paucity (n.) late 14c., from Old French paucitÃ© (14c.) and directly from Latin paucitatem (nominative paucitas) fewness, scarcity, a small number, from paucus few, little, from PIE *pau-ko-, suffixed form of root *pau-(1) few, little (source also of few (adj.)).
All three molecules have four pairs of electrons around their central atom. As a result, they all have a tetrahedral arrangment of electron pairs around the central atom. The bond angle in methane, CH4, is the tetrahedral angle, i.e. 109.5 (109 28'). Ammonia, NH3, contains a lone pair of electrons, which repels the bonding electrons to give a bond angle of 107. The atoms have a trigonal pyramidal arrangement.
1 Trigonal Pyramidal Trigonal pyramidal geometry is also exhibited by molecules having four atoms; one central atom and three peripheral atoms. 2  The central atom in a trigonal pyramidal is at the apex, whereas the other three atoms are at the base, with a bond angle of about 107 degrees.n a trigonal planar, only bond-bond repulsion determines the geometry of the molecule, while in the case of trigonal pyramidal, bond-bond as well as bond-lone pair repulsion is involved in the determination of the geometry of a molecule.