9th Chemistry, Ch 1 - Atomic and Mass Number - Lecture 6

Atomic Number:-
Atomic number of an element is equal to the number of electrons, or protons present in the nucleus of the atom of that element. It is represented by 'Z'.

Element k atom k nucleus me majood protons ki tadad ko hm atomic number bolte hn or atomic number ko 'Z' se represent kiya jata ha.

All the atoms of an element have same number of protons in their nucleus. It means that every element have its specific atomic number and it is also termed as the identification of the element.
For Example:- All atoms of hydrogen have 1 proton in their nucleus so the atomic number of Hydrogen is 1. Same like that, Carbon atoms have 6 protons in their nucleus and oxygen have 8 protons, So the atomic number of carbon and oxygen is 6 and 8 respectively.

Kisi b element me majood tmam atoms k nucleus me majood protons ki tadad ek jesi hoti ha. Iska mtlb ha k har element ka ek fixed atomic number hota ha. Jis number se hm us element ko asani se phchan sekte hn. Isi number ko hm atomic number bolte hn.
For Example:- Hydrogen k nucleus me 1 proton majood hota ha is liay hydrogen ka atomic number 1 ha. Isi trha carbon k nucleus me 6 protons or oxygen k nucleus me 8 protons hote hn is liay carbon ka atomic number 6 or oxygen ka atomic number 8 hota ha.

Mass Number:-
Mass number of an element is equal to the sum of the number of protons and neutrons present in the nucleus of the atoms of that element.It is represented by 'A'.

Element k atom k nucleus me majood protons or neutrons dono ki tadad ko hm mass number bolte hn or mass number ko 'A' se represent kiya jata ha.

Most of elements have same number of protons and neutrons in their atom but not all the atoms.
For Example:- Hydrogen atoms have 1 proton and no neutron, So its mass number will be 1. Carbon atom has 6 protons and 6 neutrons, So its mass number will be 12. Sodium atom has 11 protons and 12 neutrons, So its mass number will be 23.

Elements k atoms k nucleus me protons or neutrons dono ki tadad ko hm mass number bolte hn. Protons or neutrons ki ye tadad kuch elements me same b hoti ha or kuch elements me in dono ki tadad mukhtlif b hoti ha.
For Example:- Hydrogen k atom k nucleus me 1 proton hota ha jb k koi b neutron nhi hota, is liay hydrogen ka mass number b is k atomic number ki trha 1 ha. Is k ilawa carbon k atom me 6 protons or 6 hi neutrons majood hote hn is liay carbon ka mass number 12 ha.

Relative Atomic Mass:g

The relative atomic mass of an element is the average mass of the atoms of that element as compare to the 1/12th the mass of an atom of carbon-12 isotope.

Atomic Mass Unit:-
The unit of relative atomic mass is 'atomic mass unit'. It is represented as 'amu'.

1 amu = 1.66 × 10(-24)g

As you know that the side of an atom is very small. So, it can not be determined practically. That's why scientists gives a way to determine the size of an atom by comparing the size with the atom of carbon-12 isotope. So, by comparing the sizes with C-12 we can easily determine the size of any atom.

Jesa k apko pta ha k atom ek bht hi chota particle ha jise hm aam ankh se dekh b nhi skta, to itne chote particle ka structure maloom krna yakeenan bht mushkil kam ha, is liay scientists ne atom k structure ka pta krne k liay ek method nekala ha jise hm Relative atomic mass bolte hn. Is process k zreay hm kisi b atom k mass ko carbon-12 isotope k mass k sath compare kr k maloom kr skte hn. Relative atomic mass k unit ko atomic mass unit bolte hn jise 'amu' likha jata ha. 1 amu = 1.66 × 10(-24)g

Written By:- M.Ashir Azeem

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