centralatom

Central atom

The central atom is the atom at the center of a molecule or ion around which other atoms are arranged. In covalent compounds, it is typically the atom that forms the most bonds and helps determine the molecular geometry, as described by VSEPR theory. In many simple molecules the central atom is the least electronegative element other than hydrogen, though there are notable exceptions.

Identifying the central atom involves considering bond formation and structural constraints. The central atom is usually capable of forming more than one bond and is commonly the element with the greatest bonding capacity among the non-hydrogen atoms in the molecule. Hydrogen is rarely the central atom in neutral compounds. In larger molecules with several potential centers, the choice of a central atom can depend on the expected geometry and the overall connectivity of the structure.

Examples illustrate common patterns. In methane, CH4, carbon is the central atom with sp3 hybridization, yielding a tetrahedral geometry. In ammonia, NH3, nitrogen is central and adopts a trigonal pyramidal arrangement due to one lone pair. In sulfur hexafluoride, SF6, sulfur is central with an octahedral geometry. Water, H2O, has oxygen as the central atom in the sense that it is the atom bonded to both hydrogens, giving a bent geometry due to lone pairs.

In coordination chemistry, the central atom is the metal center around which ligands bind. The electronic configuration and ligand field influence the coordination number and geometry (for example, octahedral Fe(CN)6^4− or [Cu(H2O)6]^2+ as common motifs). The concept of a central atom helps explain molecular shape, reactivity, and physical properties across inorganic and organic chemistry.