Class 12 Chemistry Coordination Compounds Terminology involved

Terminology involved

central metal atom:

  • it is the acceptor metal atom present in the coordination compound
  • It is mostly d block element
  • It act as an acceptor as it has vacant d orbital
  • Due to accepting nature they act as Lewis acids

For example in complex: {Co(NH3)6}Clin this Co is central metal atom



  • They are donor atom may be single atom or group of atoms
  • They are negatively charged or neutral species with lone pair Br-,Cl- etc or neutral like NH3,NO,CO etc
  • They act as Lewis bases
  • We can also call ligands as nucleophile as they are nucleus loving

For example in complex: {Co(NH3)6}Clin this NH3 is ligand



 coordination sphere:

  • It is the combination of atom and ligands.

Example:  in [ Co (NH3)6 Cl3 ]

[ Co (NH3)6 ] is coordination entity or complex

  • They are written in square brackets [coordination entity]
  • This coordination sphere may be positively changed, negatively charged
  • If it is positively charged than it is called as cationic entity and in case of negative charge it is anionic entity or complex.

Example: [Co(NH3)6]3+ cationic entity [Ag (CN)6]- anionic entity

counter ion:

  • The atom or group of atoms written outside bracket is called counter ion.

Example: in [Co(NH3)6].Cl3

Cl3 is a counter ion or the ionizable part when dissolved in water

  • If coordination sphere is with positive charge than counter ion is with negative charge or vice versa.

                 Coordination entity

  • The central metal atom and ligands attached to it forms coordination entity and is written within square brackets

Example :in [Co(NH3)6].Cl3

In this in [Co(NH3)6] is coordination entity

Nature of ligands: Their nature is determined by the property denticity

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