ATOMIC NUMBER MEANS THE NUMBER OF PROTONS OR ELECTRONS PRESENT IN AN ATOM.WHEREAS THE ATOMIC MASS MEANS THE MASS OF AN ATOM.NEARLY ATOMIC MASS IS DOUBLE IN NUMBER WITH ATOMIC MASS
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							Atomic Mass
# One atomic mass (1u) is defined as exactly one-twelfth the mass of an atom of carbon-12.
# Atomic mass unit is denoted by letter `u`.
Mass Number 
# The total number of protons and neutrons present in one atom of an element is known as its mass number.
# The mass number of an element is denoted by letter `A`.
						

							Atomic mass is the average of several elements` masses ((the formula is AM = (% abundance)(mass1) + (% abundance)(mass2) +...)) 
Mass number is just the mass of one element.
						

							
atomic number is the number of protons (or neutrons) in an element . eg- atomic number of oxygen is 8 and that of lithium is 3. atomic  mass is the number of protons +the number of neutrons .it is approx. double the atomic number .eg- atomic mass of oxygen is 16 and carbon is 12. hope this helps you.......