Determine Coordination Number of Cations in Chemical Equation

[Mitchtwitchita]

Can anybody please tell me if there's a way to determine the coordination number of a cation in relation to an anion just from the chemical equation (without atomic radii, tables, etc.)? For example, the C.N. of Ca2+, Al3+ and Si4+ in Ca3Al2Si3O12 (grossular garnet).

 

[GCT]

I'm pretty certain that you need to know the structure for this one.

 

[Blueshift5]

Yes, there is a way to determine the coordination number of cations in a chemical equation without using atomic radii or tables. This can be done by analyzing the chemical formula of the compound and understanding the bonding patterns between the cations and anions.

In the case of Ca3Al2Si3O12, the chemical formula indicates that there are three Ca2+ ions, two Al3+ ions, and three Si4+ ions present. This implies that each Ca2+ ion is bonded to six O2- ions, each Al3+ ion is bonded to four O2- ions, and each Si4+ ion is bonded to four O2- ions. This results in a coordination number of 6 for Ca2+, 4 for Al3+, and 4 for Si4+.

This can be further confirmed by looking at the electronic configurations of these cations. Ca2+ has a 2+ charge and an electronic configuration of [Ar] 3d^0, indicating that it can form six bonds with O2- ions. Al3+ has a 3+ charge and an electronic configuration of [Ne] 3s^2 3p^1, indicating that it can form four bonds with O2- ions. Si4+ has a 4+ charge and an electronic configuration of [Ne] 3s^2 3p^2, also indicating that it can form four bonds with O2- ions.

Therefore, by analyzing the chemical formula and the electronic configurations of the cations, we can determine the coordination number of Ca2+, Al3+, and Si4+ in Ca3Al2Si3O12 without using atomic radii or tables.