Sodium

• few sodium rich non water soluble compounds (analog to the high water solubility of nitrides on the complementary oxoacid side)
• use of sodium to make insoluble compounds soluble (in mining)

Misc

• Chemical gardens: [1]
  Adding metal salts to an aqueous solution of sodium silicate (otherwise known as waterglass) or potassium silicate.
  In a double displacement reaction the newly formed metal silicate falls out while the newly formed sodium salt becomes even more suluble and thus stays in solution.
• Sodium silicate [2]

Related

• Nitrogen and nitrates are the anionic counterpart in making compounds maximally water soluble. Followed by sulfates. See: Salts of oxoacids.