How to create a dichotomous key
Step one: make a list of your items
1)
2)
3)
4)
5)
Step two: Draw a tree diagram

find a characteristic that would allow you to put all the items
into 2 groups
(e.g. living/non-living; or metal/non-metal; or hard/soft, etc.)



Create a branch for “yes” and another for “no” and place the
items into the correct group.
Find another differentiating characteristic for each new
group  “yes” and “no” branches
Repeat until you have one item per arrow
Step three: Place a number for each “characteristic” and (a) for yes, (b) for no.
Step four: Start writing out your paired statements:
Example:
1) (a) It is living
(b) It is not living
2) (a) It is…
(b) It is not…
Go to step 2
Go to step 4