11th Class Chemistry Chapter 5 Atomic Structure Short Question Answers

 

11th Class Chemistry Chapter 5 Atomic Structure Short Question Answers Below

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1.Which observations tell the presence of cathode rays in the discharge tube?
Cathode rays produced in the discharge tube fall upon fluorescence. Fluorescence has different colors which depends upon the nature of the glass tube.
2.Why the cathode rays are produced in the discharge tube by applying a high voltage?
When the voltage of 5000-10000 volts is applied at the pressure of around 0,01 torr then a glow appears and cathode rays travel from cathode towards the anode in the discharge tube. High voltage is necessary to break the molecules of the gas into atoms and to remove the electrons from outermost orbitals.
3.How various experiments conducted in the cathode ray tube show that cathode rays are material particles with the negative charge on them?
Cathode rays rotate a pin wheel. The vans of the pin wheel get the momentum from the particles of the cathode rays and get the movement. When these rays are passes through the electrical field they are deflected towards the positive plate.
4.Why is it necessary to decrease the pressure in the discharge tube to get the cathode rays?
The pressure in discharged tube is decreased to allow the cathode rays to move freely from one electrode to the other. In this way the possibility of collisions between rays and the gas molecules are minimized.
5.Whichever gas is used in the discharge tube the nature of the cathode rays remains the same. Why?
All the gases are consisted of atoms molecules. They have electrons in outermost orbitals. These electrons are detached by the high voltage and due to collisions these electrons become free. They are repelled by the cathode and attracted towards the anode. That is why they are called cathode rays. They are always electrons and nothing else.
6.Why e/m value of the cathode rays is just equal to that of electron?
Since cathode rays are electrons so their e/m values are just equal to those of electrons.
7.How the bending of the cathode rays in the electric and magnetic fields shows that they are negatively charged?
Cathode rays are deflected towards the positive plate when electric field is applied. It shows that cathode rays are negatively charged. When cathode rays are passed through the magnetic field they bend perpendicular to the negative charge. Anyhow positively charged particles will bend in opposite direction to that of electrons in the magnetic field.
8.Why the positive rays are also called canal rays? Give its reason?
They are detected by allowing them to pass through the canals of cathode. These canals are the holes in the cathode material.
9.The e/m values of positive rays for different gases are different but those for cathode rays the e/m values are same.justify it?
The nature of particles of positive rays in a discharge tube depend upon the nature of the gas because the nucleus of every gas its own number of protons and neutrons.Greater the number of protons and neutrons in the nucleus of an atom or nuclei of the molecule smaller the e/m values.In the case of cathode rays which are always electrons e/m values remain the same.
The e/m values of positive rays obtained from hydrogen gas is 1836 times less than that of cathode rays.Justify it?
When we use hydrogen gas in the discharge tube the positive rays are consisted of single protons.In cathode rays each ion is consisted of electrons.The proton is 1836 times heavier than of electron.So e/m value of proton is 1836 times smaller than that of electron.
11.Why the anode rays depend upon the nature of the gas?
Anode rays are those particles which are consisted of rest of the atom or molecule after the removal of one electron.The mass of every anode ray particle depends upon the nature of the gas.so the anode rays for all gaseous substances are different.
12.How the idea of the proton can be verified by taking H2 gas in the discharge tube?
In the discharge tube the molecules of H2 are broken up into hydrogen atoms.These hydrogen atoms are deprived of their electrons and the nucleus consisted of one proton acts as particle of anode ray.In this way if we study the anode rays they give the properties of the protons.
13.How the slow neutrons prove to be more effective than the fast neutrons?
When the traveling neutrons have energy below one electron volt then they are called slow neutrons.They are more effective in fission processes.Slow neutrons hit the copper metal and radiations are emitted giving us a new isotope of copper i.e.6629Cu which is again radioactive.
on1+6629Cu………………. 6629Cu+hv   (radiations)
6629Cu……………………..6630Zn+1eo
14.How did Rutherford’s model of an atom first of all proved the existence of nucleus of the atom?
Rutherford observed that most of the a-particles passed straight through the gold foil without any deflection from the path.Few of them were deflected at some angle more than 90ᵒ and a few were deflected back on the original path.He concluded that the atom contains heavy and positively charged part at the center.This heavy part at the center is called nucleus.
15.What are the defects of Rutherford’s atomic model?
It is based on the laws of the motion and the gravitation.These laws are not for the charged bodies like electrons.The revolving electron a spiral path it should ultimately fall into the nucleus.But actually the atoms don’t do it.The atom should give continuously spectra but they give the line spectra.
16.How does Bohr introduce the Planck’s quantum theory in his model?Give its two postulates?
Bohr proposed that electrons move around the nucleus in the fixed orbits with definite energies.Whenever they change the orbits they emit or absorb the energy in terms of photons which was suggested by Planck in 1900.The electron revolves around the nucleus in circular way.The electron in same orbit keeps the energy constant.
17.How do you justify that the distances between adjacent orbits of H atom go on increasing from lower to the higher orbits?
In the equation for the radius of the H-atom after putting the values of different parameters for H-atom is as follows
r =  0.529 (n2)Aᵒ                        1 Aᵒ = 10-10m
If we put the value of ‘n’ = 1,2,3,,,,,,,,,,,,we can get the radii which show that the distances between adjacent orbits go on increasing.
r1 = 0.529 Aᵒ
r2 = 2.14 Aᵒ
r3 = 4.7 Aᵒ
r4 = 8.4 Aᵒ
18.How do you justify that of orbit in H-atom is directly proportional to the square of number of orbit?
19.How do you justify that radius of orbit in H-atom is inversely proportional to the number of protons in the nucleus?
According to the above equation radius is inversely proportional to the number of protons in the nucleus.Greater the number of protons smaller the radius i.e.He+ion is smaller than that of hydrogen atom.
20.Energy of an electron is inversely proportional to ‘n2’ but energy of higher orbits are always greater than those of the lower orbits.Why?
21.The energy difference between adjacent levels goes on decreasing sharply.Why?
If we put value of n as 1,2,3,4, we get the energies of various orbits of hydrogen atom.These values are as follows:
E1 = -2.18×10-18j
E2    = -0.54×10-18j
E3   = -0.24×10-18j
E4  = -0.14×10-18j
So E1 – E1> E3– E2> E4– E3…………. and so on.
As is clear from these values that energy differences between adjacent levels go on decreasing from lower to the higher levels.
22.Justify that the distance gaps between different orbits go on increasing from the lower to the higher orbits?
23.How does Bohr’s equation give us the wave number of photon which is emitted or absorbed during jumping of electron between two orbits?
24.Hydrogen atom and He+ are monoelectronic system but the size of He+ is much smaller than H.Why?
25.Do you think that the size of Li+2 is even smaller than He+?justify with calculations.
26.What are defects of Bohr’s atomic model?
It is only applicable to hydrogen atom,He+,Li+2,and Be+3 to understand their spectra it cannot explain the fine structure of hydrogen atom.The explanations of zeeman effect and Stark effects are also not available from this model.
27.Why does the fine structure of H-atom in its spectrum finds no explanation from Bohr’s model?
When the spectroscopes of high resolving powers were used then some new lines were also recorded on the photographic plate for H-atom.These lines were very weak.The appearance of the weak lines was called the fine structure of H-atom.Bohr could not find any quantum number to justify these fine lines.
28.What is Zeeman effect?
When the light of spectral lines is passed through the magnetic field then the one spectral line is splatted up into many spectra lines.This splitting of the spectral line cannot be explained by bohr’s theory.
29.What is Starch effect?
When the light of spectral lines is passed through the electrical field then the one spectral line is split up into many spectra lines.This splitting of the spectral line cannot be explained by Bohr’s theory.
30.What is line spectra of hydrogen and how it differs from continuous spectrum?
Hydrogen absorbs certain photons of light to promote the electron from its lower energy level to high energy levels.These photons do not reach the topographic plate so line spectra is obtained.The spectra of ordinary light is continuous because all the photons reach the photographic plate and no frequency is absorbed on its way.
31.The energy associated with the violet is greater than the red color in the visible region of spectra.Why?
The photons of violet color bend t maximum extent after passing through the prism and their range of wavelength is from 400-420 nm.They have high energy and have shorter wavelengths.The photons of the red color have the longer wavelength ranging from 630 to 800 nm.These photons bend in the prism to lesser extent.
32.Why the photographic plate is white and few dark lines are there in the line absorption spectra of a substance?
Some of the photons are absorbed by the sample to excite the eletrons of a substance from lower energy levels to higher energy levels.These photons of light don’t reach the photographic plate.Rest of the light reaches the photographic plate,so the plate is white.Only those places are dark in the form of sharp lines where the photon don’t reach.
33.Why the photographic plate is dark and a few bright lines are there in the line emission spectra of hydrogen?
The sample of hydrogen is taken in a glass tube.Electric current is passed through the gas.Electrons of the atoms or molecules are excited to higher energy levels.These electrons fall back to the original levels and emit the photons of light.These emitted photons produce bright lines and rest of the plate is dark.
34.How Bohr’s model justifies the H-spectra?
Lyman and Balmer discovered spectra of hydrogen in 1887.They did know that reasons for their line.In 1913 Bohr’s equation of v gives us the values of wave number as were measured by Lyman Balmer Pashen Bracket and Pfund.So Bohr’s model can explain the spectra of hydrogen.
35.What is Ha – line in hydrogen spectrum?
This is the first line of Blamer series.It is produced due to the jumping of electrons from n =3 to n=2.This line in the visible region.This line was noted experimentally in 1887 but got its justification on theoretical basis in 1913 by Bohr.
36.Indicate the limiting line of Balmer series?
When the electrons jump from an infinite orbit (n=oo) to n = 2 of hydrogen atom then this line on the photographic plate is called the limiting line.It has high energy and lies in the visible resin.
37.How is atomic emission spectrum obtained?
The substance is grated in a glass tube by the electrical spar.The electrons are excited to higher energy levels and when they come back they emit the photons of light.These emitted photons are recorded on the photographic plate.The whole plate is dark along with the few bright lines.The collection of these bright lines is called line emission spectrum of the substance.
38.The x-rays produced in a discharge tube experiment are characteristic of the target metal.How?
The wavelength of the x-ray which are emitted from the surface of the metal depend upon the atomic number of the metal.Greater the number of protons in the nucleus of metal atom greater the forces of attraction for the inner electrons.Greater the energy differences smaller the wavelength of x-rays.X-rays are emitted due to jumping of electrons from higher levels to n = 1 the vacant level.
39.What is Moseley’s Law?
Moseley’s law is the relationship between the frequency of a line of spectrum of x-rays with the atomic number of the target metal.
40.How the idea of dual nature of matter was deduced from the dual nature of light?
41.According to de-Broglie’s idea only microscopic particles have the waves.How waves were measured?
Keeping in view de-Broglie’s equation for dual nature of matter the wavelength is inversely proportional to the mass of the particle.
h =H/mv
For a stone of 100gm moving with the velocity 10 ms-1 the wavelength associated with that is 6.65 ×10-30m.This wavelength cannot be measured by any instrument.In the case of electron moving with the velocity of 6×10+5 ms-1 the wavelength associated with that is 1.1 nm which can be easily measured by the instrument.Davisson and German devised an experiment in which electrons of cathode rays were thrown on Ni-crystal and diffraction was studied.
42.What are the basis of Schrodinger wave equation?
(i) Electron behaves like a wave. (ii) Heisenberg’s uncertainty principle is obeyed. (iii)We can only talk about the probability of electron
43.Heisenberg’s uncertainty principle has no relation with Bohr’s atomic model.justify it?
Since the electron has wavy nature and paths are elliptical as well so the simultaneous determination of position and momentum is not possible.But Bohr’s model does not accommodate the wavy nature of electron.He says that the paths are fixed orbits and their orbits are planar.It means that Bohr’s model is very simple as compared to Heisenberg’s uncertainty principle.
44.What is the function of principal quantum number?
Its values are whole number and never zero negative or fractional.It gives us information about: (i)Energy of electron. (ii)Distance of electron from the nucleus.
45.What is the function of azimuthal quantum number?
This quantum number(/) gives us the shape of the orbital.
For   / = 0,   s-orbital
/  =  1,   p-orbital
/   =  2,   d- orbital
/    = 3,    f- orbital
Its value also determine the energy of electron.When I = 3,then m has ±3,±2,±1 0 values.
46.The magnetic quantum number gives us the orientation of orbital in space.Justify it?
In order to designate the directions of p-orbitals in p- subshell,we need an additional quantum number and that is called magnetic quantum number.It tells us the orientation of orbital in space. P- subshell has three orbitals and they have three directions in space.For each direction there is a separate value of magnetic quantum number.
47.Define Hund’s rule?
This rule is concerned with the distribution of electrons in degenerate orbitals.These orbitals may be atomic or molecular.According to this rule if degenerate orbitals are available and more than one electrons are to be placed in them then place them in separate orbitals with the same spin rather than putting them in the same orbital with opposite spins
48.Define atomic number?Write the electronic configuration of oxygen?
Oxygen has eight electrons and has the electronic configuration as follows:
8O = 1s 2s 2p×2py 2pz.
49.State pauli’s exclusion principal and hund’s rule?
According to pauli’s principal no two electrons in an atom can have the same set of four quantum numbers.According to hund’s rule if degenerate orbitals are available and more than two electrons are to be place in  then place them in separate orbitals with the same spins rather than in the same orbital with the opposite spins.
50.What will be the position of electron in an atom when (n+I) value is same for two sub-shells?
The electron will be accommodated in that orbital whose ‘n’ value is smaller.

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