Why is atomic number better than atomic mass for organizing the elements in the periodic table?

It is because they increases linearly due to adding of 1 proton at each step.

The yeast and Hydrogen Peroxide is the chemical change, because when something is changed chemically, there is a chemical added that cannot be taken away to make it go back to it's original state. However when you're blowing bubbles in milk, no chemicals were added and it will go back to it's original state.