Describe octahedral, tetrahedral and square planar complexes.

In the subtopic Complex ions and ligand substitution (A-level only), this AQA A-Level Chemistry 7405 learning objective focuses on describe octahedral, tetrahedral and square planar complexes. It belongs to Transition metals (A-level only), so revision should stay anchored to this exact subtopic rather than drifting into a generic GCSE-level chemistry summary. Approved keywords to use include octahedral, tetrahedral, square planar. Tetrahedral complex. means a complex ion with four coordinate bonds arranged around a central metal ion, forming a tetrahedral shape Avoid the mistake of students often confuse the geometry of octahedral and tetrahedral complexes, mistakenly describing tetrahedral complexes as octahedral due to the number of ligands; instead, to fix this, remember that octahedral complexes have six ligands arranged around the central metal ion, while tetrahedral complexes have four ligands. Visualize the shapes: octahedral complexes resemble two pyramids base-to-base, while tetrahedral complexes form a three-dimensional triangle. Always relate the number of ligands to the geometry For exam answers, when predicting the geometry of a transition‑metal complex, first count the total number of valence electrons (metal d‑electrons + ligand electrons). If the sum is 18, the complex is likely to be stable and adopt a common geometry (octahedral for six‑coordinate, tetrahedral for four‑coordinate, square planar for four‑coordinate with d⁸ metal)