Are argon, oxygen, and water particles similar to neon particles? Why or why not?

First of all let's define the different kinds of chemical compounds we are talking about because that will define the kinds of particles we are talking about.  Argon is an element on the periodic table.  It is a member of the noble gasses, meaning that it is a monoatomic pure gas.  In other words, argon gas particles are simply pure single atoms of argon. Oxygen is also an element on the periodic table but in...

First of all let's define the different kinds of chemical compounds we are talking about because that will define the kinds of particles we are talking about.  Argon is an element on the periodic table.  It is a member of the noble gasses, meaning that it is a monoatomic pure gas.  In other words, argon gas particles are simply pure single atoms of argon. Oxygen is also an element on the periodic table but in nature, the simplest form of oxygen is oxygen gas, a diatomic molecule composed of O2 (two oxygen atoms bonded together).  Since O2 is a diatomic molecule, its smallest particle size is a molecule.  Finally, water is a polyatomic molecule H2O composed of two atoms of hydrogen and one atom of oxygen.  Again, particles of water are the individual molecules.  

Neon is also a noble gas just like argon.  So neon particles are individual neon atoms.  Neon particles are similar to argon particles but not similar to oxygen or water molecules.