Coordination Bonds and Complex Ions
What Are Coordination Bonds?
Definition
Coordination bond
A coordination bond (also known as a dative covalent bond) forms when both electrons in the shared pair come from the same atom.
In the context of complex ions, this occurs when a ligand donates a lone pair of electrons to a transition metal cation.
Definition
Ligand
A molecule or ion that donates a lone pair of electrons to a central metal ion to form a coordination bond.
Common ligands include water ($H_2O$), ammonia ($NH_3$), and chloride ions ($Cl^-$).
Other important definitions:
- Transition Metal Cation: A positively charged ion of a transition metal, which has vacant orbitals capable of accepting electron pairs from ligands.
- Complex Ion: A charged species consisting of a central metal ion surrounded by ligands bonded through coordination bonds.
Ligands must have at least one lone pair of electrons to form a coordination bond with the metal ion.
How Are Coordination Bonds Formed?
- Coordination bonds are formed when ligands donate their lone pairs of electrons to the empty orbitals of a transition metal cation.
- This process can be broken down into the following steps:
- Electron Pair Donation: The ligand, which has a lone pair of electrons, approaches the transition metal cation.
- Orbital Overlap: The lone pair of electrons from the ligand overlaps with an empty orbital on the metal ion.
- Bond Formation: A coordination bond is established, resulting in the formation of a complex ion.
Why Transition Metals?
Transition metals are particularly suited to forming complex ions because:
- They have vacant d-orbitals that can accept electron pairs.
- Their high charge density attracts electron-rich ligands.
