The understandable notes- Structure of Atom, Class 9, Part-2

 BOHR' MODEL OF AN ATOM

(i) Only certain special orbits known as

discrete orbits of electrons, are allowed

inside the atom.

(ii) While revolving in discrete orbits the

electrons do not radiate energy

(Ab dekho rutherford ji ka model kai chize to explain kar paya tha par kayi nhi. To ab ek naya model banaya gaya jo ki Neils Bohr ne banaya usme unhone mainly do baate kahi. Pehli to ye ki jo electrons revolve krte hai around the nucleus vo ek fixed path mai krte hai. Discrete ka matlab hai ek orbit continuously dusre mai merge nhi ho rha hai. Balki orbits alag hai. Inhi orbits mai jo electron hai vo revolve krega. Aur dusri chiz inhone kahi ki jab electron nucleus kai around revolve krte hai tab vo energy to releaseyar fir radiate nhi krte. Yani ki vo anant kaal tak rotate krte hi rahenge agar unhe koi external energy na mile. Yaar dekho tumhe to teen hi models hai lekin iske aur bhi kai models hai. Bohr's model mai hi aage specterum ka concept hai par tumhe jo bataya hai bas vo yaad rakhna. Agar kisi ko sare models padhne hai jo ki syllabus mai bhi nhi hai to class 11 ka chemistry ka chapter 2 padh lena. Meri site pr to abhi nhi hai kyonki uske bare mai mujhe abhi research krni hai. )

Thomson's  model of atom was proposed in 1904.

Rutherford's model of atom was proposed in 1911.

Bohr's model of atom was proposed in 1913.

Now the energy levels or shell in which electrons will revolve are represented by letters K, L, M, N ...... or they can be represented by numbers like 1, 2, 3, 4...... . 

(Dekho ye models kab kab diye gaye the ye to yaad hi rakh lena. Aur jin energy levels ya fir energy shells ki baat Bohr ne kahi thi ki unhe alphabets se represent krte hai. Kaise krte hai ye agle topic kai baad ka topic hai. Abhi kai liye bas itna samajh lo ki inhe K,L,M,N... in alphabets se represent krte hai.)

NEUTRONS

IN 1932, James Chadwick founded another sub atomic particle which is names as neutrons. He bombarded aplha particles on beryllium and observed a neutral radiation.  The maas of neutron is nearly equal to the maas of proton. In precision, neutron is slightly heavier than proton. 

The maas of neutron is nearly equal to proton. 

Neutrons has no charge on it.

They are placed tightly with the protons in the nucleus beacuse of the nuclear force of attraction. 

The total maas of atom is the sum of proton and neutron in it.

They are present in every element except hydrogen. But they are present in isotopes of hydrogen.

( 1932 mai chadwick ji ne ek experiment ke through ek aur sub atomic particle ki khoj kr di jinhe inhone naam diya neutron. Ab dekho neutron ka maas proton ke equal hota hai. Agar high precision ho yani ki decimal ke baad teen char digits mai dekha jaye to neutron protons se thode se bhari hote hai. Agar exam mai likhna to ye hi likhna ki proton aur neutron equal maas ke hote hai. Neutrons kai upar koi charge bhi nhi hota yani ki ye neutral hote hai. Ab agar aisa lag rha hai ki inme maas to hota nhi to ye react nhi krenge to ye nuclear reaction mai react krte hai jo ki generally radioactive elements ke through hota hai. Ab dekho inka maas proton ke equal hota hai to inhe maas consider krte hue electron ki tarah ignore to kr nhi sakte. To atom ka maas jab bhi diya ho tab usme proton aur neutron dono ka sum kiya jata hai. Jaise ki lithium ka atomic number hota hai 3 aur maas number 5 to uske andar 2 neutron honge.)

How Electrons are distributed in different orbits.

The rules for electron distribution are given by Bohr-Bury scheme.

• The maximum number of electron that can a orbit hold is given bu 2n^2 where n is the number of orbit. For example the orbit closest to nucleus is K and its number is 1, so the maximum number will be 2×1^2=2. Similary for L it is 8 and for M it is 18.

( To pehla rule ye hai ki maximum electrons ho ki kisi orbit mai fit ho  sakte hai ye 2n^2 ke formula se niklenge. Jaha par n orbit ka number hoga. Ab formula apply karo aur jis marji orbit ki maximum electrons capacity nikal lo. Pr koi fayda nhi hoga, kyo ye aage ke rules bata denge aur agar kisi orbit ka number 5 hai to vo kitne maximum electron fit kr sakta hai ye bata dena comment me. Aur web pr bhi comment hote hai. )

• Electrons will fill from increasing energy order. They will fill from lowest to highest energy shells. 

(Electron nucleus ke sabse paas wale orbit se fill hona shuru krte hai. Iska matlab ye hai ki jab tak K shell completely fill nhi ho jata tab tak L shell mai electrons fill nhi krenge. 11th ki chemistry kai dusre chapter mai bhi ye likha hai aur is principle ka naam Aufbau principle. ) 

•  The maximum number of electrons that can be filled in a shell is eight. Although 2n^2 shows that 18 electrons can reside in the shell the shell can reside only 8. This is called octet rule.

(Kisi bhi orbit mai 8 se jyada electrons fit nhi aa sakte chahe fir pehla rule 118 bhi bataye kuch garak nhi padta. Ye chemical stability ke liye hota hai. Aur ise octet rule bolte hai. Agle part mai ye chapter khatam. )