ADDITIONAL QUESTIONS AND ANSWERS:
1) What are isobars.
Ans: Isobars are the atoms of different having same atomic mass and different atomic numbers.
2) Write some difference between: a) Neutron and Electron b) Proton and electron c) Proton and Neutron d) Isotopes and Isobars
Ans:
| Neutron | Electron |
| i) Neutron is in the Nucleus | i) Electron revolves around the nucleus. |
| ii) Neutron has no charge | ii) Electron has negative charge |
| iii) The mass of a neutron is l u. | iii) An electron has negligible mass |
| Proton | Electron |
| i) Proton is in the nucleus | i) Electron revolves around the nucleus |
| ii) Proton has positive charge | ii) Electron has negative charge |
| iii) The mass of a proton is l u | iii) An electron has negligible mass |
| Proton | Neutron |
| i) Proton has positive charge | i) Neutron has no charge. It is neutral |
| ii) Increase in protons increases both atomic number and mass number | ii) Increase in neutrons increases only the mass number |
| Isotopes | Isobars |
| i) Isotopes are the atoms of same element having same atomic number but different atomic mass | i) Isobars are the atoms of different element same having same atomic mass but different atomic number |
| ii) Isotopes have identical chemical properties | ii) lsobars have different chemical properties |
3) 238 92 U is an isotope of uranium.
a) State its atomic number and mass number
Ans. Its atomic number 18 mass number 238.
4) Calculate the number ot protons and neutrons in the atom
Ans: Atomic number of uranium is 92, hence the number of protons is 92.
Mass number = protons + neutron is = 238.
No of neutrons = 238 − 92 = 146.
5) The isotopes of an element have the same chemical properties.
Ans.The isotope of an element only differ in the number of neutrons of their nuclei. They have the same number of protons and electrons.The electrons in the outermost shell that decides the valency or the combining capacity of an element, remains the same in all isotopes of an element. Therefore isotopes have same chemical properties
5) Atomic number of an element Y is 13, A. State the electronic configuration of Y.What is its valency Justify your answer.
Ans. 2, 8, 3. The valency is 3 because it can lose 3 electrons in the outermost orbit.
6) In the following table alphabets are written in blank spaces. Write correct values/ words for each of these alphabet.
Ans:
| Atomic Number | Mass Number | Number of Protons | Number of Neutrons |
| 7 | 14 | a | a |
| c | d | 12 | 12 |
Ans. a = 7 neutrons, b = 7 Protons, c = atomic number 11, d = mass number 23
7) Name any two isobars.
Ans: Calcium and Argon
8) One element having no neutron in its atom.
Ans: Hydrogen
9) The scientist who identified an electron.
Ans: J J Thompson.
10) Postulates at Thomson’s model of an atom.
Ans: (i) Atom consists of a positively charged sphere with electrons embedded in it.
(ii) Negative and positive charge are equal in magnitude.
11) Features of Rutherford s nuclear model.
Ans.(i) There is positively charged centre called a nucleus in an atom.
(ii) Electrons revolve around the nucleus in well-defined orbits iii) the size of the nucleus is very small as compared to the size of the atoms.
12) Bohrs postulates about the electrons revolving around the nucleus
Ans: Only certain special orbits known as discrete orbits are allowed inside the atom. Electron do not radiate energy while revolving in the discrete orbit.
13) The distribution of electrons in various shells of chlorine atom (Z=17)
Ans: K shell = 2 L Shell = 8 M shell = 7
14) The uses of isotope
Ans: The isotope of uranium is used in nuclear reactor. The isotope of cobalt is used in the treatment of cancer. The isotope of iodine is used the treatment of goitre.
15) The uses of isotopes in medicine.
Ans: The isotope of cobalt is used in the treatment of cancer. The isotope of iodine is used the treatment of goitre.
16) The mass and charge of an alpha particle.
Ans. Mass= 4u and charge = 2+
17) Neon is an inert gas. Justify with reference to its electronic configuration
Ans: Neon has eight electrons n the outermost orbit. Hence there is no tendency to gain, share or lose electrons.Therefore it is inert.
18) Why is the mass number of chlorine not a whole number
Ans: Chlorine occurs in nature in two isotopic forms with masses 35 u and 37 u. Their ratio is 3:1.The average mass of all the naturally occurring atoms works out to be 35.5. Hence the mass number of chlorine is 35.5
19) What are isotopes
Ans: Isotopes are the atoms of the same element having same atomic number but different atomic numbers.
20) Ozone is not an isotope of Oxygen. Justify
Ans: Ozone consists of three atoms of oxygen. Individual atoms of ordinary Oxygen and Ozone are identical, they do not differ in their atomic masses. Therefore Ozone is not an isotope of Oxygen.
21. Which sub-atomic particles of an atom are responsible for atomic mass ?
Ans : Neutrons and Protons are responsible for atomic mass .
22. Helium electron has 2 electrons in its valence shell but its valency is not 2 . Explain .
Ans : Its valency is zero because its first shell is the outermost shell which is complete . It cannot lose or gain or share electrons .
23. What is a proton ? Who discovered it ?
Ans : Proton is positively charged particle present in nucleus . It was discovered by Goldstein .
24. In which of the rays e/m ratio is constant ?
Ans : Cathode rays e/m ratio is constant .
25. What are the maximum number of electrons that can be accommodated in outermost shell of an atom ?
Ans : The maximum number of electrons which can be present in outermost shell is 8 .
26. Atomic number of an element is 16 . What is its valency ?
Ans : Its valency is 2 because its electronic configuration is 2 , 8 , 6 . It can gain 2 electrons to become stable .
27. Why are the shells in which electrons revolve called energy levels ?
Ans : It is because each shell is associated with fixed amount of energy , therefore , they are called energy levels .
28. One electron is present in the outermost shell of the atom of an element X . What would be the nature and value of charge on the ion formed if this electron is removed from the outermost shell ?
Ans : It will acquire positive charge and value will be equal to +1 .
29. Define valency .
Ans : Valency is defined as the number of electrons lost or gained or shared to attain the nearest noble gas (stable) configuration .
30. Atomic number of an element is 12 . What is its valency ?
Ans : Its valency is equal to 2 because its electronic configuration is 2 , 8 , 2 . It can lose 2 electrons to become stable like noble gases .