Short Answer Type
Long Answer TypeHow is position of electron and proton in an atom established? Describe an experiment in this regard.
Or
Describe Rutherford's scattering experiment. How did it lead to Rutherford’s nuclear model of atom?
Or
Describe an experiment which provides evidence that most of the charge and mass of an atom is concentrated in its nucleus.
Short Answer TypeLong Answer TypeWhat are atomic number and mass number? How are they related to each other?
Atomic number (Z): In 1913, Mosley devised an experiment to find the positive charge on the nucleus of an atom. Atomic number of an element is equal to the number of unit positive charges or protons present in the nucleus of an atom of that element.
An atom is electrically neutral, therefore, in an atom,
Number of protons = No. of electrons
Atomic number = No. of protons in the nucleus of the atom
= No. of electrons present outside the nucleus of the same atom.
Atomic number is a fundamental property of the atom and is generally denoted by Z.
Mass number (A):The mass of an atom is mainly concentrated in the nucleus. In the nucleus, there are protons and neutrons, these are collectively called nucleons. Mass number of an element is the sum of the number of protons and neutrons present in its atom. It is generally denoted by A.
Mass No. (A) = No. of protons + No. of neutrons = No. of nucleons.
Relation between mass number and atomic number:
We know,
Mass number (A) = No. of protons + No. of neutrons
= At. No. (Z) + No. of neutrons.
No. of neutrons = Mass No. (A) - Atomic No. (Z)
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