Knowra Trigonal pyramidal molecular geometry Trigonal pyramidal molecular geometry A molecular shape in which a central atom is bonded to three atoms, while a lone electron pair occupies the fourth position of a tetrahedral arrangement.
Valence shell electron pair repulsion theory : A model that predicts molecular shapes by treating regions of valence-electron density as mutually repulsive. It predicts a tetrahedral electron-domain arrangement when the central atom has three bonds and one lone pair.
Bond angle : The angle between two bonds that share an atom. The H–N–H angle in ammonia is about 107 degrees, below the tetrahedral angle.
Phosphine : A molecule with formula PH₃, with a phosphorus atom bonded to three hydrogen atoms. It has trigonal pyramidal geometry, but its bond angles differ markedly from ammonia’s.
Trigonal planar molecular geometry : A molecular shape with a central atom bonded to three atoms in one plane, with no lone pair in the arrangement. It has three bonded atoms like the pyramidal shape, but no fourth electron domain.
Electron domain : A region of electron density around an atom, such as a bond or a lone pair. The geometry counts the central atom’s three bonding domains and one lone-pair domain.
Ammonia : A molecule with formula NH₃, consisting of a nitrogen atom bonded to three hydrogen atoms. Its nitrogen lone pair makes ammonia the standard example of this geometry.
Chloramine : A molecule with formula NH₂Cl, in which nitrogen is bonded to two hydrogen atoms and one chlorine atom. Its nitrogen center is trigonal pyramidal, with unequal substituents affecting its properties.
Seesaw molecular geometry : A molecular shape with four bonded atoms and one lone pair around a central atom in a trigonal-bipyramidal electron arrangement. It also has a lone pair, but five electron domains rather than four.
Lone pair : A pair of valence electrons localized on one atom and not shared in a covalent bond. Its greater repulsion relative to bonding pairs helps compress the bond angles.
Repulsion between electron pairs : The electrostatic interaction that causes regions of electron density around an atom to spread apart. The lone pair exerts stronger repulsion than bonding pairs and narrows the bond angles.
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