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Published on: 27/07/2018
The chapter Structure of Atom contains the important question in CBSE 11th Standard chemistry. It covers one mark, two, three and five marks questions from the book back and PTA question.
Download CBSE Class 11th Standard CBSE Chemistry question papers, sample papers, important questions, and previous year solved papers in PDF format. Get free study materials, NCERT solutions, and exam preparation resources for Class 11th Standard CBSE Chemistry
Questions + Answers key
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1.
Write the electronic configuration of \({ 9 }^{ { F }^{ 19 } },{ 16 }^{ { S }^{ 32 } }and \ { 18 }^{ { Ar }^{ 38 } }\)and then point out the element with A maximum number of unpaired electrons.
2.
Which atoms are indicated by the following configuration?
a) [He]2s1
b) [Ne] 3s23p3
c) [Ar]4s23d1
3.
The velocity associated with a proton moving in a potential difference of 1000 V is 4.37 × 105 ms–1. If the hockey ball of mass 0.1 kg is moving with this velocity, calcualte the wavelength associated with this velocity.
4.
What must be the velocity of a beam of electrons if they are to be display a de-Broglie wavelength of \(100\overset { \circ }{ A } \) (mass of electron)
= \(9.1\times { 10 }^{ -31 }kg,h=6.6\times { 10 }^{ -34 }Js\)?
5.
Calculate the energy associated with the first orbit of He+. What is the radius of this orbit?
6.
Calculate wave number of the line having frequency 5 x 1016 Hz.
7.
What kind of information about an electron in an atom is obtained from its wave function?
8.
How long would it take a radio wave of frequency, 6 x 103 s-1 to travel from Mars to the Earth, a distance of 8 x 107 km?
9.
How does the Bohr theory of the hydrogen atom differ from that of schrodinger?
10.
Lifetimes of the molecules in the excited states are often measured by using pulsed radiation source of duration nearly in the nano second range. If the radiation source has the duration of 2 ns and the number of photons emitted during the pulse source is 2.5 × 1015, calculate the energy of the source.
11.
Calculate energy of one mole of photons of radiation whose frequency is 5 x 1014 HZ.
12.
Can we apply Heisenberg's uncertainty principle to a stationary electron? why or why not?
13.
Why did Heisenberg replace the concept of definite orbits by the concept of probability?
14.
Why are Bohr's orbits called stationary states?
15.
What is the experimental evidence in support of the idea that electronic energies in an atom are quantised?
16.
What do you mean by saying that energy of the electron is quantised?
17.
An atom having atomic mass number 13 has 7 neutrons. What is the atomic number of the atom?
18.
What is the difference between atomic mass and mass number?
19.
Which of the following will not show deflection from the path on passing through an electric field? Proton, cathode rays, electron, neutron
20.
What is the difference in the origin of cathode rays and anode rays?
21.
Calculate the frequency, energy, and wavelength of radiation corresponding to the spectral line of lowest frequency in Lyman series in the spectra of hydrogen atom. Also, calculate the energy for the corresponding line in the spectra of Li2+. (R = 1.09678 x 107 m-1 , c = 3 x 10 8 ms-1 , h = 6.625 x 10-34 Js).
v = 2.47 x 1015 s-1 , \(\lambda \) = 121.6 nm
22.
How many electrons in an atom may have the following quantum numbers?
(a) n = 4, ms = – ½
(b) n = 3, l = 0
1.
\({ 9 }^{ { F }^{ 19 } }={ 1s }^{ 2 }{ 2s }^{ 2 }{ 2p }_{ x }^{ 2 }{ 2p }_{ y }^{ 2 }{ 2p }_{ z }^{ 1 }\)
\({ 16 }^{ { S }^{ 32 } }={ 1s }^{ 2 }{ 2s }^{ 2 }{ 2p }^{ 6 }{ 3s }^{ 2 }{ 3p }_{ x }^{ 2 }{ 3p }_{ y }^{ 1 }{ 3p }_{ z }^{ 1 }\)
\( { 18 }^{ { Ar }^{ 38 } }={ 1s }^{ 2 }{ 2s }^{ 2 }{ 2p }^{ 6 }{ 3s }^{ 2 }{ 3p }^{ 6 }\)
Maximum number of unpaired electrons = 2 in\({ 16 }^{ { S }^{ 32 } }\)
2.
a) [He]2s1 represents 3Li (lithium)
b) [Ne] 3s23p3 represents 15P (phosphorus)
c) [Ar]4s23d1 represent 21Sc (scandium)
3.
Given velocity of proton = 4.37 x 105 m sec-1
potential difference = 1000v
Mass of hockey ball = 0.1 kg
Wavelength associated with the velocity of hockey ball
\(\lambda =\frac { h }{ mv } \)
\(= \frac { 6.626\times 10^{ -34 }\ kg\ m^{ 2 }\ s^{ -1 } }{ 0.1kg\times 4.37\times 10^{ 5 }m\ s^{ -1 } }\)
\(=15.16\times10^{ -39 } \ m=1.56\times10^{ -38 }\ m\)
4.
\( \lambda=\frac{h}{m v} \)
\( \text { or } v=\frac{h}{m \lambda} \)
\( =\frac{6.63 \times 10^{-34} \mathrm{kgm}^2 \mathrm{~s}^{-1}}{\left(9.1 \times 10^{-31} \mathrm{~kg}\right) \times\left(100 \times 10^{-10} \mathrm{~m}\right)} \)
\( =7.28 \times 10^4 \mathrm{~ms}^{-1} .
\)
5.
En= \(\frac { \left( -2.18\times10^{ -18 }J \right) Z^{ 2 } }{ \left( n \right) ^{ 2 } } \) atom-1
For He+, n = 1, Z = 2
\(E_{ 1 }\frac { \left( -2.18\times10^{ -18 }J \right) Z^{ 2 } }{ \left( 1 \right) ^{ 2 } } =-8.72\times10^{ -18 }J\\ \)
The radius of the orbit is given by rn = \(\frac{52.9 (n^2)}{Z} pm\)
rn= \(\frac { \left( 0.0529nm \right) n^{ 2 } }{ Z } \)
Since, n = 1 and Z = 2
rn= \(\frac { \left( 0.0529nm \right) 1^{ 2 } }{ Z } =0.02645 \ nm\)
6.
1.67 x 108 m-1
7.
The square of the amplitude of the electron wave i.e \(\Psi ^{ 2 }\) at any point gives probability of finding an electron at that point.since, the region around the nucleus which represents the electron density at different points is called an orbits, hence the wave function for an electron in an atom is called orbital wave function.
8.
All radiations in vacuum travel with the same speed, i.e. 3 x 108 ms-1
Distance to be travelled from Mars to the Earth
= 8 x 107 km = 8 x 107 x 103 m(1 km = 103m)
Time Taken = \(\frac { 8\times { 10 }^{ 7 }\times { 10 }^{ 3 } }{ 3\times { 10 }^{ 8 } } =2.66\times { 10 }^{ 2 }s=4min43s\)
9.
Bohr's theory does not consider the de-Broglie concept of dual nature of electron and also contradicts with the Heisenberg's uncertaintly priciple , while the schrodinger equation is based on quantum mechanics while deals with the microscopic objects having both the particle as well as wave like character.
10.
Ferquency, V = \(\frac { 1 }{ Period } \)= \(\frac { 1 }{ 2\ ns } \) = \(\frac { 1 }{ 2\times 10^{ -9 }s } \)
= 0.5 x 109s-1
Energy of the source = Energy of 1 photon x number of photons produced
Esource = hv x N
= 6.626 x 10-34 Js x 0.5 x 109 s-1 x 2.5 x 1015
= 8.28 x 10-10 J
11.
Energy (E) of one photon is given by E = hv
h = 6.626 x 10-34 Js.
v = 5 x 1014 s-1 (given)
E = (6.626 x 10-34 Js) x (5 x 1014s-1) = 3.313 x 10-19 J
Energy of one mole of photons
= (3.313 x 10-19 J) x (6.022 x 1023mol-1) = 199.51 KJ mol-1
12.
No because velocity = 0 and thus, position can be measured accurately.
13.
This is because according to Heisenberg, the position of a microscopic particle like electron cannot be determined with certainity.
14.
This is because the energies of the orbits in which the electrons revolve are fixed.
15.
The line spectrum of any element has lines corresponding to definite wavelengths. Lines are obtained as a result of electronic transitions between the energy levels. Hence, the electrons in these levels have fixed energy, i.e quantised values.
16.
This means that the electrons in an atom have only definite values of energies.
17.
As A = n + p
p = A - n = 13 - 7 = 6
Hence, atomic number, z = p = 6
18.
Mass number is a whole number because it is the sum of the number of protons and number of neutrons whereas atomic mass is fractional because it is the average relative mass.
19.
Neutron is a neutral practice. Hence it will not be deflected on passing through an electric field.
20.
Cathode rays originate from the cathode whereas anode rays are not obtained from the anode. They are produced from the gaseous atoms by knock out of the electrone with high speed cathode rays.
21.
To find the wavelength of the emitted light, we use the following formula:
\(\dfrac{1}{\lambda } = R\left[ {\dfrac{1}{{n_1^2}} - \dfrac{1}{{n_2^2}}} \right]{Z^2}\)
Where λ is the wavelength, RH is the Rydberg constant, n1 and n2 are the lower and upper orbits involved in transition respectively and Z is the atomic number of the species.
For lowest frequency in the Lyman series in the hydrogen atom spectrum, n1 = 1 and n2 = 2. Substituting the rest of the values, \({R_H} = 1.09677 \times {10^7}{m^{ - 1}}\) and [Z = 1], we get:
\(\dfrac{1}{\lambda } = 1.09677\left[ {\dfrac{1}{{1_{}^2}} - \dfrac{1}{{{2^2}}}} \right]{1^2}\)
On simplifying, we get:
\(\dfrac{1}{\lambda } = 1.097 \times {10^7}\left( {\dfrac{3}{4}} \right) = 0.82275 \times {10^7}{m^{ - 1}}\)
Therefore, wavelength
\(\lambda = \dfrac{1}{{0.82275 \times {{10}^7}}} = 1.216 \times {10^{ - 7}}m\)
Simplifying further, we get:
\( \Rightarrow \lambda = 121.6 \times {10^{ - 9}}m = 121.6nm\)
As we know, \(\nu = \dfrac{c}{\lambda }\)
Where v is the frequency and x is the speed of light
\(\Rightarrow \nu = \dfrac{{3 \times {{10}^8}m{s^{ - 1}}}}{{121.6 \times {{10}^{ - 9}}m}}\)
On simplifying, we get:
ν=2.46 × 1015s−1
For finding energy, we use the formula E=h/cλ
Where E is the energy and hℎ is the Planck’s constant
\(\Rightarrow E=\frac{6.626 \times 10^{-34} \times 3 \times 10^8}{121.6 \times 10^{-9}}\)
On solving, we get \(E=16.3 \times 10^{-19} \mathrm{~J}\)
As we can see from our first equation, \(\frac{1}{\lambda} \propto Z^2\)
\(\Rightarrow \lambda \propto \frac{1}{Z^2}\)
Therefore, to get the wavelength of the spectral line of \(\mathrm{Li}^{2+}\) we just need to divide the wavelength of hydrogen atom with the square of the atomic number of Lithium (3)
\(\lambda_{L i}=\frac{121.6}{3^2} n m=13.55 n m\)
Therefore, energy of this transition:
\(E=\frac{h c}{\lambda_{L i}} \Rightarrow E=\frac{6.626 \times 10^{-34} \times 3 \times 10^8}{13.55 \times 10^{-9}}\)
On solving, we get:
\(E=146.7 \times 10^{-19} \mathrm{~J}\)
22.
(i) Total electrons if n = 4 = \(2n^{2}\),2 x \(4^{2}=32\)
half of the total electrons,i.e 16 electrons have ms = – ½
(ii) n = 3, l = 0 it is 3s-orbital and it can have two electron.
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