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Chemsitry!!!

How do you draw the dot and cross diagrams/ lewis structures for polyatomic ions like a carbonate ion and a ammonium ion and a nitrate ion, and how would you know where the dative coordinate bonds are and which element has lost or gained an electron? Thank you

Reply 1

Lilith2400

Original post by Laraib Chaudhry

I've never done this before but I'm pretty sure I know how to work it out from thinking about what group the atoms are in,their lone pairs and types of bonds etc.

Ammonium ion :
The ammonium ion is based off of ammonia which has the chemical formula NH3. Nitrogen is the central atom to the compound and it has 5 electrons in its outter shell. Therefore 3 electrons will be used to form covalent bonds with the 3 H atoms and 2 electrons will be left over to form a lone pair. The presence of a lone pair means a dative bond can form. A hydrogen ion (H+) forms a dative bond with this lone pair which adds a + to the charge of the ion as H+ ions are simply protons and protons have a positive charge. Hence NH4+

Carbonate ion :
Carbon is the central atom of this ion. Carbon can form 4 covalent bonds due to having 4 electrons in its outter shell so as it is bonded to 3 oxygen atoms and has a charge of 2- we can assume one oxygen is bonded via a double covalent bond and two of the oxygens are bonded with single bonds. This is because when oxygen and carbon bond a double covalent bond always forms , therefore having a single covalent bond between an oxygen and carbon atom results in a 1- charge on the oxyen. So fromm the 2- charge I know there are 2 carbon oxygen single bonds and 1 carbon oxygen double bond. This makes sense as 1 double bond and 2 single bonds require 4 electrons from the carbon and carbon has 4 electrons in its outter shell.

Nitrate ion :
Nitrogen is the central atom and has 5 electrons in its outter shell. As it has a 1- charge we can assume there is one nitrogen oxygen single bond and 2 nitrogen oxygen double bonds. This makes sense as 2 double bonds and 1 single bond require 5 electrons from the nitrogen and nitrogen has 5 electrons in its outter shell.

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