Draw the lewis structure for [SeF5]-, showing the formal charge on each atom. mention the electron and molecular geometry, bond angles, and polarity

Draw the lewis structure for [SeF5]-, showing the formal charge on each atom. mention the electron and molecular geometry, bond angles, and polarity

The Correct Answer and Explanation is:

Lewis Structure for [SeF5]⁻:

1. Step 1: Count the valence electrons
   • Selenium (Se) is in group 16, so it has 6 valence electrons.
   • Each fluorine (F) atom is in group 17, so it contributes 7 valence electrons.
   • The negative charge (⁻) means we add 1 extra electron.
   Total valence electrons:
   • Se = 6
   • 5 F atoms = 5 * 7 = 35
   • 1 extra electron for the charge = 1
   • Total = 6 + 35 + 1 = 42 electrons.
2. Step 2: Draw the skeleton structure
   • Place Se in the center and arrange the 5 F atoms around it. Each F atom forms a single bond with Se.
3. Step 3: Distribute electrons
   • Initially, 5 bonds use 10 electrons (2 electrons per bond).
   • Distribute the remaining 32 electrons as lone pairs on the fluorine atoms. Each fluorine gets 6 electrons (3 lone pairs).
   • After assigning the lone pairs to fluorines, we are left with no electrons for the selenium atom, so we put the remaining electrons on Se.
4. Step 4: Check for octet rule
   • Selenium can expand its octet because it is in period 4, so it can hold more than 8 electrons.
   • The structure satisfies the octet for all fluorine atoms, and Se has 10 electrons in its valence shell.
5. Step 5: Formal charge calculation
   • Formal charge formula: Formal Charge = (Valence electrons) – (Lone pair electrons + 1/2 Bonding electrons)
   • Se (Selenium):
     • Valence electrons = 6
     • Lone pair electrons = 0
     • Bonding electrons = 10 (from 5 bonds)
     • Formal charge = 6 – (0 + 10/2) = 6 – 5 = +1
   • F (Fluorine):
     • Valence electrons = 7
     • Lone pair electrons = 6 (3 lone pairs)
     • Bonding electrons = 2 (1 bond with Se)
     • Formal charge = 7 – (6 + 2/2) = 7 – 7 = 0
   So, the formal charge on Se is +1, and each F atom has a formal charge of 0.

Molecular Geometry:

• The molecular geometry of [SeF5]⁻ is trigonal bipyramidal.
  • This is due to the 5 bonding pairs around the central Se atom.

Electron Geometry:

• The electron geometry is also trigonal bipyramidal, as there are 5 bonding pairs and no lone pairs on Se.

Bond Angles:

• In a trigonal bipyramidal structure, the bond angles are:
  • 90° and 120° between equatorial and axial positions.
  • 120° between the equatorial positions.

Polarity:

• Polarity: The molecule is polar. Although the individual F-Se bonds are polar, the geometry is asymmetrical (due to the presence of the negative charge), leading to an overall dipole moment.