General Chemistry Q

[vcuchic]

Hey Guys,

This question is straight out of Top Score..

Question:
Which of the following has an octet on the central atom?
ICl4+
SeF4
PBr4+
IF3
BrF4-


Answer:
PBr+

I don't even know how to approach this question...
Any help is greatly appreciated. Thank you so much in advance!

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[levyusupov]

first of all, the central atom is the least electronegative atom in the molecule.

second, count the valance electrons and draw the structure with the least electronegative atom, the central atom, in the middle.

third, spread the counted electrons.

thus PBr4+ will be:

P=5 ; Br= 7(4)=28

28+5-1=32 electrons to spread where one(1) is trefered to the + charge (electron lost).
Br
Br-P-Br
Br
each Br will get 6 (total 24) in addition to the four bonds that makes eight electrons, thus 32.

P has four bonds, therefore octet (8 electrons) is satisfied on the P.

 

[vcuchic]

you mean the central atom is the LEAST electronegative.

 

[levyusupov]

you mean the central atom is the LEAST electronegative.

sorry, you correct the least electronegative. i will fix it in the original post, thanks.

 

[STACM]

can someone explain how the other options DONT have an octet on the central atom?