CBSE-IX-Science
11: 2-Structure of the Atom
- Qstn #12If Z = 3, what would be the valency of the element? Also, name the element.Ans : When Z = 3, so that element has 3 electrons in its shells distributed as = 2, 1. Its valency is 1 because it can easily give away its outermost single electron and the element is Lithium(Li).
- Qstn #13Composition of the nuclei of two atomic species X and Y are given as under
Give the mass numbers of X and Y. What is the relation between the two species?
Ans : The mass number of X = 6+6 = 12
The mass number of Y = 6+8 = 14
since their number of protons are same but atomic mass are different so they are isotopes.
- #14-aJ.J. Thomson proposed that the nucleus of an atom contains only nucleons.Ans : false
- #14-bA neutron is formed by an electron and a proton combining together. Therefore, it is neutral.Ans : true
- #14-cThe mass of an electron is about 12000 times that of proton.Ans : true
- #14-dAn isotope of iodine is used for making tincture iodine, which is used as a medicine.Ans : false
Put tick (ü) against correct choice and cross (×) against wrong choice in questions 15, 16 and 17
- Qstn #15Rutherford’s alpha-particle scattering experiment was responsible for the discovery of
-(a) Atomic Nucleus
(b) Electron
(c) Proton
(d) Neutron
Ans : (c) proton
- Qstn #16Isotopes of an element have
-(a) the same physical properties
(b) different chemical properties
(c) different number of neutrons
(d) different atomic numbers.
Ans : (a) the same physical properties
- Qstn #18Which one of the following is a correct electronic configuration of sodium?
-(a) 2,8
(b) 8,2,1
(c) 2,1,8
(d) 2,8,1.
Ans : (a) 2,8,1
