Question

Use the Lewis structure to predict the molecular geometry of each molecule.

mc001-1.jpg

tetrahedral

trigonal planar

trigonal pyramidal

Answer 1

I can’t see the image you attached — could you re-upload it or tell me the molecular formulas/names? Meanwhile, here’s how to decide the geometry from a Lewis structure and the three common results you listed:

Steps (VSEPR method)
1. Draw the Lewis structure (count valence electrons, place bonds, add lone pairs to complete octets).
2. Choose the central atom (usually the least electronegative that isn’t hydrogen).
3. Count electron domains (regions of electron density) around the central atom: each single/double/triple bond counts as one domain, each lone pair counts as one domain.
4. Use the electron-domain number and lone-pair count to assign the molecular shape (arrangement of atoms, ignoring lone pairs).

Common cases you listed
- Tetrahedral: 4 electron domains, 0 lone pairs on central atom (e.g., CH4).
- Trigonal planar: 3 electron domains, 0 lone pairs (e.g., BF3, CO3^2– resonance average).
- Trigonal pyramidal: 4 electron domains, 1 lone pair on central atom (e.g., NH3).

If you send the picture or the formulas, I’ll identify each molecule’s geometry specifically.