what is the difference between mass number and relative atomic mass?

Answer 1

In addition to Maya's correct answer:

Relative atomic mass often is the average over the standard population of isotopes. Carbon 12 has the relative atomic mass 12, but natural carbon has the relative atomic mass 12.011 due to the presence of carbon 13 and traces of carbon 14. That also explains the unlikely 35.5 AMU for chlorine - an average of isotopes 34 (about 25%) and 36 (about 75%).

Having worked with isotopic measurements on foraminifer shells, assuming a constant isotope distribution in natural material can be somewhat fallacious if those isotopes are involved in climatic or geological processes where one isotope may be preferred in a reaction. Hence don't read too much into the later digits of the RAM values - rounding them won't make you wronger than slavishly using every last digit.

Answer 2

Mass Number
The mass number (A), also called atomic mass number or nucleon number, is the number of nucleons (protons and neutrons) in an atomic nucleus. The mass number is unique for each isotope of an element and is written either after the element name or as a superscript to the left of an element's symbol. For example, carbon-12 (12C) has 6 protons and 6 neutrons. The full isotope symbol would also have the atomic number (Z) as a subscript to the left of the element symbol directly below the mass number: {}_{6}^{12}\mathrm{C}. Note that this is redundant, as there is a one-to-one mapping between atomic number and element symbol, so it is rarely used, except when we want to clarify the number of protons in a nucleus, such as in atomic reactions.

The difference between the mass number and the atomic number gives the number of neutrons (n) in a given nucleus: n=A−Z.

For example: Carbon-14 is created from Nitrogen-14 with seven protons (p) and seven neutrons via a cosmic ray interaction which transmutes 1 proton into 1 neutron. Thus the atomic number decreases by 1 (Z: 7→6) and the mass number remains the same (A = 14), however the number of neutrons increases by 1 (n: 7→8).

Before: Nitrogen-14 (7p, 7n)
After: Carbon-14 (6p, 8n).

This should not be confused with the relative atomic mass which is the average abundance atomic mass number of the differing isotopes found. For instance, there are two isotopes of chlorine: Chlorine-35 and Chlorine-37. In any given sample of chlorine that has not had any mass separation there will be roughly 75% of chlorine atoms which are chlorine-35 and only 25% of chlorine atoms which are Chlorine-37. This gives chlorine a relative atomic mass of 35.5 (actually 35.4527 g/mol).

Relative Atomic Mass
The atomic mass of a chemical element is the mass of an atom at rest, most often expressed in unified atomic mass units. The atomic mass is often synonymous with relative atomic mass, average atomic mass and atomic weight; however, it is subtly different in that it can either be the abundance-weighted average of isotope masses of an element or the mass of a single isotope.

The relative atomic mass (also known as atomic weight and average atomic mass) is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance. Periodic tables usually list these with reference to the local environment of Earth's crust and atmosphere. An uncertainty in parenthesis is often included. For artificial elements the nucleon count of the most stable isotope is listed in brackets as the atomic mass.

You could get more information at the 2 links below...

Answer 3

These two things are entirely different.
mass number is the number of electrons/protons in an atom
whereas,
relative atomic mass is the mass of an atom with respect to the atom of carbon 12 isotope.

Eg. mass number of calcium is 20 whereas its atomic mass is 40

Answer 4

Mass number: the sum of the protons and neutrons that make up that nucleus (or sum of nucleons).

Relative atomic mass: The mass of an atom relative to one atom of carbon. Carbon has a RAM of 12.

Answer 5

Same the the difference between mass murder and relative atomic explosion?

Answer 6

Think of polo the mint with a hole, hope this help's.

Answer 7

the units are different