What is the VSEPR theory?

(The answer really depends on the level of the student, hence more or less explanation might be needed.)The VSEPR (Valence Shell Electron Pair Repulsion) theory is used within chemistry to predict the geometric shape of molecules. As electrons are all negative, each electron tries to push other electrons away from itself, reaching equilibrium based on the number of electrons present in the outer shell. Therefore, the most standard octahedral molecular arrangement has electrons positioned at 90 degree angles relative to the nucleus [insert drawing]. As the numbers of electrons decrease, the angles increase [more drawings]. However, not all molecules have an atom corresponding to each pair of valence electrons. Those electrons which are not shared with other atoms are known as lone pairs. For instance, a classic example is H2O. H2O has 2 pairs of non-bonding electrons. These two lone pairs repel the bonds and create a difference between the electron skeleton and the molecular shape of the molecule [insert drawing]. This is important to take into account as the molecular shape is important for identifying the chemical and physical properties of the molecule.