exceptions to octet rule

[imo92]

I was going through my chemistry text book and found a paragraph about exceptions to octet rule. it says that in PCl5 phosphorus breaks the octet rule because it has empty orbital 3d. then it shows an elocton con figuration:

1s2 2s2 2p6 3s2 3p2 3d0. in an earlier chapter it states that before 3d can be filled 4s has to be filled as 3d has more energy. i'm confused here can someone plz help. thnx alot

[hermanntrude]

the 3d and 4s subshells are very close in energy so sometimes the order gets a bit confused. For instance, when adding electrons in the aufbau (building up) process, we say that the 4s subshell is filled before the 3d subshell. BUT when you come ionise a transition metal the electrons are lost from the 4s subshell first.

 

Actually, though, it's more complicated than that. My advice is for you to wait until your course covers orbital hybridisation. This subject explains it all very nicely. However if you cant wait, try googling the topic.

[jdurg]

Good advice hermann. One needs to remember that chemistry is VERY complex, yet VERY simple at the same time. When one learns chemistry, they are typically taught very basic principles and concepts as starting out with quantum theory and the like will make it near impossible to understand. As a result, in the beginning a lot of "simplified" concepts are taught which need to be adjusted as your learn abou the more complex topics. Again, this is only so that you'll be able to learn it. It's not a flat out lie.

[Riogho]

The 4s subshell tends to be a little bit lower in energy due to a couple things. The electrons from the lower orbitals 'shield' the positive nuclear charge from seeing the outer 3d electrons as much, which causes them to be less attracted to it. Also, the 4s electrons are closer to the nucleus and therefore travel around them at higher speeds adding some relativistic effects to the electrons. All in all, the theory you want to look into is "Molecular Orbital Theory".

[elmejor]

I was going through my chemistry text book and found a paragraph about exceptions to octet rule. it says that in PCl5 phosphorus breaks the octet rule because it has empty orbital 3d. then it shows an elocton con figuration:

1s2 2s2 2p6 3s2 3p2 3d0. in an earlier chapter it states that before 3d can be filled 4s has to be filled as 3d has more energy. i'm confused here can someone plz help. thnx alot

 

Atomic No. of Phosphorous is 15, so the electronic config. will be 2, 8, 5

to complete its Octate three more electrons are required, and in the same way,

Chlorines atomic no. is 17, so the elec. config would be 2, 8, 7

 

Here, Chlorine requires 1 electron to complete its octate, therefor chlorine will take electrons from the other element and phosphorous will also take three electrons from the other element. And this can be done by sharing of electrons and this kinda sharing is always happens in Non-Metals

So in PCl5 sharing of electrons will take place.

[hermanntrude]

elmejor, i'd like to give you some advice now.

 

first, why not go and introduce yourself in the introductions thread if you havent already done so. welcome to the forum

 

second, when answering people's questions, check to see how old the questions are and whether they've already been answered. We value your responses but this one particularly was unhelpful. the question was already answered fully, and your response was only confusing the issue