Therefore, they tend to have the least amount of interaction with the bonding pairs. They are closer to the central atom’s nucleus and spread over a larger space than bonding electrons. Lone pairs are assumed to have a more significant repulsive effect than bonding pairs. The lone pairs are located in the atomic orbitals of the central atom and repel other orbitals, causing a deviation from the abovementioned geometry.
Nonbonding electrons or lone pairs on the central atom affect the molecular shape. Examples are sulfur hexafluoride (SF 6) and molybdenum hexacarbonyl Mo(CO) 6. Octahedral or square bipyramidal: It describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom such that they are positioned at the vertices of an octahedron. Examples are phosphorous pentachloride (PCl 5) and arsenic pentafluoride (AsF 5).ĥ. The bond angle is 90° in one plane and 120° in another plane. The central atom is surrounded by five atoms – three in one plane and two on opposite sides of the plane. Unlike the trigonal planar, the trigonal bipyramidal structure is three-dimensional. Trigonal Bipyramidal: The molecule’s shape resembles a pyramid with a triangular base. This shape is because the four bond pairs experience minimum repulsion when the bonds are directed toward the corners of the tetrahedron. Tetrahedral: This shape occurs when one atom occupies the center, and four others are located at the corners of a tetrahedron. Examples are boron trifluoride (BF 3), boron trichloride (BCl 3), and sulfur trioxide (SO 3).ģ. It has one atom at the center and three at the corners of an equilateral triangle, making a bond angle of 120°. Trigonal Planar: The molecule forms a triangular shape in one plane. Examples of molecules with linear geometry are carbon dioxide (CO 2), beryllium chloride (BeCl 2), and nitric oxide (NO).Ģ. The atoms are arranged in a straight line, and the angle between the bonds, or bond angle, is 180 °. Linear: It specifies the geometry shaped by a central atom surrounded by two other atoms.
The VSEPR theory describes five main shapes of simple molecules. Shape of Moleculesįirst, we shall consider the molecular shape without lone pairs on the central atom. For example, the water (H 2O) molecule has two bond pairs and two lone pairs. If lone pairs are present, the letter E n is added, where “n” represents the number of lone pairs surrounding the central atom. An electron group consists of a single bond, double bond, or triple bond. “X” represents the surrounding atoms, and “m” is the number of electron groups associated with the central atom. Īccording to VSEPR theory, a molecule is designated by the letters AX m. The angle between the adjacent bonds defines the bond angle. As a result, the molecule forms a regular geometric shape. According to this theory, the lone pairs in the valence shell of the central atom will rearrange themselves in such a way as to minimize the repulsion and maximize the distance between them. It predicts a molecule’s shape based on the number of bonds and lone pairs.
Molecular geometry is generally studied using the VSEPR theory, which is an abbreviation for valence shell electron pair repulsion. Molecular geometry is vital in chemistry to determine a substance’s physical and chemical properties, like color, reactivity, polarity, and state of matter. A molecule consists of a central atom chemically bonded to several side atoms, resulting in a well-defined shape and a finite bond angle. Molecular geometry refers to the arrangement of atoms in a molecule in a two- or three-dimensional structure.
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