Answer:
The volume of the system will change and maybe the shape of the system boundary
CH4 is an emprirical formula as it shows the simplest ratio of the numbers of different atoms present in the molecule. The empirical formula for CH4 is also the same as the molecular formula.
The other compunds can be simplified so they are not the empirical formula of compounds.
Hope this helps :).
Simply look at the periodic table and fill in what you know based on the table
The number of protons = atomic number
The number of electrons, Which is the same as the atomic number for atoms.
The number of valence electrons that is given by the group that the element is in, the top number of each column in the periodic table.