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Question

Select the molecule in which the central atom has incomplete octet.


A

Beryllium

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B

Phosphorous

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C

Silicon

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D

Chlorine

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Solution

The correct option is A

Beryllium


Explanation for correct answer:-

Option (A) Beryllium

  • Beryllium(Be) has an atomic number of 4, and its electronic configuration is 1s22s2.
  • As we can see from this electronic configuration, we can see that it does not need 8 electrons in its valence shell to achieve the octet state.
  • This is because the outermost shell is s-orbital, which can only accommodate 2 electrons, not 8.
  • Thus Beryllium(Be) along with Lithium(Li), Hydrogen(H), and Helium(He) does not obey this octet rule and hence are incomplete octet.
  • Hence it is the correct option.

Explanation for incorrect answer:-

Option (B) Phosphorus

  • Phosphorus has an atomic number of 15, and its electronic configuration is 1s22s22p63s23p3.
  • As we can see It needs 3 more electrons to complete its octet.
  • As a result it reacts with another Phosphorus atom and they both share the 3 electrons present in the p-orbital and thus complete its octet.
  • Hence it is a complete octet.
  • Hene it is the incorrect option.

11221_Chemistry_62e8f2f6b40b3f0c7f899e7e_EL_Incomplete_Octet-22_034416.jpg

Option (C) Silicon

  • Silicon has an atomic number of 14, and its electronic configuration is 1s22s22p63s23p2.
  • As we can see It needs 4 more electrons to complete its octet.
  • As a result it reacts with another Silicon atom and they both share the 4 electrons present in their valence shell and thus complete its octet.
  • Hence it is a complete octet.
  • Hence it is the incorrect option.

11221_Chemistry_62e8f2f6b40b3f0c7f899e7e_EL_Incomplete_Octet-22_034416_b.jpg

Option (D) Chlorine

  • Chlorine has an atomic number of 17, and its electronic configuration is 1s22s22p63s23p5.
  • As we can see It needs 1 more electron to complete its octet.
  • As a result it reacts with another Chlorine atom and they both share 1 electron from their valence shell and thus complete its octet.
  • Hence it is a complete octet.
  • Hence it is the incorrect option.

11221_Chemistry_62e8f2f6b40b3f0c7f899e7e_EL_Incomplete_Octet-22_034416_c.jpg


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