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How do you determine the molecular geometry of a molecule?
The molecular geometry of a molecule can be determined using the VSEPR theory. VSEPR (Valence Shell Electron Pair Repulsion) Theory: The basic premise of this simple theory is that electron pairs (bonding and nonbonding) repel one another; so the electron pairs will adopt a geometry about an atom that minimizes these repulsions. Use the method below to determine the molecular geometry about an atom. Write the Lewis dot structure for the molecule. Count the number of things (atoms, groups of atoms, and lone pairs of electrons) that are directly attached to the central atom (the atom of interest) to determine the overall (electronic) geometry of the molecule. Now ignore the lone pairs of electrons to get the molecular geometry of the molecule. The molecular geometry describes the arrangement of the atoms only and not the lone pairs of electrons. If there are no lone pairs in the molecule, then the overall geometry and the molecular geometry are the same. If the overall geometry is tetrahedral, then there are three possibilities for the molecular geometry; if it is trigonal planar, there are two possibilities; and if it is linear, the molecular geometry must also be linear. The diagram below illustrates the relationship between overall (electronic) and molecular geometries. To view the geometry in greater detail, simply click on that geometry in the graphic below. Although there are many, many different geometries that molecules adopt, we are only concerned with the five shown below.
Why is the molecular geometry of PH3 trigonal pyramidal?
In having three hydrogens attached to a phosphorous atom the arrangement is forced as the lone pairs must be kept as far from each other as possible, thus the geometry here.
What is the electron-pair geometry for SeOF2?
SeOF2 is known as Selenyl Difluoride. The Se atom has one pair of electrons, each F atom has three pairs, and the O has two pairs of electrons.
Which one of the following describes the molecular geometry of a molecule with four electron groups with only bonded pairs?
tetrahedral, if it had three electron groups it would be trigonal planar
What is the molecular geometry of PF3?
In a molecule of phosphorus fluoride, the phosphorus atom is in the center, and it is surrounded by the three fluoride atoms which are arranged at three of the four points of a tetrahedron. (The fourth point of the tetrahedron contains an electron pair from the phosphorus atom.)
