Class 9 Science Chapter 4 Case Based Questions - Structure of the Atom

(I) Read the given passage and answer the questions based on the passage and related studied concepts.
Atom consists of electrons, protons and neutrons. J.J. Thomson proposed that electrons are embedded in a positive charge uniform sphere. Rutherford a-scattering experiment led to discovery of nucleus in the centre of atom which is positively charged and whole mass of atom is concentrated in the nucleus. Neil Bohr proposed that electrons are distributed in different shells in M, N... with discrete energy around the nucleus. If atomic shell is complete, atom will be stable and less reactive. Electrons are negatively charged, protons are positively charged, neutrons are neutral. Valency is the combining capacity of an atom. Atomic number is equal to number of protons in an atom. The mass number of an atom is equal to sum of number of protons and neutrons in the nucleus. Isotopes have same atomic number but different mass numbers. Isobars have same mass number but different atomic numbers. Elements are defined by number of protons (atomic number) they possess.
Q1: Which of the following does not contain neutron? 
(a) Al
(b) Na
(c) H
(d) Mg
Ans: Hydrogen (H) does not contain neutron.

Q2: What is the atomic number of Al³⁺, if it has 13 protons, 10 electrons, 14 neutrons?
(a) 13
(b) 10
(c) 14
(d) 27
Ans: (a) 13, Atomic number is equal to number of protons.

Q3: Write electronic configuration of K.
Ans: 2, 8, 8, 1

Q4: Isotopes differ in which sub-atomic particles?
Ans: Neutrons

(II) Observe the Bar-chart shown for elements with atomic number 1 to 10. Answer the questions based on this graph and related studied concepts.
Q1: Name the element whose first shell is complete.
Ans: Helium

Q2: Name the element in which second shell has twice electrons than 1^st shell.
Ans: C(2, 4)

Q3: How does valence electrons vary from Li to Ne?
Ans: Valence electrons increase from Li to Ne.

Q4: Name the element which has 7 valence electrons.
Ans: Fluorine (F) 2, 7.