CBSE Class 11-science Answered

STEP 1

Find the valence electron configuration of each atom in the molecule. The valence electrons will be placed on the atomic orbital for that atom. Do this for each atom. Ex) Boron (B) = (He)2s² 2p¹ = 3 valence electrons

STEP 2

Decide if the molecule is homonuclear of heteronuclear. If the molecule is homonuclear, the AOs will be symmetric. Heteronuclear AOs will be slightly different because the more electronegative atom will be placed lower on the diagram. This is due to lone pairs of electrons being more stable on more electronegative elements leading them to be lower in energy. Ex) HF = “F” will be placed lower in the diagram than “H”.

STEP 3

Fill molecular orbitals using energy and bonding properties of the overlapping atomic orbitals. Keep in mind the energy of the atomic orbitals and molecular orbitals! The following factors contribute to the position of one MO with respect to other MOs.

• More nodes = more energetic = higher MOs
• Sigma orbitals are stronger than pi bonds
• Antibonding MOs are higher in energy than bonding MOs
• Constructive overlap = fewer nodes = more stable (less energetic)
• Destructive overlap = more nodes = less stable (more energetic)

STEP 4

Use the diagram to predict properties of the molecule. Remember: the number of individual atomic orbitals should equal the number of MOs! Ex) Bond order, bond angle, paramagnetism, etc.