Answer:
Si; none; 109.5°; the same
Explanation:
1. Central atom
The formula for the orthosilicate ion is SiO₄⁴⁻.
The central atom is the atom with the smaller electronegativity.
Electronegativities are: Si = 1.90; O = 3.44.
Si is less electronegative, so Si is the central atom.
2. Draw an electron-dot structure
(a) Count the valence electrons
1 × Si (Group 14) = 4
4 × O (Group 16) = 4 × 6 = 24
+4 e⁻ (for the charges) = 4
Total = 32
(b) Draw a trial structure
Put Si in the middle with four bonds to O.
Give every atom an octet.
(c) Count the valence electrons
Valence electrons = bonding pairs + lone pairs
VE = BP + LP = 4BP + 12LP =8 + 24 = 32 electrons
The number of electrons in the structure equals the number of electrons available.
The trial structure is correct.
The central atom (Si) has no lone pairs.
3. Theoretical bond angles
A molecule with four bonding pairs and no lone pairs about the central atom has a tetrahedral shape. The ideal bond angles are 109.5°.
4. Actual Bond Angles
The orthosilicate ion has tetrahedral symmetry.
The actual bond angle should be the same as the ideal bond angle (109.5°).
