Atomic number & Mass number?!?

Question

WHATS THE DIFFERENCE BETWEEN THEM?!

Answer 1

Atomic number is the number of protons in the nucleus, while mass number is the number of protons and neutrons in the nucleus. Thus, mass number is greater than or equal to atomic number. (It is almost always greater, because hydrogen is the only stable nucleus without neutrons.)

A given element always has the same atomic number, because it is the atomic number that defines the element. Different atoms of an element may have different mass numbers, though, because many elements have multiple naturally occuring isotopes, meaning nuclei with different numbers of neutrons. For this reason, mass number is usually given as a weighted average based on the mass numbers and natural abundance of the different isotopes. Mass number is usually rounded to the nearest whole number, but sometimes it is not close to an integer value. For example, the mass number of oxygen is 15.9994, extremely close to 16 (the mass number of the most stable isotope), while that of hafnium is 178.49; it has 5 stable isotopes. Atomic number is always a whole number; oxygen's is 8 and hafnium's is 72.

Answer 2

Firstly atomic number and proton number are the same thing. Rite what they are is basically the number of PROTONS in the atom. Since an atom is always neutral in charge, there must be the same amount of - electrons to cancel out the + protons. So proton number is the no. of protons, and also electrons.

Atomic MASS is the mass of the nucleus of the atom , or the number of PROTONS + NEUTRONS.

Thus:

Atomic Number = Number of Protons
Atomic Number = Number of Electrons

Atomic Mass = Number of Protons + Number of Neutrons
Number of Neutrons is therefore = Atomic Mass - Atomic Number
(or Protons & Neutrons - Protons).

NOTE: when you get a question about an element in the periodic table, and they give you a top and bottom number, the smaller is always the Atomic Number

Answer 3

atomic # is the number of protons in the atom.
mass # is the mass of the atom with protons and neutrons both equal to 1 unit.

therefore mass # = atomic # + # of neutrons

so you can use mass # and atomic # to find the average # of neutrons in that type of atom.

(it isn't a whole number because of isotrophes of that element: atoms with either more or fewer neutrons than the norm for that element)

ie: H has an atomic # = 1 mass number = 1.001 so it has 1 proton and on average 0.001 neutrons (most have 0, but there will be some isoptrophs which have one)

Answer 4

The Atomic # is the number of Protons in the nucleus. The Mass number is the sum of the number of protons and Neutrons in the nucleus.

So the Mass number - the Atomic Number = the number of neutrons in the nucleus.

Answer 5

atomic number is the number of protons in the nucleus. Atomic mass is the total number of protons and neutrons in the nucleus. The electron contribution to the atomic mass is almost nil.