CHEMICAL CONSTITUENTS of LAVENDER
Some 300 molecules were discovered in true lavender's essential oil, that are responsible for its fine, complex yet clear aroma - most of which are trace elements. The major constituents are (the ones in bold are the most dominant/famous ones):
Linool
Linalyl acetate (up to 40%) 
Lavandulol *
Lavandulyl acetate *
Cineole
Coumarin
Camphor
1-octen-3-yl acetate
Tricyclene  
alpha-Pinene  
alpha-Thujene  
Camphene  
beta-Pinene  
Sabinene  
gamma-Terpinene  
Myrcene  
alpha-Terpinene  
5-Methyl-3-heptanone  
Limonene  
Eucalyptol  
delta-3-Carene  
(E)-beta-Ocimene  
Octan-3-one  
para-Cymene  
Terpinolene  
Hexyl-isobutyrate  
Neo-allo-ocimene  
3-Acetoxy-octene  
Hexyl-butyrate  
cis-Linalool oxide  
Vinyl amyl carbinol  
trans-Linalool oxide  
Camphor
Dihydrolinalool  
(E)-Caryophyllene  
Terpinen-4-ol  
(E)-beta-Farnesene  
alpha-Terpineol  
Borneol  
Neryl acetate  
Geranyl acetate  
Nerol  
Geraniol  
Caryophyllene oxide  
alpha-Humulene  
Hexyl acetate  
alpha-Santalene

As we can see, it mostly contains terpenes, terpene alcohols and esters, and a few alcohols. According to Jeanne Rose "esters are soothing, calming, and fungicidal"; and linalool is an "antibacterial, believes discomfort, diuretic, tones without irritating, stimulates the immune system, sedating"; the latter actions similarly described as initiated by the terpene alcohols as well as toning (The Aromatherapy Book, pp. 158-160).

* Both lavandulol and lavandulyl acetate are insect pheromones, which might explain the abundance of bees observed around lavender shrubs.