Now complex ions are ions that are complex,
because they are made up of a number of atoms!
Internally, the complex’s ion atoms are linked up by covalent bonds,
and externally, the whole thing has a charge!
Take hydroxide ion for example…
The O and the H atom are bonded by a covalent bond while externally, the whole hydroxide ion has a -1 charge.
Next up, ammonium ion consists of 4 hydrogen atoms covalently bonded to central atom nitrogen and the whole compound has a charge of +1.
Why do these covalent compounds have charges?
Because complex ions either gained or lost an electron elsewhere.
Examining the electronic configuration below,
For hydroxide ion,
Oxygen atom is stable because it has 8 electrons in its outer shell. H got 2 electrons (1 from sharing) in its shell so it is stable too.
THE key thing to note is O has an electron from elsewhere (the red electron).
For Ammonium ion,
Nitrogen has 8 electrons around its outer shell (5 of its own one, 3 blue ones from hydrogen) and the 4 hydrogen atoms all have stable configuration with 2 electrons in their outer shell but the overall charge stems from the top Hydrogen being a H+.
The H+ has lost an electron (it gets both its electron from Nitrogen) and so the + charge from its electron loss is reflected on the overall.
let look at how these 2 complex ions are formed:
This is a reaction between ammonia and water molecules, both uncharged.
The oxygen from water keeps the shared electron when water releases a H+
The H+ joins nitrogen because nitrogen welcomes it with 2 electrons to stabilise H+
So we get 2 charged complex ions as a result