COCHRANES OF OXFORD MOLECULAR MODELS - BRIEF INSTRUCTIONS
Plastic balls with prongs for bond connections are used to represent the nuclei (atom centers) of various elements. Straws of various lengths are used to represent bonds.
Type of Atom # of Prongs Bond Angle (deg) Color Shape H 1 - White 
C (sp3) 4 ~ 109.5 Black 
C (sp2) 3 ~ 120 Black 
C (sp1) 2 ~ 180 Black 
O (sp3) 2 ~ 105-112 Red 
O (sp3) - or use a 4-prong tetrahedral center to show lone-pair electrons O (sp2) 1 - Red O (sp2) - or use a 3-prong (120 deg) center to show lone-pair electrons N (sp3) 4 ~ 107-113 Blue N (sp3) (one of the prongs will represent the lone-pair electrons) N (sp2) 3 ~ 120 Blue N (sp2) (two of the prongs will represent lone-pair electrons) Halogens 1 - Green Use straws of various lengths to reprent bonds. Suggested straw lengths for several bond lengths are shown below. For more accurate models, the straws can be cut to scale (3 cm = 0.100 nm is a convenient scale).
To depict multiple bonds, the clear pegs (
C(sp3)-C(sp3) 0.154 nm Longest Straw C(sp3)-H 0.111 nm Shortest Straw C(sp2)-C(sp2) 0.134 nm Medium Straw C(sp2)-H 0.110 nm Shortest Straw C(sp1)-C(sp1) 0.121 nm Medium Straw C(sp1)-H 0.108 nm Shortest Straw ) can be inserted on appropriate atoms to attach extra straws for bonds -- two straws total for double bonds; three for triple bonds.