An explanation sheet for making
Straw Molecular Model

Introduction Straw molecular model is an educational material sample which is affordable and helpful to understand skeleton structure of molecules. Each atom is represented by one straw or combination of several straws and these straws are connected with connector straws in order to make a molecular model. For example when you make a carbon dioxide model, first of all you should combine 4 pale green straws which represent four arms of connection of a carbon atom. Then cut out two straws which have flexible part in the middle of them. Fold them parallel then they represent oxygen atoms which have two connective arms. Connect one oxygen straw and carbon with two connectors after that connect another oxygen and carbon again. You can see straw carbon dioxide molecular model.

General commercial molecular models have plastic spheres which represent atoms. But for this straw model it is impossible, therefore please imagine that the carbon atom exists in the middle of the crossing of pale green straws and flexible parts of the red straws are the centres of oxygen atoms. Nevertheless this low cost straw model can show double and triple bonds as well, so we can use this material from upper basic school level to secondary school level. Covalent radii When making molecular model it is important to express distance between atoms as accurate as possible. This explanation sheet basically uses covalent radii (table 1) as distances between atoms. Due to the types of the straws we can buy in Zambia, I multiplied 6.4x10 or 4.4x10 on each covalent radius and made length of straws for big models and small models. If you want to make much accurate models, I recommend using the bond lengths shown on table 2 and adjust lengths of straws.

* adjust the length properly (by cutting the straws or making overlapping) *2 check how to make a benzene model

Colour of straws and atom and its number of connective arms Samples of molecular models shown below use pale green straws as carbon (C) atoms, blue straws as hydrogen (H) atoms, red straws as oxygen (O) atoms and yellow straws as nitrogen (N) atoms. I used white or pale green straws as connector straws. Combinations of elements, number of connective arms and colours of straw are shown on table 4.

How to make a connector

Make one 40mm (or 26mm for small size models) white or pale green straw. Make 19-20mm (or 12-13 mm) straight slit from both ends longitudinally. These slits should be made 180 degrees opposite site. Insert each end of this connector into an open end of other straw atom part or atom group. It can connect both sides firmly without any glue. Samples of small molecules

Example 1: Making a carbon (C) atom and a methane model
1 In order to make a straw which represents one carbon atom cut a straw into 49+20mm(big model) or 34+20mm (small model) long. Make a slit in the straw at 20mm from one end of the straw. Do not cut one third of the circumference of the straw. After that make a longitudinal slit on 20mm part of the straw. Prepare 4 carbon atom straws.	2 Insert a slit side of the straw into another straw's hole which is next to the slit end. Repeat this 4 times as picture 2-7 shows.

4	5	6	7
8 After you insert straws into each other completely. Bend each straw like the picture above.	9 If you what to make an accurate model. Put carbon atom straw model in a straw regular tetrahedron with 4 connectors. See "Straw polyhedrons"	10 Apply super glue on the conjunction. Wait until the glue is completely dry.	11 In order to make hydrogen atom cut blue straw into 24mm (big model) or 16mm (small model). Then put half of a connector into the blue straw.
	12 Put the four hydrogen atom straw plus the connector into each end of carbon atom straw.

Example 2: Application of the methane model (Alkane CnH2n+2 & Cycloalkane CnH2n)
Ethane (C2H4, CH3-CH3)	Propane (C3H8, CH3-CH2-CH3)
Butane (C4H10, CH3-CH2-CH2-CH3)
Cyclohexane (C6H12) Boat	Cyclohexane (C6H12) Chair
Example 3: Alkene CnH2n When you make alkene and alkyne models, please do not apply super glue on the conjunction of C straws!
Ethylene (C2H4, CH2=CH2)	Propylene (C3H6, CH3-CH=CH2)
Example 4: Alkyne CnH2n-2
Acetylene (Ethyne) (C2H2, CH CH)	Propyne (C3H4, H3C-C CH)
Other examples (next) "Straw Molecular Model 2" Alcohol, Ether, Aldehyde, Ketone, Carboxylic acid, Ester "Straw Molecular Model 3" Benzene, Application of the benzen model

"Straw Molecular Model" Copy right JICA Senior Volunteer Hideo Nakano (Oct 2005)