[JCL07]

For an element, how do I find the:
- atomic mass
- mass number
-# protons
-# neutrons
-# electrons

For example, I know Hydrogen has 1 proton and 1 electron but I don't understand how to find it's atomic mass and mass number.

Also, I don't know how to find the atomic mass, mass number, neutrons, and electrons for:
- H+
- 12C
    6
- 7Li+
   3
- 35Cl-
  17
- 39K
  19
- 24Mg2+
  12
- As3-
- Ag
- Ag+1
- S-2
- U

[fledarmus]

Start with the definitions - what is the definition of mass number? What is the definition of atomic mass?

[DevaDevil]

Also, I don't know how to find the atomic mass, mass number, neutrons, and electrons for:
- H+
- 12C
    6
- 7Li+
   3
- 35Cl-
  17
- 39K
  19
- 24Mg2+
  12
- As3-
- Ag
- Ag+1
- S-2
- U

for these, start with the neutral atoms. Then see in what way the given cations/isotopes are different from the neutral atoms.