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−? An AsO4^3− is polar or nonpolar?
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−?
An AsO4^3− is polar or nonpolar?
The Correct Answer and Explanation is :
Lewis Structure of AsO₄³⁻
To draw the Lewis structure of AsO₄³⁻ (arsenate ion), follow these steps:
- Determine the total number of valence electrons:
- Arsenic (As) has 5 valence electrons.
- Each oxygen (O) atom has 6 valence electrons, and there are 4 oxygens.
- The ion has a -3 charge, which means there are 3 additional electrons. Total electrons = (5 from As) + (4 × 6 from O) + 3 (for the -3 charge) = 29 electrons.
- Structure setup: Place As in the center because it is the least electronegative element (except for hydrogen), and arrange the 4 oxygens around it.
- Distribute the electrons: Form single bonds between As and each O, which uses 8 electrons (4 single bonds). Distribute the remaining 21 electrons as lone pairs on the oxygens.
- Make the structure stable: Oxygen atoms need to satisfy the octet rule, so some of the oxygen atoms will form double bonds with As to complete their octets. The final structure has three oxygen atoms with double bonds to As and one oxygen with a single bond, carrying the negative charge.
The final Lewis structure looks like this:
O
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O = As = O
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O⁻Where the negative charge is on the single-bonded oxygen.
Molecular Geometry of AsO₄³⁻
The geometry of AsO₄³⁻ is tetrahedral. This is because the arsenic atom forms four bonds (three double bonds and one single bond) with oxygen atoms, which results in a symmetrical arrangement of these bonds.
Hybridization of the Central As Atom
The hybridization of the central arsenic (As) atom in AsO₄³⁻ is sp³. This is because arsenic has four regions of electron density around it (four bonds, one single and three doubles).
Approximate Bond Angles
In a tetrahedral geometry, the bond angles are approximately 109.5°.
Polar or Nonpolar?
AsO₄³⁻ is nonpolar. Despite the presence of a negative charge on one of the oxygens, the molecule has a symmetrical tetrahedral geometry, which means the individual bond dipoles cancel each other out, making the overall molecule nonpolar.
Explanation
The key factors influencing the polarity and geometry of AsO₄³⁻ include:
- The tetrahedral molecular geometry, which is determined by the sp³ hybridization of arsenic.
- The electron distribution, where the central atom is surrounded symmetrically by oxygen atoms. While there are formal charges (one oxygen carries a -1 charge), the symmetry ensures that the dipoles cancel out.
- The bond angles of 109.5° result from the repulsion between electron pairs around the central atom, which in turn dictates the tetrahedral shape.
This combination of factors leads to a molecule that is geometrically symmetrical and nonpolar overall.