very -ve elements.What happens to other elements with slight -ve charge??

The answer is  permanent dipole-dipole bond

EG. NACL with H2o

When NaCl ionizes in water, Cl- will attract to H(slight +ve) in H20

5)induced dipole bond= van deer waals forces
THis happens in almost every molecules. EG. oxygen gas, water,

Explanation: electrons spend 95% of their time in their orbitals, where is the other 5%??
The answer is the electrons sometimes will move out of their orbitals, moving to other place , like the orbitals of other molecule.When this happens, the certain particle in covalent bond will gain a slight +ve/-ve charge. This slight charge will induce the neighbour molecules.
This prinsip is similar to the " cas /nyahcas " we learn in fizik.

6) HOW about INTERMOLECULAR FORCES??
intermolecular forces = hydrogen bond,dipole-dipole,van deer waals

here got another question is Hydrogen bond always intermolecular forces???
NO, EG . in 2-phenol benzene and 4-phenol benzene.

There are hydrogen bond formed within the benzene molecule, this is not call intermolecular forces, but they are 'INTRAMOLECULAR FORCES", means happen inside a molecule, not between the molecules.


conclusion : giant covalent lattice (strongest compound with many covalent bonds)
             ionic (stronger bond)
             covalent(strong)
             hydrogen(weak)_________________________________________> THis 3 are
             permanent dipole-dipole(weaker)------------------------>  intermolecular
             temporary dipole/van deer waals (weakest bond) ----->  forces

如有错误，请更正！！谢谢！！

[ Last edited by kensai on 21-5-2005 at 03:32 PM ]

bluedog

vander waals forces
如果跟着syllabus的话，vander waals 是分成两种：
一是induced dipole（tremporary dipole),（for发non polar molecule或是symmetry 的polar molecule!)
一是permanant dipole(for polar molecule的！）

[ Last edited by bluedog on 16-5-2005 at 01:39 PM ]

bluedog

kensai 于 13-5-2005 09:27 PM  说 :
conclusion : ionic (strongest bond)
             covalent
             hydrogen____________________________________________> THis 3 are
             permanent dipole-dipole----------------------------->  intermolecular
             temporary dipole/van deer waals (weakest bond) ----->  forces

giant covalent lattice is strongest than ionic bond!!!!
for example,diamond is a giant covalent struture n posses a strong bond!!
u should say that ionic bond is stonger than simple covalent molecule!

kensai

aiya,忘记了还有一个 giant covalent lattice,哈哈，谢谢！

但是也不能说是 strongest bond 啊，只能说是 strongest compound with many covalent bond.

[ Last edited by kensai on 16-5-2005 at 06:29 PM ]

弹煮

kensai 于 13-5-2005 09:27 PM  说 :
When NaCl ionizes in water, NA+ will attract to H(slight +ve) in H20

Na+ 怎么会 attract to H+ 呢？

kensai

弹煮 于 21/5/2005 01:03  说 :

Na+ 怎么会 attract to H+ 呢？

谢谢纠正，
我又在打错字了，哈哈