Something about chemical bonding?

Question

The first one: Covalent Bonding

firstly, about Nitrogen. The pair of atoms are bonded to each other by triple covalent bond. Any more info on that particular bond?

Second qn: Ionic bond

Aluminium flouride has a higher melting point(1291 C) than aluminium chloride(180 C) Why??

Answer 1

Adding to Gervald's good answer, there are a couple crucial things that I think should be mentioned here. Most importantly, I'm going to tailor the answer to the (most likely) level of the asker.

Question One:

There are three bonds between the two nitrogen atoms. One sigma bond, bonded end-to-end between two p-orbitals:

O N O ---- O N O

and two pi bonds, bonded adjacently, one each between the two remaining p-orbitals:

O ` , | ` , O ` , ` , ` ,
N ` , ` , ` N ` , ` , x2
O ` , | ` , O ` , ` , ` ,

** forgive the noisy drawing... I had to include the ` , ` , ` , as filler.

Each bond contributes a certain amount of electron density to the space between the nitrogen atoms. Because there are three bonds (rare in nature) there is a very high electron density between the two Nitrogen atoms, and thus, a correspondingly high negative charge.

Coulomb's law indicates that there is a great attraction between the highly negative center (I say "center" because, although it's technically attracted to the electrons no matter where they are, these electrons are only important for our discussion when they occur between the two N atoms, which is statistically most common), and protons of the N nuclei. It looks like this:

N+ { - } +N

This attraction decreases the bond length, and increases the amount of energy required to break the bond (called the "bond enthalpy").

Also, it should be noted that the entire nitrogen-nitrogen triple bond is non-polar, because neither nitrogen pulls *more* on the electrons than the other nitrogen.

As far as the second question, I think Gervald answered it well enough!

Happy Chem'ing :o)

Romi Strub, University of Waterloo - 2A Nanotechnology Engineering

Answer 2

N2 has the highest bond enthalpy of any bond, and this is responsible for the fact that we still, after millions of years, have 80% N2 in the atmosphere.

AlF3 is best considered ionic, with a high melting point. AlCl3 is best considered covalent and molecular, with a correspondingly low melting point (it sublimes on heating).

Answer 3

It broken