Discuss idea of molar mass of elements, related to/same value as elements atomic mass in amu, but molar mass has a different unit.

Also discuss idea that a compounds composition has a major impact on its properties example compound pairs that differ in composition and properties include CO and CO₂, FeCl₂ vs. FeS, NaCl vs. HCl, etc. properties to talk about could include melting and boiling point temperatures, solubility in water, acidity, etc.