Which do not obey the octet rule?
Check all that apply.
CO2
IO3−
BH3
BF4−
XeF2
IO3− and XeF2
The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a full outer electron shell of eight electrons (except for hydrogen, which only needs two electrons).
Let's check each molecule or ion to see if it obeys the octet rule or not:
CO2:
Carbon (C) shares two electrons with each oxygen (O), resulting in a double bond. Each atom in CO2 satisfies the octet rule. Therefore, CO2 obeys the octet rule.
IO3−:
Iodine (I) is in the center and is bonded to three oxygen (O) atoms. The iodine atom (I) does not satisfy the octet rule since it has more than eight electrons around it. IO3− does not obey the octet rule.
BH3:
Boron (B) is in the center and is bonded to three hydrogen (H) atoms. Boron (B) only has six electrons around it, which is less than eight. BH3 does not obey the octet rule.
BF4−:
Boron (B) is in the center and is bonded to four fluorine (F) atoms. Boron (B) has six electrons around it, which is less than eight. BF4− does not obey the octet rule.
XeF2:
Xenon (Xe) is in the center and is bonded to two fluorine (F) atoms. Xenon (Xe) has eight electrons around it, which satisfies the octet rule. XeF2 obeys the octet rule.
In summary, the molecules or ions that do not obey the octet rule are IO3−, BH3, and BF4−.