VSEPR and Molecular Polarity

Valence shell electron-pair repulsion theory (VSEPR theory) is a framework that lets us predict bond geometries around central atoms in molecules. As noted by the name, it only considers the electron-electron repulsion found between valence electrons in and between atoms.

Every interaction between atoms in a molecule is a direct result of the electromagnetic forces at play between atoms and valence electrons. VSEPR takes those interactions and predicts the shapes that certain arrangements of atoms and bonding and lone electrons make such that the electron-electron repulsions are minimized and the electron-nuclei attractions are maximized. These arrangements are known as bond geometries and also have associated bond angles that help optimize the molecules even more.

Above is a table that describes the shapes that molecules take around their central atoms given the number of electron regions and lone pairs on the central atoms. Note that double and triple bonds only count as 1 electron region.

Molecular Polarity

Remember that covalent bonds arise when an atomic nucleus attracts another atom's valence electrons. If the two atoms have differing electronegativities, then one of the atoms in the bond will have a slightly positive charge while the other will have a slightly negative charge. This separation of charge is known as a dipole moment. Dipoles are when molecules have two ends, a positively charged end and a negatively charged end. Polar molecules have high dipole moments.