Let’s Shape the Molecules

Why does the molecule shape important?

The molecule is very important in terms of size and shape because each characterizes different function in cells.

VSEPR Model: Use to predict the shapes and angles of the molecule using their “pair electrons that surround the central molecules”

VSEPR for Lewis Structure: Valance electron, Skeleton, Electron, Pairs of bond, Review formal charge

Example: H2O

Valance electron: H2 = 1 x 2 = 2, O = 6, Sum of both valance electron is 8

Skeleton: = 2 electrons or we call it pair bond sharing between the molecule, HOH

Electron: Check it whether each molecule satisfy with their electron, Ex: H has 2 (share with O), which it is satisfying because it has the same outer shell like Helium

Pairs of bond: Check the structure whether it has more than one pair bond to share

Review Formal charge: To check all of the molecules, whether they satisfy their own needs or forget to create other pairs of bond

VSEPR for: Valance-Shell Electron-Pair Repulsion

Two bonded pairs:

Linear: only two bonded pair, 180o, non-polar

Bend: 2 bonded and 1 lone pair/s, <120o, polar

Trigonal planar: if only 3 bonded pairs, 120o, non-polar

Trigonal pyramidal- 3 bonded but also a lone pair, <109.5o, Polar

Tetrahedral: If only 4 bonded pairs, 109.5o, non-polar

See-saw: If 4 bonded and 1 lone pair, <900 and <1200, non-polar

Trigonal bipyramidal: If five bonded pairs, 900 and 1200, non-polar

Octahedral: If six bonded pairs, 900, non-polar

Example: SiS2


  • Lewis Structure
  • Check the lone pair/s electron
  • Identify the shape
  • Add the angle
  • Polar/non-polar


  • There are no lone pairs
  • Linear
  • 1800
  • Non-polar

Resources: https://www.youtube.com/watch?v=xNYiB_2u8J4