CBSE Class 11 Chemistry Structure of Atom Worksheet Set 05

Question. Define proton and neutron? 
Answer. 
Proton: The smallest and lightest positive ion was obtained from hydrogen. A proton is a particle with a positive charge that is in the nucleus of an atom.
Neutron: A neutron is a sub-atomic particle with no net electrostatic charge, with a very similar mass to a proton. Neutrons make up the nucleus, held together by the strong force

Question. What is cathode ray tube? 
Answer. Cathode ray tube is made of glass containing two thin pieces of metal electrodes sealed in it. The electrical discharge through the gases could be observed only at very low
pressure and at very high voltages. The pressure of different gases could be adjusted by the evacuation of the glass tubes.

Question. What are the major problems after the discovery of the sub atomic particles? 
Answer. The problems after the discovery of sub atomic particles are:
1. To account for the stability of atom.
2. To compare the behaviour of elements in terms of both physical and chemical properties.
3. To explain the formation of the different kinds of molecules by the combination of different atoms.
4. To understand the origin and nature of the characteristics of electromagnetic radiation absorbed or emitted by the atoms.

Question. What is an important feature of the Thomson model at atom? 
Answer. An important feature are:
1. An atom consists of a positively charged sphere and the electrons are embedded in it.
2. The negative and positive charges are equal in magnitude.
3. The atom as a whole is electrically neutral.
4. The mass of the atom is assumed to be uniformly distributed over the atom.

Question. What do you mean by the radioactivity and radioactive elements?
Answer. Radioactivity: Radioactivity is the spontaneous emission of radiation in the form of particles or high energy photons resulting from a nuclear reaction. Radioactive decay is a random or stochastic process that occurs at the level of individual atoms.
Radioactive elements: Radioactive elements are unstable isotopes that release
subatomic particles or energy as they decay. Alpha decay releases two protons and two neutrons.

Long Answer

Question. What are the characteristics of the positively charged particles? 
Answer. The characteristics of the positive charged particles are:
1. Unlike the cathode rays mass of the positively charged particles depends upon the nature of the gas present in the cathode ray tube. These are simply positively charged gaseous ions.
2. The charge to mass ratio of the particles depends on the gas from which these originate.
3. The behaviour of these particles in the magnetic or electric field are opposite to that observed for electron of cathode rays.
4. Some of the positively charged particles carry a multiple of the fundamental unit of the electrical charge.
5. Electric charge is a conserved property; the net charge of an isolated system, the amount of positive charge minus the amount of negative charge, cannot change.
6. An electric charge has an electric field, and if the charge is moving it also generates a magnetic field.

Question. Difference between isobars and isotopes? 
Answer. 1. Isobars are chemical elements having the same atomic mass whereas isotopes are different atomic structures of the same element.
2. Isobars have different chemical elements whereas isotopes have the same chemical element in the different forms.
3. In isobars physical properties are often similar whereas in isotopes physical properties are different from each other.
4. In isobars atomic numbers are different from each other whereas in isotopes atomic numbers are equal to each other.
5. In isobars atomic masses are equal to each other whereas in isotopes atomic masses are different from each other.
6. Isobars occur in different places in the periodic table whereas isotopes occur at same place in the periodic table.

Question. Explain what happens when a cathode ray tube is discharge tube perforated anode? 
Answer. When a cathode ray tube is discharge tube perforated anode are:
1. The cathode rays start from cathode and move towards the anode.
2. These rays themselves are not visible but their behaviour can be observed with the help of the certain kind of the material.
3. In the absence of the electrical or magnetic field these rays travel in the straight lines.
4. In the presence of the electrical or magnetic field the behaviour of the cathode rays are similar to that expected from negatively charged particles by suggesting that the cathode rays consist of negatively charged particles are called electrons.

Question. Difference between atomic number and mass number? 
Answer. 1. Atomic number is the number of the protons present in the atoms whereas mass number is the sum of the number of protons and the neutrons of an atom.
2. Atomic number has always a smaller value than the mass number whereas mass number has always a large value than the atomic number.
3. Atomic number not affected by number of neutrons whereas mass number is affected by the number of neutrons.
4. In atomic number isobars cannot have the same atomic number whereas in mass number isobars have the mass number.
5. In atomic number isotopes have the same atomic number whereas in mass number isotopes have different mass numbers.

Question. Explain the observation of the structure of atom and the observation of the nuclear model of atom? 
Answer. On the basis of the observation regarding the structure of an atom are:
1. Most of the space in the atom is empty as most of α- particles passed through the foil undeflected.
2. A few positively charged α- particles were deflected. The defection must be due to enormous repulsive force showing that the positive charge of the atom is not spread throughout the atom.
3. Calculations by the Rutherford showed that the volume occupied by the nucleus is negligibly small as compared to the total volume of the atom.
On the basis of the above observation and conclusions, Rutherford proposed the nuclear model of the atom. According to the model:
1. The positive charge and most of the mass of the atom was densely concentrated in extremely small regions, a very small portion of the atom is called nucleus by the Rutherford.
2. The nucleus is surrounded by the electrons that move around the nucleus with a very high speed in circular paths called orbits.
3. Electrons and the nucleus are held together by electrostatic forces of the attraction.