Which compound is an exception to the octet rule?
$H _2 O$
HCl
$CCl _4$
$ClF _3$
Answer (2)
The octet rule states that atoms are most stable when surrounded by eight valence electrons.
Examine each compound to determine if it follows the octet rule.
H 2 O , H Cl , and CC l 4 follow the octet rule.
Cl F 3 does not follow the octet rule because the central chlorine atom has 10 electrons.
The compound that is an exception to the octet rule is Cl F 3 .
Explanation
Understanding the Octet Rule We need to identify the compound that does not follow the octet rule. The octet rule states that atoms are most stable when surrounded by eight valence electrons. We will examine each compound to determine if it follows the octet rule.
Analyzing Each Compound
H 2 O : Oxygen is the central atom. Oxygen has 6 valence electrons. It forms two bonds with hydrogen atoms, contributing 2 more electrons. Thus, oxygen has 6 + 2 = 8 electrons. It follows the octet rule.
H Cl : Hydrogen is bonded to Chlorine. Hydrogen has 1 valence electron and forms one bond with Chlorine. Hydrogen follows the duet rule (2 electrons). Chlorine has 7 valence electrons and forms one bond with Hydrogen, contributing 1 more electron. Thus, Chlorine has 7 + 1 = 8 electrons. It follows the octet rule.
CC l 4 : Carbon is the central atom. Carbon has 4 valence electrons. It forms four bonds with chlorine atoms, contributing 4 more electrons. Thus, carbon has 4 + 4 = 8 electrons. It follows the octet rule.
Cl F 3 : Chlorine is the central atom. Chlorine has 7 valence electrons. It forms three bonds with fluorine atoms, contributing 3 more electrons. Thus, chlorine has 7 + 3 = 10 electrons. It does not follow the octet rule.
Conclusion Therefore, Cl F 3 is an exception to the octet rule because the central chlorine atom has 10 electrons around it, exceeding the octet.
Examples
The octet rule is a fundamental concept in chemistry that helps predict how atoms will bond to form molecules. Understanding exceptions to the octet rule, like in Cl F 3 , is crucial for designing new molecules with specific properties. For example, in drug design, knowing how atoms can exceed the octet rule allows chemists to create molecules that can interact with biological targets in unique ways, potentially leading to new and more effective medications. Similarly, in materials science, understanding these exceptions can aid in the development of novel materials with tailored electronic or optical properties.
Cl F 3 is the compound that is an exception to the octet rule because it has 10 electrons around the central chlorine atom, exceeding the typical eight. The other compounds analyzed ( H 2 O , H Cl , and CC l 4 ) all conform to the octet rule. Therefore, the chosen option is Cl F 3 .
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