How is the mass number different from the atomic number of an atom?

Answer 1

Atomic number of an element is the number of protons that an atom of an element contains. The atomic weight (the mass of the atom) is measured by not only the mass of the proton(s), but by the mass of the nuetrons and electrons too.

Answer 2

The atomic number indicates the number of protons in an atom's nucleus. The atomic number for a given element doesn't change (without changing the identity of the element). For example, six protons in a nucleus means the atomic number is six, which corresponds to carbon.

The Atomic Mass has to do with how much the actual atom weighs. The atomic mass is roughly expressed as the sum of all protons and neutrons in the atom's nucleus. The mass of electrons are so small that they are negligible. The number printed on the Periodic Table is not a simple integer for primarily one reason: elements exist in different isotopes.

Isotopes are atoms that have the same atomic number but different atomic masses, and thus differ only in number of neutrons. In nature elements exist as a mixture of various isotopes in different abundances. The mass on the periodic table is a weighted average of the mass of all isotopes. Sometimes, for synthetic and/or unstable elements, the approximate mass or the mass of the most stable isotope is given.

Answer 3

1. The atomic number is equal to the number of protons in the atomic nucleus (or the number of electrons in a neutral atom) of a chemical element.

2. The mass number is a sum: NUMBER OF PROTONS + NUMBER OF NEUTRONS in the atomic nucleus of an isotope.

Answer 4

The atomic number is the number of protons. The mass number is the number of protons PLUS the number of neutrons. The mass number is always bigger than the proton number (except in hydrogen) because neutrons have a mass of 1 derived unit, as do protons. The difference with hydrogen, is that they have no neutrons, so the atomic and mass number are the same.

Hope that helped!

Answer 5

The mass number is the total number of protons and neutrons in the nucleus of an atom, while the atomic number is the number of protons in the nucleus. Mass number determines the atom's mass, while atomic number identifies the element on the periodic table.

Answer 6

mass includes both protons and neutrons.

number includes only protons

Answer 7

The atomic mass is the actual mass (and is a real number; that is, it can have a fractional part). The atomic number is the number of protons (and is an integer).