molecule
Two or more atoms bonded together
Chemical bond
Connection between
atoms
model
representation of an object
Chemical formula
The atoms (letters and numbers) that make up a molecule 
Chemical structure
The specific way that atoms are arranged 
Crystal
 Structure of atoms or molecules in a 3-D pattern 
Polymer
Structure of molecules in a repeating chain pattern 
Extended structure
A molecule whose atoms occur in a constant ratio and repeating pattern 
Ratio
A quality relationship between two things