Shapes of Molecules

• Two bonding pairs of electrons or two double bond pairs
• Linear shape
• Bond angle 180^o

    or    

• Two bond pairs, one lone pair of electrons 
• BENT or V shape
• Bond angle approximately 120^o

•  or 
• 3 electron bond pairs
• TRIGONAL PLANAR:
• Q-X-Q bond angle exactly 120^o: 
• e.g. X = B and Q = H for gaseous boron hydride BH₃

• Two bond pairs and two lone pairs of Electrons
• BENT shape
• e.g. hydrogen sulphide, H2S, or water H2O, 
• i.e. H2X with H-X-H bond angle of approximately 109o (actually 104.5o in water) 
• lone pair-lone pair > lone pair-bond pair > bond pair-bond pair.

•  or 
• Three bond pairs and one lone pair of electrons 
• PYRAMIDAL or TRIGONAL PYRAMID shape
•  e.g. ammonia NH₃ with bond angle of approximately 109^o. 
• Why isn't the H-N-H angle 109^o? The exact H-N-H angle is 107^o due to the extra repulsion of one lone pair.

 or 

• 4 bond pairs of electrons
• TETRAHEDRAL shape
• e.g. methane CH₄, silicon hydride SiH₄ with H-X-H bond angle of 109^o and similarly ions like the ammonium ion NH₄⁺.
• No lone pair, no extra repulsion, no reduction in angle, therefore perfect tetrahedral angle (for H-X-H angles:  CH₄ > NH₃ > H₂O, see below).

 or 

• 5 bond pairs of electrons
• TRIGONAL BIPYRAMID shape
• e.g. phosphorus(V) fluoride (phosphorus pentafluoride) PF₅, gaseous phosphorus(V) chloride, PCl₅
• Bond angles 90^o and 180^o based on the vertical Q-X-Q bond and 120^o based on the central trigonal planar arrangement.

 or 

• 6 bond pairs of electrons
• OCTAHEDRAL SHAPE 
• e.g. sulfur(VI) fluoride (sulphur hexafluoride molecule) SF₆ or the [PCl₆]^- ion and many transition metal complexes
• Q-X-Q bond angles of 90^o and 180^o.(Q TO Q)