| Author | Message | ||
     Samson Username: 981125 Registered: 04-2003 |
本中四書得兩個例子,HCl and H2O 我覺得好像大部份有H+ ion份的non-organic compound就係 請問正唔正確 又請問有無其他例子? | ||
| 951129 Username: 951129 Registered: 04-2003 |
Part 1 It is not true! Polar bond is the unequal sharing of the electron cloud between the bonding atoms. Every elements have a value called electronegativity, it show the ability of an atom to attract the bonding electrons. For example, HF has a polar bond and it is a polar molecule. Fluorine has the higher elecronegativity (4) but Hydrogen has the lower (2.1). Due to the difference of the electrnegativity, the electron cloud will shift to the Fluorine atom and causes it to have a small negative charge. And the Hydrogen atom has a small positive charge. (Hence, the bond carries a little ionic character.) CH4 also has polar bond (C-H), but it is a non polar molecule. It is because the dipole moment is cancelled out by the symmetric structure. | ||
| 951129 Username: 951129 Registered: 04-2003 |
Part 2 REMEMBER: all covalent bonds between atoms with different electronegativity MUST be polar bond. To determine whether the molecule is polar or not, the electronegativity and the structure of the bond should be considered. If the structure is symmetric, such as CH4, the dipole moment will be cancelled each others. It proved that why CH4 is non-polar although it is bonded by different electronegativity. H2O is in V-shaped, so it is a polar molecule. CHCl3 is a polar bond although it is symmetric in structure, but it is convalently bond by different atoms (different elecronegativity). SO2 is polar due to the V-shaped but CO2 is non-polar (linear in shape). Hope that u will understand what I mean. Please remind me if the above concepts are wrong. ^^…. | ||
| Samson Username: 981125 Registered: 04-2003 |
我上面講的 "我覺得好像大部份有H+ ion份的non-organic compound就係" 其實係講polar covalent molecule 因為hydrogen係唯一一個係period 1而可以form ion 所以佢同其他period的element form molecule而係non-organic的話 個molecule就係polar covalent molecule(個人覺得) 仲有想問pure water分別在高,普通,低電壓下通唔通電? 謝謝你的答案 | ||
| Inamoto5 Username: admin Registered: 04-2003 |
First of all, thanks about the good explanation of polar bond....but I think S.5 classmates do not know anything about dipole moment...^^ Samson イモ, you asked a question about polar covalent bond...but I don't know why you think that the polar covalent bond is related to H+ ion??... No ion is existed inside a covalent compound! You can read the explanation of 951129 (Mr Fong?) A part of assumption of Samson is alright...usually a polar bond is formed when a hydrogen atom combined with other atoms...do you know why? It's because the electronegativity of hydrogen is quite low so the bond formed between the hydrogen atom and other high electronegativity atoms is polar. However, please pay attention that a particular bond in a molecule may be polar but this doesn't mean that the molecule is polar molecule....for example CH3Cl is a polar molecule but CH4 is a non-polar one!! (Mr Fong has a very good explanation in this part, you read it yourself...) | ||
| Andrew Username: 951129 Registered: 04-2003 |
As I know, water can do electrolysis. So it may allow the current to pass through. Electrolysis of Water 4H2O + 4e- --> 4OH- + 2H2 cathode 2H2O --> O2 + 4H+ + 4e- anode ^^... | ||
| Inamoto5 Username: admin Registered: 04-2003 |
In normal case, water can rarely do electrolysis...A small amount of sulphuric acid should be added to increase the conductivity of water | ||
| Samson Username: 981125 Registered: 04-2003 |
咁又問一下 saturated, concentrated同dilute的糖水通唔通電? | ||
| Chio U Kim Username: cuk Registered: 04-2003 |
The model answer is No! No! No! But in real situations, all can conduct electricity to certain extent. | ||
| Samson Username: 981125 Registered: 04-2003 |
再問多個問題 如果溶些糖入一杯鹽水 會不會下降佢的導電性,好像叫conductivity 睇黎我個頭滿是問題 | ||
| Chio U Kim Username: cuk Registered: 04-2003 |
The conductivity is more or less the same. But if you add water to a sodium chloride solution, you will reduce the concentrations of sodium ions and chloride ions leading to a drop in conductivity. |