Generally, the bond formed between a metal atom and a non-metal atom is that of an ionic bond. The metal atom will transfer its valence electron(s) to the non-metal atom such that both will become cation and anion respectively. In this manner, both will attain the favourable octet.
While, the bond between two non-metal atoms is that of a covalent bond. Neither atoms is willing transfer electrons to each other, hence to obtain the favourable octet both atoms would share a certain number of valence electrons. This sharing can take place when the atomic orbital of both atoms overlap.
(A) Seemingly ionic compound but are actually covalent.
AlCl3 has covalent bonds between Al and Cl. This is contrary to what is expected.
If AlCl3 was a ionic compound, the Al3+ cation is small and has a large charge, hence this cation is willing to polarise the electron cloud of the anion.
Cl- is a large anion whose electron clouds are easily polarised. Polarisablity refers to the ease of distorting the electron cloud. When place next to Al3+, the electron cloud of Cl- is distorted by Al3+. This severe distortion allows for both electron clouds to overlap. When that happens it mimics the overlapping of orbital hence covalent bond is formed.
Interesting, in a single molecule of AlCl3, its dot and cross diagram does not fulfill the octet rule. This is because Al has only 3 valence electrons and even when all three are shared, there is only 6 electrons around Al. Hence, I must stress that this is not the norm. Usually, this rule is satisfied.
(B) Covalent bonds that carries some charge.
The assumption of a covalent bond is that the shared electrons are equally shared. This idea also suggests that the distance between the nucleus of one atom and the shared electrons is the same. However, this is not the case. Different elements' nucleus has different attractive power; some are more abled to pull electrons towards itself and hencce the term "electronegativity is introduced."
When the atom is more electronegative, it pulls the electrons closer to it. Hence when two atoms of differing electronegativity are bonded together, the atom which is more electronegative will pull the shared electrons closer to it.
This results in the less electronegative atom to carry a slight positive charge, while the other atom carries a slight negative charge. Since there is a small slight charges being produced,the two atoms are further held together because of electrostatic attraction between the partial charges.
In conclusion, we still need to bear in mind that the electrons are still shared between the two atoms; it is just now the shared electron is found closer to one nucleus than to the other. Therefore, a polar covalent bond is produced.
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Article written by Kwok YL 2009.
While, the bond between two non-metal atoms is that of a covalent bond. Neither atoms is willing transfer electrons to each other, hence to obtain the favourable octet both atoms would share a certain number of valence electrons. This sharing can take place when the atomic orbital of both atoms overlap.
(A) Seemingly ionic compound but are actually covalent.
AlCl3 has covalent bonds between Al and Cl. This is contrary to what is expected.
If AlCl3 was a ionic compound, the Al3+ cation is small and has a large charge, hence this cation is willing to polarise the electron cloud of the anion.
Cl- is a large anion whose electron clouds are easily polarised. Polarisablity refers to the ease of distorting the electron cloud. When place next to Al3+, the electron cloud of Cl- is distorted by Al3+. This severe distortion allows for both electron clouds to overlap. When that happens it mimics the overlapping of orbital hence covalent bond is formed.
Interesting, in a single molecule of AlCl3, its dot and cross diagram does not fulfill the octet rule. This is because Al has only 3 valence electrons and even when all three are shared, there is only 6 electrons around Al. Hence, I must stress that this is not the norm. Usually, this rule is satisfied.(B) Covalent bonds that carries some charge.
The assumption of a covalent bond is that the shared electrons are equally shared. This idea also suggests that the distance between the nucleus of one atom and the shared electrons is the same. However, this is not the case. Different elements' nucleus has different attractive power; some are more abled to pull electrons towards itself and hencce the term "electronegativity is introduced."
When the atom is more electronegative, it pulls the electrons closer to it. Hence when two atoms of differing electronegativity are bonded together, the atom which is more electronegative will pull the shared electrons closer to it.
This results in the less electronegative atom to carry a slight positive charge, while the other atom carries a slight negative charge. Since there is a small slight charges being produced,the two atoms are further held together because of electrostatic attraction between the partial charges.
In conclusion, we still need to bear in mind that the electrons are still shared between the two atoms; it is just now the shared electron is found closer to one nucleus than to the other. Therefore, a polar covalent bond is produced.-- -- -- -- --
Article written by Kwok YL 2009.
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