Octet Rule and Stability of Atom

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What is the Octet Rule?

The octet rule states that atoms gain stability when its outer valence shells comprise eight electrons. What does octet rule mean is that atoms of the main elements develop a tendency in participating in chemical bonding that the resulting molecule of every atom contains eight electrons in the valence shells. What does the octet rule state, is that the main group of elements only participate in the process The molecules of carbon, oxygen, nitrogen and halogen follow the octet rule. So, what is the definition of octet rule? Here, we see certain elements that obey this rule that include s-block and p-block elements hydrogen, helium and lithium are elements with exceptions to the octet rule. 

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What is the Octet Configuration?

What is octet configuration, can be understood from the arrangement of electrons in the outermost shells. The atoms are seen to have 8 electrons in the exterior shells. The following electron configuration explains this phenomenon.

ns² np⁶


What is an Octet?

To understand what is an octet formation in Chemistry, we need to know the electron arrangement. If the outermost shell forms an eight-electron arrangement, it is known as an octet. In other words, an octet of electrons is the same. This octet structure is responsible for inertness of most noble gases. 


What are the Octet Rule Examples? 

There are a few examples that follow the chemical bonding of atoms in compliance with the octet rule and this can be observed in the given subsection. 


NaCl (Sodium Chloride)

  • The compound NaCl features an ionic between the electropositive ion sodium (Na⁺) and electronegative ion chloride (Cl⁺). 

  • The chlorine atoms contain 7 electrons in its valence shell and it requires only a single atom to form an octet. 

  • The exterior shell of sodium contains a single electron. If this electron is lost, the second shell turns into a valence shell (which is already packed with 8 electrons). Therefore, the Na+ ion is more stable than metallic sodium. 

  • The chloride anion and sodium anion forms an ionic bond. The results in a molecule showing an octet configuration for both the participating ions. 

MgO (Magnesium Oxide)

  • The elements like magnesium and oxygen form a bond which is ionic. 

  • A stable configuration of neon is achieved when magnesium loses its two electrons. This helps in the formation of Mg⁺. 

  • Likewise, oxygen obtains two electrons that leads to the formation of the O²⁻

  • These two ions participate and form an ionic bond through the process of electrostatic attraction. 

  • A stable octet configuration is seen in both the atoms in a molecule of MgO.  

What is the Stability of Atoms? 

If the forces of electrons and protons are balanced, then it is called the stability of atoms. If the electrons in the outermost shell are filled completely or partially then it is regarded as stable, while if it filled less than half then the atom is unstable. Nobles gases along with elements following the octet rule are stable. 


Did You Know?

What does an octet of an electron formation do? It can gain, lose or share electrons with other elements in the outermost shell to form an octet. While valence of electrons shows the total number of electrons present in the outermost shell which can be shared with other elements to form a chemical bond.  

FAQ (Frequently Asked Questions)

Q1. What are the Exceptions to Octet Rule List?

Ans: There are many compounds and elements that don’t follow the octet rule. There are major three exceptions to the octet rule listed below. 

  • An ion, atom, or a molecule that contains an unpaired valence in its outermost or valence shell is called a free radical. These electrons are unstable and they tend to disobey the octet rule. 

  • Elements like hydrogen, helium and lithium don’t obey the octet rule as the first can only accommodate two electrons. Instead, they follow the duet rule. For example, lithium can lose a single electron to hold only two electrons in the valence shell. 

  • Another category to be added in the octet rule and exceptions are the transition elements. Due to the presence of d-orbital they can hold 18 electrons in the exterior shell. 

Q2. What is the Expanded Octet – Hypervalency?

Ans: There are a certain group of elements that have the capacity to form hypervalent compounds. The examples are phosphorus pentachloride (PCl₅) and sulfur hexafluoride (SF₆). If all the bonds in phosphorus-chlorine bonds are covalent, this indicates that phosphorus molecules are not following the octet rule as it is containing ten valence electrons. This five bond configuration of phosphorus molecules is described by the sp3d hybridization in PCl₅. It shows that one s-orbital, one d-orbital and three p-orbital goes through hybridization to form sp3d hybrid. This hybrid orbital creates five covalent bonds with the five chlorine atoms. The final structure we notice is the trigonal bipyramidal in the hypervalent PCl₅ molecule. 

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