1st Year NotesChemistry class 11th

1st year Chemistry Chapter 3 The Atomic Structure

1st year Chemistry Chapter 3 The Atomic Structure Question an Answers

Short and Simple Question an Answer

Q.1: What are defects of Rutherford’s atomic model?

Ans: Rutherford’s atomic model are:
➤ It is based on the laws of the motion and the gravitation. These laws charged bodies like electrons.
➤ The revolving electron should emit the energy continuously and by producing a spiral path, it should ultimately fall into the nucleus. But actually the atoms don’t do.
The atom should go continuously spectra, but they give the line spectra.

Q.2: How does Bohr introduce the Plank’s Quantum Theory in hic model?

Ans: Bohr produced that electrons move around the nucleus in the fixed orbits with definite energies. Whenever, they change the orbits they eit or absorb the energy in terms of photons which was suggested by Planks.

Q.3: Indicate the limiting line of Balmer series?

Ans: When the electrons jumps from an infinite orbit to n = 2 of hydrogen atom then this line on the photographic plate is called the limiting line, it has energy and lies in the u.v region.

Q.4: How did Rutherford’s model of an atom first af all proved the existence of nucleus of the atom

Ans: Rutherford’s observed that most of the alpha particles passed straight through the gold foil without any deflection from the path. Few of them were deflected at some angles more than 900 and a few were deflected heavy and positively charged part at the center. This heavy part at the centre is called nucleus.

Q.5: Why the anode rays depend upon the nature of the gas?

Ans: 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 rays particle depends upon the nature of the gas, so the anode ray for all gaseous substances are different.

Q.6: The e/m value of positive rays for different gases are different? But those for cathode rays the elm value are same? Justify?

Ans: The nature of particles of positive rays in a discharge tube depend upon the nature of the gas because the nucleus of every gas has 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 elm values. In this case of cathode rays which are always electrons. E/m values remain the same.

Q.7: Define Hund’s Rule?

Ans: 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 spin.

Q.8: The magnetic quantum number gives us the orientation of orbital in space? Justify?

Ans: In order to designed the direction of p-sub shell, we need an additional quantum number and that is called magnetic quantum number. It tells us the orientation of orbital in space p sub shell has the orbitals and they have three directions in spacer For each there s a separate value of magnetic quantum number.

Q.9: What is the function of principle of quantum number?

Ans: This quantum number () give us the shape of the orbital.
When n = 0, the orbital is S
When n = 1, the orbital is P
When n = 2, the orbital is d
When n = 3, the orbital is f

Its value also determines the energy of electrons.

Q.10: Heisenberg’s uncertainly principle has no relation with Bohr’s Atomic model? Justify it?

Ans: 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 planer. It means that Bohr’s model is very simple as compared to Heisenberg’s uncertainly principle.

Q.11: Explain Cathode rays are material particles having definite mass and velocities?

Ans: Cathode rays are material particles having definite mass and velocity because they derive as small peddle wheel placed in their path.

Q.12: Describe continuous spectrum?

Ans: In this spectrum boundary line between the colours cannot be marked the colours and diffused into each other. It is obtained from sunlight or bulb light. Example of continuous spectrum is rainbow.

Q.13: Define atomic spectrum?

Ans: In this spectrum lines are separated by definite distance depending upon the nature of element.

Q.14: How are x-rays produced?

Ans: X-rays are produced when rapidly moving electron collide with heavy metal and in the discharge tube.

Q.15: Give the characteristics of Electrons, protons and neutrons?

It is a negatively charged particle.
Charge of electron is 1.6022 x 1019 coulombs.
Mass of electron is 0.00548597 a.m.u. Or 1.1 x 10¹³¹ kg.
Electron is represented by “e”. Electrons revolve around the nucleus of atom is different circular orbits.
Proton is a positively charged particle. Charge of proton is 1.6022 x 1019 coulombs.
Mass of proton is 1.0072766 a.m.u. Or 1.6726 x 1027 kg.
Proton is 1837 times heavier than an electron. Protons are present in the nucleus of atom.
It is a neutral particle because it has no charge.
Mass of neutron is 1.0086654 a.m.u. Or 1.6749 x 10-27 kg.
Neutron is 1842 times heavier than an electron.
Neutrons are present in the nucleus of an atom.

Q.16: How is wavelength of the electron related to momentum of electron?
Ans: Wavelength of electron is related to the momentum of electron on
y = h/mv
Am is the mass of particle
V is the velocity of electron
……is the De borglie’s wavelength.

Q.17: Cathode rays are deflected towards positively charged plate and cathode rays deflected towards negatively charged plate? Justify?

Ans: Cathode rays consist of negatively charged particles and anode rays consist of positively charged particles. Because opposite charges attract each other therefore cathode rays are deflected towards positively charged plate and anode rays are deflected towards negatively charged plate.

Q.18: Cathode rays produce shadow of an opaque object placed in their path? Explain?

Ans: Because cathode is material in nature and consists of streams of particles which are not pass through opaque and form shadow.

Q.19: Why the anode rays called canal rays?

Ans: Because anode rays pass through canals (opening/cuts into cathode) and they are called canal rays.

Q.20: Alpha rays have penetrating power than Beta rays?

Ans: Alpha rays have high penetrating power than beta rays due to being relatively heavy particles.

Q.21: Gamma rays have more penetrating power than alpha and beta rays? Justify?

Ans: Gamma rays have high penetrating power on account of high velocity and non – material nature.

Q.22: Beta have high velocity than alpha rays? Why?

Ans: Because alpha particles are heavier than beta particles.

Q.23: How positive rays are produced?

Ans: Positive rays are produced when high speed cathode rays strike with the molecules of a gas enclosed in the discharged tube.

Q.24: How the bending of the cathode rays in the electric and magnetic fields shows that they are negatively charged?

Ans: Cathode rays are deflected towards the positive plate when electric field applied. It shows that cathode rays are negatively charged. When cathode rays are passed through the magnetic field, they bend perpendicularly to the joining line of two poles.
This is due to the negative charge. Anyhow, positively charged particles will bend in opposite direction to that of electrons.

Q.25: Why is it necessary to decrease the pressure in the discharge tube to get the cathode rays?

Ans: The pressure in discharge tube is decreased to allow the cathode rays and anode rays to move freely from one electrons to other. In this way, the possibility of collisions between rays and the molecules are minimized.

Q.26: Why the cathode rays are produced in the discharge tube by applying a high voltage?

Ans: 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.

Q.27: Why elm value of the cathode rays is just equal to that of electron?

Ans: Since cathode rays are electrons, so their elm values are just equal to those of electrons.

Q.28: Which observations tell the presence of cathode rays in the discharge tube?

Ans: Cathode rays produced in the discharge tube fall upon the surface of the glass tube, just opposite to the cathode surface giving fluorescence. Fluorescence has different colours, which depends upon the nature of the glass tube.

Q.29: Flow mass of au element is calculated from elm and charge?

Ans: Mass of electron is calculated by using e/m value and charge of electron from Millikan oil chop experiment as:
e/m = 1.7588 x 10¹¹ coulomb Kg”¹
e = 1.6022 x 1019 coulombs

Q.30: State Pauli’s exclusion iple and Hunds rule?

Ans: According to Pauli principle no two electrons in an atom can have the same set of four quantum numbers. According to the Hund’s rule, if degenerate orbitals are available and more than two electrons are to be placed in them, then place in separate orbitals with the same spins rather than in the same orbital with the opposite spins.

Q.31: Give the properties of neutron?

➤ Neutron is electrically neutral particles.
➤ The mass of a neutron is almost the same as the mass of a proton.
➤ Mass of a neutron = 1.0087 a.m.u. or 1.6750 x 1027 kg.
➤ A free neutron decays into a proton with the emission of an electron and neutron.
➤ They can not ionize gases.
➤ They are highly penetrating particles.
➤ They can expel high speed protons from paraffin, water, paper and cellulose.
➤ Fast and slow neutrons.
➤ Neutrons are used as projectiles.
➤ When slow moving neutrons hit the Cu metal, radioactive Cu is produced along with the emission of Gamma Rays.

Q.32: Give the properties of a, ß, y rays?

➤ α – rays consist of a particle. Each a particle consists of ₂He nucleus.
➤ α- particle carry positive charge. Mass of each a particle is 4 times that o or H-atom.lonization power of a rays is very high.
➤ Penetration power of a rays is very small.
➤ α-rays produce fluorescence in different substances. a rays produce burn and source on human body.
➤ α-rays can produce artificial radioactivity in certain nuclei.
➤ They have strong ionization power because they remove electrons from the atoms of gas through which they pass. Blogspot.com
➤ Their velocity range is 3 x 10′ m/s to 3 x 10 m/s
➤ ẞ-rays consist of fast moving electrons,
➤ ẞ-rays have negative charge.
➤ Velocity of ẞ-rays is from 9 x 10′ m/sec to 27 x 10′ m/sec.
➤ ẞ-rays affect the photographic plate.
➤ lonization power of ẞ-rays is very small.
➤ Kinetic energy of ẞ-rays is less than that of a – rays.
➤ ẞ-rays produce fluorescence in different substance.
➤ y-rays are electromagnetic radiations.
➤ y-rays have no charge.
➤ y-rays travel with the velocity of light that is 3 x 108 m/sec.
➤ Penetration power of y-rays is very large. It is about hundred times larger than that of B-rays.
➤ y-rays produce feeble fluorescence when incident on screen coated with barium platino cyanide.

Q.33: Give the properties of Cathode Rays?

➤ These rays originate from cathode.
➤ Cathode rays travel in straight line.
➤ Cathode rays exert mechanical pressure.
➤ The cathode rays consist of material particles because they produce shadow of objects placed in the way.
➤ Cathode rays deflect in electric field towards the positive terminal.
➤ Cathode rays deflected by magnetic field.
➤ Cathode rays penetrate small thickness of matter such as alumimium foil, gold foil etc.
➤ These rays carry a negative charge.

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