What is Werner's coordination theory?
My coordination theory redefined how we understand complex compounds. I argued that every metal atom has a primary valence—the number of ionic bonds it forms, which satisfies its charge—and a secondary valence, or coordination number, which determines how many atoms or groups directly attach to it in space. For example, in [Co(NH₃)₆]Cl₃, cobalt has a primary valence of 3 (balanced by three chloride ions) and a secondary valence of 6 (occupied by six ammonia ligands). The key is that these ligands are not randomly placed; they adopt specific geometries—octahedral for coordination number 6, tetrahedral for 4, square planar for 4 in some cases. This spatial arrangement explains isomerism: compounds with the same formula but different properties, like the violet and green isomers of [Co(NH₃)₅Cl]Cl₂. Isomerism is the fingerprint of structure. My theory replaced vague ideas of 'molecular compounds' with a precise, three-dimensional model.
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