Post by: hyperblade01 on June 15, 2009, 08:38:41 pm
Covalent > Ionic > Metallic ?
Yea, something that was done in year 11 - just not sure if ionic or metallic is the weakest.
Post by: TrueTears on June 15, 2009, 08:40:26 pm
Post by: hyperblade01 on June 15, 2009, 08:44:18 pm
Covalent - diamond
Ionic - ?
Metallic - you can bend and twist some metals easily
Post by: TrueTears on June 15, 2009, 08:47:27 pm
Post by: ilovevce on June 16, 2009, 01:18:33 am
In terms of bonding:
Covalent > Ionic > Metallic ?
In what way are you comparing the bonding?
There's no easy rule that ranks the 'strength' of various bonds, since we have no definition of 'strength' in a strict sense. The best thing you can do is understand how each bonding type relates to the properties of those materials.
To highlight the difficulties, here are a few examples:
-Diamond is one of the hardest substances known to man, meaning that it is incredibly difficult to scratch. However, a diamond could be shattered if hit hard enough with a hammer, due to the fact that it is brittle. Diamond will also combust in the presence of oxygen (albeit with a very high activation energy) to form carbon dioxide, because it is not the most stable compound that carbon could be in.
-Metal, compared to diamond, is not as hard (it is easy to scratch), yet if you hit metal really hard with a hammer it will not break, it will bend, due to its malleability. Metals also have a great deal of variation in terms of their reactiveness and melting points. Caesium will literally explode upon coming in to contact with water whilst gold will rarely react at all.
- Ionic lattices are again different. NaCl is very brittle and its crystals are easily scratched, but it is quite unreactive. Apply a flame to NaCl and it will not combust, nor will it melt. However, by simply placing NaCl in water, its ions will completely dissociate to form ligands with water.
This all shows that we might classify 'strength' in different ways. Ductility, hardness, melting points and chemical stability are all ways of comparing strength.
Now, to get technical, 'bond strength' or 'bond energy' is a property of any bond between atoms and refers essentially to the energy required to break that bond to form two radicals. This property is directly related to the chemical stability of a compound. So, the bond energy of a C-C bond is the energy required to split the bond and form two C radicals.
Properties like ductility and hardness are more related not to the strength of the bonds, but to the directional properties of the bonds. For example, the four carbon covalent bonds in diamond are very 'rigid' not allowing the carbon atoms much movement. The carbon will not deform at all under certain levels of stress, but after reaching a critical stress, the diamond will suddenly shatter. Metal, conversely, will bend at low levels of stress, but will rarely snap (and certainly not shatter). This is because the mobile electrons shared by the metal atoms can easily shift about and change position, allowing the atoms themselves significant movement.
Hope this clarifies, rather than confuses :D