Elements are the same type of atoms, so there is nothing else to separate. Hydrogen has hydrogen atoms, and no other kind. Therefore nothing can be taken out of it anymore. Chemical x is a mixture, made by y and z. Nothing can make up y and z but themselves.
It's examples are:
1)London dispersion forces
2)Dipole-Dipole forces
3)Hydrogen bonding...
16-18= -2 so it has a negative charge. Just subtract the electrons from the protons if you get a positive number it will have a positive charge and vice versa.
