Draw the Lewis structure of AsO4^3- showing all lone pairs. Identify the molecular geometry of AsO4^3-. What is the hybridization of the central As atom? What are the approximate bond angles in AsO4^3-? Is AsO4^3- polar or nonpolar? Please answer all parts.
The Correct Answer and Explanation is:
Answer:
- Lewis Structure of AsO₄³⁻:
The central atom is As (arsenic), surrounded by four O (oxygen) atoms. Each O forms a single bond with As. Each oxygen has 3 lone pairs of electrons. The overall ion has a –3 charge, typically distributed as one oxygen atom bearing the full –1 charge (with an extra lone pair), and the other three being neutral due to resonance. - Molecular Geometry:
Tetrahedral - Hybridization of Central As Atom:
sp³ - Approximate Bond Angles:
109.5° - Polarity:
Nonpolar
Explanation
The Lewis structure of AsO₄³⁻ begins with arsenic (As) as the central atom, surrounded by four oxygen atoms. Arsenic has 5 valence electrons, and each oxygen has 6, totaling 29 valence electrons. Adding 3 electrons for the –3 charge gives 32 valence electrons.
Each As–O bond is a single bond, which uses 8 electrons (4 bonds × 2 electrons). The remaining 24 electrons are distributed as lone pairs around the oxygens. Each oxygen gets 6 electrons (3 lone pairs), satisfying their octets. This structure also accommodates the –3 charge, usually delocalized across the four oxygens due to resonance. In reality, this ion exhibits resonance, meaning the negative charge is shared among the oxygen atoms, making all As–O bonds equivalent.
The molecular geometry is tetrahedral, as there are four regions of electron density (four bonded oxygens) around the central arsenic atom and no lone pairs on As. According to VSEPR theory, this leads to a tetrahedral shape to minimize electron repulsion.
The hybridization of arsenic in this tetrahedral structure is sp³, indicating that one s and three p orbitals mix to form four equivalent sp³ orbitals used to bond with the oxygens.
The bond angles in a perfect tetrahedron are approximately 109.5°.
Finally, although AsO₄³⁻ carries an overall charge, its molecular shape is symmetrical. The equal distribution of charge and geometry causes the dipole moments to cancel out, making the ion nonpolar overall, even though individual As–O bonds are polar due to electronegativity differences.
