How do molecules differ from one another?
Well don't they have different elements?
And so, their reactivity, polarity, structure, melting point, boiling point, density, and many more properties change. Does mercury amalgam alloy
Also, we see that some molecules are more reactive than others. Acids and bases tend to be more reactive than neutral oxides. When we put metals in acids, we see bubbling and the metal gets used up, but if we put them in neutral oxides such as carbon monoxide
Some molecules are polar, such as hydrogen fluoride
I just gave some examples, and there are many more.