We have already discussed the model of an atom and also were the subatomic particles are present inside an atom.
As we know that the protons are present inside the nucleus , so the atomic no. of an element is defined as the number of protons present in an atom.
Therefore, atomic number of an atom = number of protons in an atom
The symbol for atomic number is Z
Atoms of same element have same number of protons inside the nucleus, thus atom of same element have same atomic number. and atoms of different elements have different atomic number.
The neutral atom have same number of protons and electrons. So in that case the number of electrons is equal to the number of protons.
Thus for neutral atom
Atomic number = number of protons = number of electrons
When we talk about the following atom
The total number of Protons and Neutrons present in an atom is called its mass number.
Mass number = Number of protons + Number of Neutrons
Mass number is denoted by the symbol A
Mass number = Atomic number + Number of Neutrons
As we know that Atomic number = Number of Protons
Representation of atomic and mass number
Let symbol of an element be Y, so it can be written as
Q1. WRITE THE ELECTRONIC CONFIGURATION OF ATOMIC NUMBER 16
ANSWER: K SHELL 2
L SHELL 8
M SHELL 6
Q2. CALCULATE THE SUB-ATOMIC PARTICLES OF AN ATOM WHOSE MASS NUMBER IS 22 AND ATOMIC NUMBER IS 10
ANSWER: MASS NUMBER = NUMBER OF PROTONS + NUMBER OF NEUTRONS
MASS NUMBER = ATOMIC MASS + NUMBER OF NEUTRONS
22 = 10 + NUMBER OF NEUTRONS
22-10 = NUMBER OF NEUTRONS
THEREFORE, NUMBER OF NEUTRONS = 12
NUMBER OF PROTONS = 10
NUMBER OF ELECTRONS = 10