Notes on Electron Density and Molecular Geometry

Electron Geometry: Tetrahedral
Molecular Geometry: Tetrahedral - In methane, carbon is the central atom bonded to four hydrogen atoms. This arrangement leads to a symmetrical molecular shape with no lone pairs affecting the geometry.
Bond Angles: 109.5 degrees - These angles are a result of the tetrahedral arrangement, optimizing the distance between the electron pairs.
Polarity: Non-polar - As the molecule has identical peripheral atoms (hydrogens), the symmetrically distributed charge leads to no net dipole moment.
- If one hydrogen is replaced with a different atom, such as fluorine, the molecule becomes polar due to the resulting asymmetrical charge distribution, leading to a net dipole.

Electron Geometry: Tetrahedral
Molecular Geometry: Trigonal Pyramidal - Ammonia features one lone pair and three hydrogen atoms bonded to the nitrogen atom. The presence of the lone pair reduces the bond angle slightly due to repulsion, altering the molecular shape from tetrahedral to trigonal pyramidal.
Bond Angles: Slightly less than 109.5 degrees - This reduction in bond angle is primarily caused by the stronger repulsive forces exerted by the lone pair.
Polarity: Polar - The lone pair's presence creates an asymmetrical distribution of charge, resulting in a net dipole moment that gives ammonia its polar characteristics. This polarity plays a critical role in ammonia's solubility in water and its reactivity in various chemical processes.

Electron Geometry: Tetrahedral
Molecular Geometry: Bent/Angular - Water has two lone pairs and two hydrogen atoms bonded to the central oxygen atom. The two lone pairs exert greater repulsion on the bonded pairs, leading to a bent molecular shape rather than a linear one.
Bond Angles: 104.5 degrees - The bond angle is decreased from the ideal tetrahedral angle due to the increased repulsion between the lone pairs compared to the bonded pairs.
Polarity: Polar - The bent shape and the high electronegativity of oxygen create an asymmetrical distribution of electrons, resulting in a net dipole moment. This polarity is crucial for water's unique properties, including its solvent capabilities and high surface tension.

Electron Geometry: Trigonal Bipyramidal - In PF₅, phosphorus is the central atom surrounded by five fluorine atoms. The arrangement positions three of the fluorines in equatorial positions and two in axial positions, minimizing electron repulsion and stabilizing the molecule.
Molecular Geometry: Trigonal Bipyramidal - This geometry remains tetrahedral as there are no lone pairs altering the symmetrical shape around the phosphorus atom.
Bond Angles: 90 degrees (for axial positions), 120 degrees (for equatorial positions), 180 degrees (between axial positions) - These angles highlight the unique geometry of trigonal bipyramidal molecular structures.
Polarity: Non-polar - The identical fluorine atoms surrounding the phosphorus atom lead to a symmetrical molecule, allowing for the cancellation of dipole moments and resulting in a non-polar characterization of PF₅.

Electron Geometry: Trigonal Bipyramidal - The structure of SF₄ involves four fluorine atoms surrounding the sulfur atom, with one lone pair located in the equatorial position.
Molecular Geometry: Seesaw - The presence of the lone pair causes a distortion in the molecular structure from the ideal form of trigonal bipyramidal to a seesaw shape due to lone pair-bonding pair repulsion.
Bond Angles: 90 degrees (for axial bonds), 120 degrees (for equatorial bonds), and 180 degrees (between axial positions) - The angles vary due to the impact of the lone pair's presence.
Polarity: Polar - The seesaw shape creates an asymmetrical charge distribution due to the influence of the lone pairs, leading to a net dipole moment that renders SF₄ polar, impacting its interactions with other substances and its role in various chemical reactions.