About Molecular Geometry
Molecular geometry describes the three-dimensional arrangement, or shape, of the atoms within a molecule. The shape is determined by the repulsion of the bonded and lone pair electrons surrounding the central atom. The molecular geometry dictates the physical and chemical properties of the molecule.
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Linear
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Molecules with two bonded pairs of electrons and no lone pair electrons have a bond angle of 180 degrees. This arrangement is described as linear. This arrangement also occurs if there are three lone pairs of electrons in addition to the two bonded pairs around the central atom. Carbon dioxide (CO2) is an example of a linear molecule.
Trigonal Planar
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Three bonded pairs of electrons with no lone pairs of electrons produce a trigonal planar-shaped molecule. The 120-degree bond angle produces a flat-shaped molecule arranged with three atoms at the points of a triangle around the central atom. This shape is found in formaldehyde (H2CO).
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Bent
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When two bonded pairs of electrons accompanied by either one or two lone pairs of electrons around the central atom, then the molecular geometry is described as bent. The angle of the bend varies with the number of lone pair electrons. This is the shape found in nitrogen dioxide (NO2) and water (H2O).
Tetrahedral
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Four bonded pairs of electrons without any lone pairs of electrons around the central atom create a molecular shape where each of the bonded atoms lays at the point of a tetrahedron. Methane (CH4) is an example of a tetrahedral molecule.
Other Shapes
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Additional shapes include trigonal pyramidal, trigonal bipyramidal, seesaw, T-shaped, octahedral, square pyramidal, and square planar, each depending on the number of bonded and lone electron pairs.
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