The understandable notes, Structure of atom, Class- 9 , Part-3

 Bohr' Representation of Atom 

• In the centre there is nucleus represented by a filled circle.
• Around the circle there are rings which are represented as shells. 
• The dots on shells represent electrons.
• The closest ring can have maximum two dots as K shell can reside only two electrons
• ( Nucleus to dark circle se represent krte hai)
• ( Nucleus ke around shells ko ring se represent krte hai. )
• ( Nucleus ke sabse paas vali ring pr maximum two electrons aa sakte hai isi liye maximum two dots hi ban sakti hai.

Give the diagram of sodium atom according to bohr

( Ab is diagram mai aap centre mai nucleus dekh sakte ho or uske side mai K, L, M shells ko. In shells mai aap har shell me alag electrons dekh sakte ho. Jaise ki innermost shell mai sirf 2 electrons hai aur outermost mai sirf ek. Baki second shell, shells ki ginti hamesha centre se bahar ki taraf krna, mai aap 8 electrons dekh sakte ho, to kisi bhi atom ka bohr diagram banane ke liye aapko pata hona chahiye ki uske andar kitne electrons hai. Agar yaha par NA^+ ion ka diagram banana hota to valence shell jo ki sabse bahar ka shell hota hai usme se ek electron deduct ho jata. Ab jo ye soch rhe hai ki fir to shell represent krne ki koi jarurat hi nhi hai to ji haan aap bilkul shi soch rhe ho. Ab potassium ka diagram apni notebooks mai banakar google se check karo.  )

VALENCY 

Atoms of all elements reacts in a way to attain a noble gas configuration.

The noble gas or inert configuration is those which have completely filled valence shell.

Examples of noble gases are helium, argon, neon etc.

( Dekho pichle chapter mai tumne padha hoga, agar nhi padha to koi baat nhi mai padha dunga bas thoda time do, haan ki elementsreact krke compound bamds banate hai vagera vagera. Ab koi elementreact kyo krega, kya jarorat hai use react krne ki, to iska jawab hai ki vo noble gas configuration ban na chahata hai. Noble gas configuration vo hoti hai jisme outermost electron completely filled rehta hai. Ab ye maine valency ke topic mai kyo padhaya ye niche samajh aaega )

The combining capacity of element or atom is called valency. Valency refers to the ability of an atom to combine with other atoms, and it is determined by the number of electrons an atom can gain, lose, or share to achieve a stable electron configuration, typically aiming for a full outer shell.

For example

• Lithium has the valency of 1.
• Hydrogen has the valency of 1.
• Aluminium has the valency of 3.
• Potassium has the valency of 1.

( Dekho valency kisi bhi atom ki combining capacity hoti hai. Yani ki koi atom kitne aur atoms ke sath bond bana sakta hai. Ab chemical reaction mai to keval electrons react krte hai. Haan to valency bhi electron pr depend krti hai. Ab valency kaise nikalte hai ye valency samjhne ke baad apne aap samajh aa jayega. Ab humne pehle ye padha ki har atom reacts krke noble gas banna chahata hai. To isse hum ye keh sakte hai ki atom electron ko ya to gain krke, ya to loose krke aur ya for share krke bond banaega.)

To find the valency of any atom, we need to know the number of valence electrons of atom. If the atom has less than or equal to four electrons then the valency is same as of valence electrons but if the valence shell contain more than four electrons then subtract the valence electrons from 8 to get the valency. 

( Ab kisi bhi atom ki valency nikalne ke liye hume uske valence shell mai kitne electrons hai ye pata hona chahiye. Agar kisi bhi atom ke valence shell me 4 ya usse kam electrons hai to uski valency vhi hogi aur agar uske valence shell mai 4 se jyada electrons honge to uski valency nikalne ke liye valence electrons ko 8 me se subtract kr denge. Ye rule helium ko chod kr sab jagah applicable hai. Kyonki helium ki valence shell mai do electrons hote hai par kyonki vo completely filled hai to uski valency 0 hongi. )

ATOMIC NUMBER AND MASS NUMBER 

Atomic number is defined as the total number of protons in an atom. It is also defined as the number of electrons in a neutral atom. All atoms of same element have same atomic number. It is represented by 'Z'. 

Maas number is defined as the sum of protons and neutrons in an atom. The maas of the whole atom is concentrated in the nucleus and nucleus is made up of protons and neutrons that's why the maas of the atom is the sum of protons and neutrons. 

If we know atomic number then we can find number of protons in an atom beacuse it is same. Similary if we know maas number and atomic number then we can find the number of neutrons. The number of neutrons in an atom is represented by 'N'. And maas number is represented by 'A'. 

So

Atomic number = Number of Protons 

Number of Protons = Number of electrons in neutral atom. 

Mass number = Number of Protons + Number of Neutrons

Number of neutrons = MASS NUMBER - Number of protons.

( Atomic number directly equal hote hai number of protons ke. Ab protons chemical reactions mai react nhi krte to ye definition best hai. Par agar electron ke referencemai batana ho to atomic number ek neutral atom ke number of electrons ke equal hota hai. Ab atom neutral tabhi hota hai jab proton aur electron same number mai present ho. 

Iske baad maas number jo ki sum hota hai protons aur neutrons ka. Ab agar aapko maas number aur no of neutron pata ho to atomic number nikal sakte hai. Aur upar likhe hue formulas ko samajh lena kyonki yaad krne ki koi jarurat nhi hai. Baki formula based mcqs aate hai is part se to ignore mat krna important concept hai. Is class mai to sirf ye teen hi sub atomic particle hai lekin vaise aur bhi hote hai jinke bare mai abhi padhne ki jarurat nhi hai. )

A atom is represented by its symbol, maas number and atomic number. Where the symbol denotes.the atom. On the left superscript there is maas number and on the left subscript there is atomic number as shown in the diagram.

( Atom ko symbol ke left side mai upar ki taraf maas number 

ISOTOPES 

Atoms of the same element having same atomic number but different mass number is called isotopes. Isoptopes have same chemical property but different physical properties.

For example Hydrogen has 3 isotopes

With mass 1u - protium

With maas 2u- deuterium 

With maas 3u- tritium 

Isotopes of other elements doesn't have specific name as hydrogen does.

Similarly in a sample of chlorine, two isotopes are present one of maas 35u (approximately 75%) and second of maas 37u (approximately 25%) so while taking the maas and composition in average the maas of chlorine is generally considered 35.5u.

The maas of any natural element is taken as the average maas of all isotopes. But if a atom has no isotopes then we just find the maas number by adding number of protons and number of neutrons.

( Same elements ke different atom, ye kaise ho sakta hai, bilkul ho sakta hai kyonki ye chemistry hai. Ab isotopes un elements ke atoms ko bolte hai jinka atomic number to same hai pr maas number different hai. Ab atomic number same hone se ye to saaf hai ki number of protons same hai pr difference hai number of neutrons mai. Jaise ki hydorgwn ki teen isotopes hote hai. Ek jisme ek bhi neutron nhi hota aur sirf ek proton hota hai jise hum protium kehte hai, dusra jisme ek neutron aur ek proton hota hai aur use hum deuteriumkehte aur teesra jisme two neutron aur ek proton hota hai aur ise hum tritium kehte hai. Hydrogen ke alawa kisi aur elements ke isotopes ke specific name nhi hote. Unhe hum aise hi isotope of element keh kr sambhodhit krte hai.

Aur ek chlorine ka example diya hua hai, chlorine ke do isotopes existkrte hai jinme se ek ka maas 35u hota hai aur dusre ka 37u. Ab avergae nikaloge to 36 aaega pr kyonki 35u wale isotope ka composition jyada hai isi liye average maas 35.5u hoga. Aur u ka matlab atomic maas unit hota hai. Ab jo log ye soch rahe hai ki inka koi kaam bhi hai ya bas aise hi padha rahe ho to unke liye next topic hai jinme inki applications hi puchi hui hai.  )

Applications of Isotopes 

(i) An isotope of uranium is used as a fuel

in nuclear reactors.

(ii) An isotope of cobalt is used in the

treatment of cancer.

(iii) An isotope of iodine is used in the

treatment of goitre.

(Vaise to in isotopes ke proper number hote hai pr itna yaad krne ki jarurat nhi hai. Acha tumhe pata hai ki jo hydrogen bomb banta hai vo deuterium aur tritium ka use krke banta hai. Nuclear reaction ke through jab inhe helium mai convert krte hai to bahut jyada energy release hoti hai. Yehi reaction sun ke surface par bhi hota hai. Bas ek aur topic rehta hai bas ye chapter khatam.) 

ISOBARS

Atoms of different element having same maas number is called isobars. For example Calcium and Argon. 

( Different element jinka maas same ho unhe isobars kehte. Jaise argon ka atomic number 18 hai aur calcium ka 20 par dono ka maas number 40u hai. Chalo ye chapter khatam. )