Duplet and Octet Rules| Definition, Concept Points, Examples|

 All atoms are unstable alone- except monoatomic molecules (noble gases) are stable atoms- atoms want to be stable by making molecules. In process of making molecules atoms follow either duplet or octet rules. Actually all atoms tend to be like its nearest noble gas by copying their electronic configurations. All noble gases have eight electronic configuration i.e  noble gases have eight electrons in valence shell except helium( He) which has 2 electrons in valence shell. in order to get electronic of its nearest noble gas atoms either get electrons, lose electrons or share electrons. then they form stable molecules and compounds.

OCTET RULE:

An atom tends to get electronic configuration of its nearest noble gas- in order to get stable like noble gases- in periodic table by having 8 electrons in its valance shell.

EXAMPLES:

Sodium ( Na) belongs to IA group in periodic table.its atomic number (Z) is 11. IA group elements have 1 electron in its outer most shell.Group number represents the number of electrons in outer most shell. According to octet rule each element tries to get electronic configuration of its nearest noble gas in periodic table. In periodic table the nearest noble gas to Na( Z=11) is Ne ( Z=10) having atomic number 10. 

Electronic configuration of NEON (Ne) is: ₁₀Ne = 1s^2, 2s^2, 2p⁶    

Electronic configuration of SODIUM (Na)  is: ₁₁Na = 1s^2, 2s^2, 2p⁶,3s¹ 

In order to get the stability Na atom loses one electron  and gets eight electronic configuration like Ne. here is sodium is following octet rule by losing 1 electron and getting stable.look carefully Na+1 has electronic configuration just like Ne.

₁₁Na = 1s^2, 2s^2, 2p⁶,3s¹     → Na⁺¹ = 1s^2, 2s^2, 2p⁶  + 1e^-

Take another example , Chlorine has 17 atomic number (Z ) .

Chlorine ( Cl) belongs to VIIA group in periodic table. its atomic number is 17. VIIA group elements have 7 electrons in its outer most shell. Group number represents the number of electrons in outer most shell. According to octet rule each element tries to get electronic configuration of its nearest noble gas in periodic table. In periodic table the nearest noble gas to Cl (Z=17) is argon (Ar = 18)). Ar is  having atomic number  Z=18. 

Electronic configuration of ARGON (Ar) is: ₁₈Ar = 1s^2, 2s^2, 2p⁶,3s^2,3p⁶

 Electronic configuration of CHLORINE (Cl)  is: ₁₇Cl = 1s^2, 2s^2, 2p⁶,3s^2,3p⁵

 

In order to get the stability Cl atom gains one electron  and gets eight electronic configuration like Ar. Here is Cl is following octet rule by gaining 1 electron and getting stable.carefully look at the electronic configuration of Cl-1 which is just like Ar.

₁₇ Cl = 1s^2, 2s^2, 2p⁶,3s^2, 3p⁵   + 1e^-   → Cl^-1 = 1s^2, 2s^2, 2p⁶,3s^2, 3p⁶  

 

 NOTE POINT: After following the octet rule Na is forming Na+1 and Cl-1 due to these charges they get bonded with each other form sodium chloride NaCl ionic compound  and compound is a stable chemical species.

DUPLET RULE:
An atom tends to get electronic configuration of its nearest noble gas HELIUM - in order to get stable like HELIUM- in periodic table by having 2 electrons in its valance shell.

EXAMPLES :

Lithium ( Li) belongs to IA group in periodic table.its atomic number (Z) is 3. IA group elements have 1 electron in its outer most shell.Group number represents the number of electrons in outer most shell. According to duplett rule each element tries to get electronic configuration of helium gas. 

Electronic configuration of HELIUM (He) is: ₂He = 1s²    

Electronic configuration of LITHIUM (LI)  is: ₃LI = 1s^2, 2s¹

In order to get the stability Li atom loses one electron  and gets 2 electronic configuration like He. here is lithium is following duplet rule by losing 1 electron and getting stable. carefully look Li+1 has electronic configuration just like He.

₃ Li = 1s^2, 2s¹     → ₃ Li⁺¹ = 1s² + 1e^-