Atomic Structure

Samacheer Book Back Questions And Answers For Science Standard 9 “Atomic Structure“

I. Choose the correct answer:
1. Among the following the odd pair is
(a) 188O, 199F
(b) 4018Ar, 147N
(c) 3014Si, 3115P
(d) 4020Cr, 3919K

2. Change in the number of neutrons in an atom changes it to
(a) an ion.
(b) an isotope.
(c) an isobar.
(d) another element.

3. The term nucleons refer to
(a) protons and electrons
(b) only neutrons
(c) electrons and neutrons
(d) protons and neutrons

4. The number of protons, neutrons and electrons present respectively in 8035Br are
(a) 80, 80, 35
(b) 35, 55, 80
(c). 35, 35, 80
(d) 35, 45, 35

5. The correct electronic configuration of potassium is
(a) 2,8,9
(b) 2,8,1
(c) 2, 8, 8, 1
(d) 2, 8, 8, 3

II. State true or false. If false, correct the statement:
1. In an atom, electrons revolve around the nucleus in fixed orbits.
2. Isotopes of an element have different atomic numbers.
3. Electrons have negligible mass and charge.
4. Smaller the size of the orbit, lower is the energy of the orbit.
5. The maximum number of electron in L Shell is 10.

Answers:
1. True
2. False (Same atomic numbers but different mass numbers)
3. True
4. True
5. False (The maximum number of electrons in L Shell is 8)

III. Fill in the blanks:
1. Calcium and Argon are examples of a pair of _____.
2. Total number of electrons that can be accommodated in an orbit is given by _____.
3. _____ isotope is used in the nuclear reactors.
4. The number of neutrons present in 37Li is _____.
5. The valency of Argon is _____.

Answers:
1. isobars
2. 2n²
3. Uranium-235
4. 4
5. Zero

IV. Match the following:
1. Dalton              A. Hydrogen atom model
2. Chadwick         B. Discovery of nucleus
3. Rutherford      C. First atomic theory
4. Neils Bohr       D. Plum pudding model
E. Discovery of neutrons

Answers:
1. C
2. E
3. B
4. A

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