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.
PH3 molecule has the central atom of phosphorus connected by single bonds to three hydrogen atoms.The phosphorus atom also has one pair of unshared electrons.The electron-cloud geometry of the phosphorus atom is tetrahedral, but the molecular geometry of phosphorus trihydride is trigonal pyramidal, when the nuclei of the three hydrogen atoms are each connected to the nucleus of the phosphorus atom.est Answer: Bent-only works with two substituents. Linear works with one. Tetrahedral only works with four, so you're left with trigonal planar and trigonal pyramidal. Look what you know about P: it has 5 electrons, but in PH3 it is only using three, so the odd pair have to go somewhere.