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MCAT Chemistry Question — Calcium Electron Configuration

  • by John
  • Aug 04, 2014
  • MCAT Question of the Day

What is the electron configuration of Ca in Ca(OH)2?

 

A) 1s22s22p6

 

B) 1s22s22p63s2

 

C) 1s22s22p63s23p6

 

D) 1s22s22p63s23p64s2

Explanation

Calcium in Ca(OH)2 exists as an ion Ca2+. The electron configuration of Ca2+ is equivalent to Argon, with orbitals up to 3p filled with electrons. Normally, Ca has the configuration of [Ar]4s2. [Ar] is shorthand for 1s22s22p63s23p6. You may see this shorthand for noble gas electron configurations on the MCAT.

 

A) 1s22s22p6, incorrect, This is the configuration for Neon, Na+, and Mg2+.

B) 1s22s22p63s2, incorrect, This is the configuration for Mg.

C) 1s22s22p63s23p6, correct, Ca2+ has lost its 4s1 and 4s2 electrons.

D) 1s22s22p63s23p64s2, incorrect, This is the configuration for Ca, but not Ca2+.

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