Question

I know that the answer is ClF3...but I don't know why??

Which of the following contains an atom that does not obey the octet rule?
ICl
ClF3
KBr
CO2

Answer 1

do u know how to draw Lewis dot structure?

Answer 2

if you draw Lewis dot structure for all of those, you will see that total number of electrons surrounding the main atom would be 8
only one of them will have more then 8 electrons, these compounds are electron efficient compounds thus they do not obey octet rule :)

Answer 3

ICl - covalent compound thus sharing electrons, each atom will be surrounded by 8 electrons
KBr - ionic compound thus one of the atoms which is Br will be surrounded by 8 electrons
CO2- covalent compound thus sharing electrons and so all atoms will be surrounded by 8 electrons
now ClF3
Cl has 7 electrons in the last shell, F has also 7 electrons in the last shell
as we see there 3 bonds in this compound so that means 3 electrons of Cl are used in bonding to F, while 1 electron of each F is used to make this bond with Cl
so basically saying if 3 electrons of Cl is used in bond, 4 electrons are left right? (out of 7)
and now when the bond happens between Cl and 3 F atoms then these 3 electrons that are involved in bonding from Cl side would get doubled right? since 3 more electrons are coming from 3 F atoms (1 from each)
so it'll be in total 6 electrons surrounding Cl right?
now these 6 electrons + 4 electrons of Cl that were not involved in bonding would in total give you 10 electrons
10 electrons is more then 8, means it has 2 more electrons thus these kind of compounds are electron efficient compounds
because they have more then 8 electrons they do not obey octet rule :)

Answer 4

this is dot structure :)

Answer 5

by the way, if the electrons are less then 8 then that'll be electron deficient compounds and they also do not obey octet rule, example can be BF3

Answer 6

thank you!

Answer 7

@Somy would you mind looking at my other question?

Answer 8

@merimonkey you are welcome :D already did :)