Introduction to complex salts

 Hello fam! Welcome to today’s lesson. We would focus our study today on trying to understand what we mean by a complex salt. I advise that you look at the lessons on June 18 and July 6, 2023 found on the page timeline for a detailed explanation of the idea of the coordinate bond.


I will try to give a little introduction here but looking at the lessons I quoted above are indispensable to making the most out of this lesson. 


A coordinate bond is formed when ONLY ONE of the bonding species supply the electron pair that is shared in the covalent bond. In other words, a coordinate bond must involve a  Lewis acid (electron pair acceptor) and a Lewis base, (electron pair donor).


Let us look at a typical example. Consider the formation of [Cu(NH3)4]Cl2. Remember that the ground state electron configuration of the copper II ion is written as; [Ar]3d9 4s0. 


This implies that we have empty 4s and 4p orbitals that can participate in dsp2 hybridization (forming a square planar complex) along with one of the five 3d orbitals. Given that the 3d orbitals in copper II ion are almost completely filled, the only unpaired electron in the 3d sublevel is promoted to the 4pz level making one 3d, one 4s and two 4p orbitals available for hybridization. This is how the dsp2 hybridization in the complex occurs.


So what exactly is happening here? Four lone pairs from nitrogen central atoms in four ammonia molecules are donated into four empty hybrid dsp2 orbitals on the copper II central metal ion to form the complex ion that can be written as [Cu(NH3)4]^2+. The two chloride ions are called counter ions and they serve to balance the charges.


Do you recall that I told you that a salt is formed anytime another cation replaces hydrogen in an acid? The cation may be a simple metal ion, ammonium ion or a complex cation such as what we have here as [Cu(NH3)4]^2+. When the cation in the salt is a complex cation then we have a COMPLEX SALT.


Tomorrow, I will go deeper to explain the nature of bonding in the cation, [Cu(NH3)4]^2+. You definitely do not want to miss tomorrow’s lesson. 


Do you remember that I told you yesterday that one of the differences between a complex salt and a double salt is that a double salt yields simple ions in solution while a complex salt does not yield simple ions in solution? I will talk more about that point tomorrow. See you then!


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