Revision Notes: Structure of Atom | Chemistry for JEE Main & Advanced PDF Download

 Page 1


Atomic Structure 
Rutherford's nuclear model 
Rutherford carried out experiment on the bombardment of 
thin (10
–4
 mm) Au foil with high speed positively charged ? ?
particles.  
He concluded that, an atom consists of  
(i) Nucleus which is small in size but carries the entire mass
i.e. contains all the neutrons and protons.
Properties of the nucleus 
(i) The small, heavy and positively charged portion of the
atom is known as nucleus. It is located at the centre of the
atom and discovered in 1911 by Ernest Rutherford.
(ii) Protons are positively charged particles.
(iii) Neutrons and protons are present in the nucleus hence
they are collectively known as nucleons.
Drawbacks of Rutherford's model 
(i)According to it “An electron moving around the nucleus
continuously loses its energy and should set up spiral motion 
Page 2


Atomic Structure 
Rutherford's nuclear model 
Rutherford carried out experiment on the bombardment of 
thin (10
–4
 mm) Au foil with high speed positively charged ? ?
particles.  
He concluded that, an atom consists of  
(i) Nucleus which is small in size but carries the entire mass
i.e. contains all the neutrons and protons.
Properties of the nucleus 
(i) The small, heavy and positively charged portion of the
atom is known as nucleus. It is located at the centre of the
atom and discovered in 1911 by Ernest Rutherford.
(ii) Protons are positively charged particles.
(iii) Neutrons and protons are present in the nucleus hence
they are collectively known as nucleons.
Drawbacks of Rutherford's model 
(i)According to it “An electron moving around the nucleus
continuously loses its energy and should set up spiral motion 
 
ultimately failing into the nucleus”’. Hence this model does 
not able to explain how the moving electrons could remain 
in its orbit. 
 (ii) It does not able to explain the discontinuous spectrum and 
the line spectra of ? H atom. 
 Planck's quantum theory 
 According to this theory, the energy of each quanta is directly 
proportional to the frequency ( ? ) of the radiation, i.e. 
      Lets,  
 ? ? E or 
c hc
E hv;v Thus,E ? ? ?
??
 
 Where, h is proportionality constant also known as Planck’s 
constant. 
                                  h = 
34
6.626 10 Joulessec.
?
?
 or 
   6.626×10
–27
 erg sec.  
 
 Photoelectric effect 
 Einstein’s photoelectric effect equation  
 According to Einstein, 
 Maximum kinetic energy of the ejected electron = absorbed 
energy – threshold energy 
 
?
?
?
?
?
?
? ? ? ?
0
0
2
max
1 1
2
1
? ?
? ? hc h h mv 
 Where, 
0
? and 
0
? are threshold frequency and threshold 
wavelength. 
 
Page 3


Atomic Structure 
Rutherford's nuclear model 
Rutherford carried out experiment on the bombardment of 
thin (10
–4
 mm) Au foil with high speed positively charged ? ?
particles.  
He concluded that, an atom consists of  
(i) Nucleus which is small in size but carries the entire mass
i.e. contains all the neutrons and protons.
Properties of the nucleus 
(i) The small, heavy and positively charged portion of the
atom is known as nucleus. It is located at the centre of the
atom and discovered in 1911 by Ernest Rutherford.
(ii) Protons are positively charged particles.
(iii) Neutrons and protons are present in the nucleus hence
they are collectively known as nucleons.
Drawbacks of Rutherford's model 
(i)According to it “An electron moving around the nucleus
continuously loses its energy and should set up spiral motion 
 
ultimately failing into the nucleus”’. Hence this model does 
not able to explain how the moving electrons could remain 
in its orbit. 
 (ii) It does not able to explain the discontinuous spectrum and 
the line spectra of ? H atom. 
 Planck's quantum theory 
 According to this theory, the energy of each quanta is directly 
proportional to the frequency ( ? ) of the radiation, i.e. 
      Lets,  
 ? ? E or 
c hc
E hv;v Thus,E ? ? ?
??
 
 Where, h is proportionality constant also known as Planck’s 
constant. 
                                  h = 
34
6.626 10 Joulessec.
?
?
 or 
   6.626×10
–27
 erg sec.  
 
 Photoelectric effect 
 Einstein’s photoelectric effect equation  
 According to Einstein, 
 Maximum kinetic energy of the ejected electron = absorbed 
energy – threshold energy 
 
?
?
?
?
?
?
? ? ? ?
0
0
2
max
1 1
2
1
? ?
? ? hc h h mv 
 Where, 
0
? and 
0
? are threshold frequency and threshold 
wavelength. 
 
 
 Bohr’s atomic model 
 The Bohr postulates are, 
 (1) An atom consists of positively charged nucleus  
 (2) The electrons revolve around the nucleus in circular orbits  
 (3) The circular orbits are those for which the angular 
momentum of an electron is an integral multiple of ? 2 / h where 
h is the Planck’s constant. 
 
?
? ?
2
nh
mvr L ; 1 ? n , 2, 3, …… ? 
 Where L is the orbital angular momentum and n is the number 
of orbit.  
 (4) When electrons move in permitted discrete orbits they do 
not radiate or lose energy.  
 
 Advantages of Bohr’s theory  
 (i) Bohr’s theory satisfactorily explains the spectra of species 
having one electron, viz. hydrogen atom, 
? ? 2
, Li He etc.  
 (ii) Calculation of radius of Bohr’s orbit: According to Bohr, 
radius of  n
th
 orbit in which electron moves is 
Z
n
k me
h
r
n
2
2 2
2
.
4 ?
?
?
?
?
?
?
?
?
?
 
 Where, ? n Orbit number, ? m Mass number ? ?, 10 1 . 9
31
kg
?
? ? e Charge 
on the electron ? ?
19
10 6 . 1
?
? ? Z Atomic number of element, k = 
Coulombic constant ? ?
2 2 9
10 9
?
? c Nm 
Page 4


Atomic Structure 
Rutherford's nuclear model 
Rutherford carried out experiment on the bombardment of 
thin (10
–4
 mm) Au foil with high speed positively charged ? ?
particles.  
He concluded that, an atom consists of  
(i) Nucleus which is small in size but carries the entire mass
i.e. contains all the neutrons and protons.
Properties of the nucleus 
(i) The small, heavy and positively charged portion of the
atom is known as nucleus. It is located at the centre of the
atom and discovered in 1911 by Ernest Rutherford.
(ii) Protons are positively charged particles.
(iii) Neutrons and protons are present in the nucleus hence
they are collectively known as nucleons.
Drawbacks of Rutherford's model 
(i)According to it “An electron moving around the nucleus
continuously loses its energy and should set up spiral motion 
 
ultimately failing into the nucleus”’. Hence this model does 
not able to explain how the moving electrons could remain 
in its orbit. 
 (ii) It does not able to explain the discontinuous spectrum and 
the line spectra of ? H atom. 
 Planck's quantum theory 
 According to this theory, the energy of each quanta is directly 
proportional to the frequency ( ? ) of the radiation, i.e. 
      Lets,  
 ? ? E or 
c hc
E hv;v Thus,E ? ? ?
??
 
 Where, h is proportionality constant also known as Planck’s 
constant. 
                                  h = 
34
6.626 10 Joulessec.
?
?
 or 
   6.626×10
–27
 erg sec.  
 
 Photoelectric effect 
 Einstein’s photoelectric effect equation  
 According to Einstein, 
 Maximum kinetic energy of the ejected electron = absorbed 
energy – threshold energy 
 
?
?
?
?
?
?
? ? ? ?
0
0
2
max
1 1
2
1
? ?
? ? hc h h mv 
 Where, 
0
? and 
0
? are threshold frequency and threshold 
wavelength. 
 
 
 Bohr’s atomic model 
 The Bohr postulates are, 
 (1) An atom consists of positively charged nucleus  
 (2) The electrons revolve around the nucleus in circular orbits  
 (3) The circular orbits are those for which the angular 
momentum of an electron is an integral multiple of ? 2 / h where 
h is the Planck’s constant. 
 
?
? ?
2
nh
mvr L ; 1 ? n , 2, 3, …… ? 
 Where L is the orbital angular momentum and n is the number 
of orbit.  
 (4) When electrons move in permitted discrete orbits they do 
not radiate or lose energy.  
 
 Advantages of Bohr’s theory  
 (i) Bohr’s theory satisfactorily explains the spectra of species 
having one electron, viz. hydrogen atom, 
? ? 2
, Li He etc.  
 (ii) Calculation of radius of Bohr’s orbit: According to Bohr, 
radius of  n
th
 orbit in which electron moves is 
Z
n
k me
h
r
n
2
2 2
2
.
4 ?
?
?
?
?
?
?
?
?
?
 
 Where, ? n Orbit number, ? m Mass number ? ?, 10 1 . 9
31
kg
?
? ? e Charge 
on the electron ? ?
19
10 6 . 1
?
? ? Z Atomic number of element, k = 
Coulombic constant ? ?
2 2 9
10 9
?
? c Nm 
 
 After putting the values of m,e,k,h, we get. 
   Å
Z
n
r
n
529 . 0
2
? ? 
 (iii) Calculation of velocity of electron 
 
2 / 1
2 2
,
2
?
?
?
?
?
?
?
?
? ?
mr
Ze
V
nh
ZK e
V
n n
?
;
1
8
sec .
10 188 . 2
?
?
? cm
n
Z
V
n
 
 (iv) Calculation of energy of electron in Bohr’s orbit 
 Total energy of electron = K.E. + P.E. of electron 
r
kZe
r
kZe
r
kZe
2 2
2 2 2
? ? ? ? 
 Substituting of r, gives us 
2 2
2 4 2 2
2
h n
k e mZ
E
? ?
? Where, n=1, 2, 
3………. ? 
 Putting the value of m, e, k, h, ? we get 
 atom per erg
n
Z
E
2
2
12
10 8 . 21 ? ? ?
?
 
    ) 10 1 10 8 . 21
7
2
2
19
erg J ( atom per J
n
Z
? ? ? ? ?
?
  ) 10 1.6 (1eV 6 . 13
19
2
2
J atom per eV
n
Z
E
-
? ? ? ? ? 
    mole cal k
n
Z
/ . 6 . 13
2
2
? ? ? (1 cal = 4.18J)  
 or 
1 2
2
1312
?
?
kJmol Z
n
 
 When an electron jumps from an outer orbit (higher energy) 
2
n to an inner orbit (lower energy) ,
1
n then the energy emitted in 
form of radiation is given by  
 
?
?
?
?
?
?
?
?
? ? ? ? ?
2
2
2
1
2
2 4 2 2
1 1 2
1 2
n n h
Z me k
E E E
n n
?
 
 atom eV
n n
Z E /
1 1
6 . 13
2
2
2
1
2
?
?
?
?
?
?
?
?
? ? ? ? 
 As we know that , ? h E ? ?? ? c and 
?
?
1
? ,
hc
E ?
?  
Page 5


Atomic Structure 
Rutherford's nuclear model 
Rutherford carried out experiment on the bombardment of 
thin (10
–4
 mm) Au foil with high speed positively charged ? ?
particles.  
He concluded that, an atom consists of  
(i) Nucleus which is small in size but carries the entire mass
i.e. contains all the neutrons and protons.
Properties of the nucleus 
(i) The small, heavy and positively charged portion of the
atom is known as nucleus. It is located at the centre of the
atom and discovered in 1911 by Ernest Rutherford.
(ii) Protons are positively charged particles.
(iii) Neutrons and protons are present in the nucleus hence
they are collectively known as nucleons.
Drawbacks of Rutherford's model 
(i)According to it “An electron moving around the nucleus
continuously loses its energy and should set up spiral motion 
 
ultimately failing into the nucleus”’. Hence this model does 
not able to explain how the moving electrons could remain 
in its orbit. 
 (ii) It does not able to explain the discontinuous spectrum and 
the line spectra of ? H atom. 
 Planck's quantum theory 
 According to this theory, the energy of each quanta is directly 
proportional to the frequency ( ? ) of the radiation, i.e. 
      Lets,  
 ? ? E or 
c hc
E hv;v Thus,E ? ? ?
??
 
 Where, h is proportionality constant also known as Planck’s 
constant. 
                                  h = 
34
6.626 10 Joulessec.
?
?
 or 
   6.626×10
–27
 erg sec.  
 
 Photoelectric effect 
 Einstein’s photoelectric effect equation  
 According to Einstein, 
 Maximum kinetic energy of the ejected electron = absorbed 
energy – threshold energy 
 
?
?
?
?
?
?
? ? ? ?
0
0
2
max
1 1
2
1
? ?
? ? hc h h mv 
 Where, 
0
? and 
0
? are threshold frequency and threshold 
wavelength. 
 
 
 Bohr’s atomic model 
 The Bohr postulates are, 
 (1) An atom consists of positively charged nucleus  
 (2) The electrons revolve around the nucleus in circular orbits  
 (3) The circular orbits are those for which the angular 
momentum of an electron is an integral multiple of ? 2 / h where 
h is the Planck’s constant. 
 
?
? ?
2
nh
mvr L ; 1 ? n , 2, 3, …… ? 
 Where L is the orbital angular momentum and n is the number 
of orbit.  
 (4) When electrons move in permitted discrete orbits they do 
not radiate or lose energy.  
 
 Advantages of Bohr’s theory  
 (i) Bohr’s theory satisfactorily explains the spectra of species 
having one electron, viz. hydrogen atom, 
? ? 2
, Li He etc.  
 (ii) Calculation of radius of Bohr’s orbit: According to Bohr, 
radius of  n
th
 orbit in which electron moves is 
Z
n
k me
h
r
n
2
2 2
2
.
4 ?
?
?
?
?
?
?
?
?
?
 
 Where, ? n Orbit number, ? m Mass number ? ?, 10 1 . 9
31
kg
?
? ? e Charge 
on the electron ? ?
19
10 6 . 1
?
? ? Z Atomic number of element, k = 
Coulombic constant ? ?
2 2 9
10 9
?
? c Nm 
 
 After putting the values of m,e,k,h, we get. 
   Å
Z
n
r
n
529 . 0
2
? ? 
 (iii) Calculation of velocity of electron 
 
2 / 1
2 2
,
2
?
?
?
?
?
?
?
?
? ?
mr
Ze
V
nh
ZK e
V
n n
?
;
1
8
sec .
10 188 . 2
?
?
? cm
n
Z
V
n
 
 (iv) Calculation of energy of electron in Bohr’s orbit 
 Total energy of electron = K.E. + P.E. of electron 
r
kZe
r
kZe
r
kZe
2 2
2 2 2
? ? ? ? 
 Substituting of r, gives us 
2 2
2 4 2 2
2
h n
k e mZ
E
? ?
? Where, n=1, 2, 
3………. ? 
 Putting the value of m, e, k, h, ? we get 
 atom per erg
n
Z
E
2
2
12
10 8 . 21 ? ? ?
?
 
    ) 10 1 10 8 . 21
7
2
2
19
erg J ( atom per J
n
Z
? ? ? ? ?
?
  ) 10 1.6 (1eV 6 . 13
19
2
2
J atom per eV
n
Z
E
-
? ? ? ? ? 
    mole cal k
n
Z
/ . 6 . 13
2
2
? ? ? (1 cal = 4.18J)  
 or 
1 2
2
1312
?
?
kJmol Z
n
 
 When an electron jumps from an outer orbit (higher energy) 
2
n to an inner orbit (lower energy) ,
1
n then the energy emitted in 
form of radiation is given by  
 
?
?
?
?
?
?
?
?
? ? ? ? ?
2
2
2
1
2
2 4 2 2
1 1 2
1 2
n n h
Z me k
E E E
n n
?
 
 atom eV
n n
Z E /
1 1
6 . 13
2
2
2
1
2
?
?
?
?
?
?
?
?
? ? ? ? 
 As we know that , ? h E ? ?? ? c and 
?
?
1
? ,
hc
E ?
?  
 
?
?
?
?
?
?
?
?
? ?
2
2
2
1
3
2 4 2 2
1 1 2
n n ch
Z me k ?
 
 This can be represented as 
?
?
?
?
?
?
?
?
? ? ?
2
2
2
1
2
1 1 1
n n
RZ ?
?
 
 Where, 
3
4 2 2
2
ch
me k
R
?
? ; R is known as Rydberg constant.  
 
 
Spectral series 
S.No. Spectral series Lies in the region Transition 
21
nn ? 
(1) Lymen series Ultraviolet region 
1
n1 ? , 
2
n 2,3,4.... ??
 
(2) Balmer series Visible region 
1
n2 ? , 
2
n 3,4,5.... ??
 
(3) Paschen series Infra red region n
1
 = 3, 
2
n 4,5,6.... ??