Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and iv) Isobars. Give any two uses of isotopes.
NCERT Class IX
Sciences - Exemplar Problems
Chapter 4. Structure of the Atom
Answers
◆ ATOMIC NUMBER
● the total no. of protons lying in the nucleus of any atom is called ATOMIC NUMBER
● An atomic no. is identify of an atom, changing atomic no. means changing the atom.
● It is denoted by 'Z'
● Atomic no. = no. of protons or no. of neutral atom, no. of protons and electrons are equal.
● Example -
1. Hydrogen
ATOMIC NUMBER = 1 (1 protons)
2. Helium
ATOMIC NUMBER = 2 (2 protons)
◆ MASS NUMBER
● It's defined as the sum of the number of protons and electrons present in the nucleus of an atom.
● It is denoted by 'Z'
● Mass no. = no. of protons + no. of electrons
Example -
1. Carbon
Mass no. = 12
6 protons + 6 electrons = 12
so, mass = 12u
2. Aluminum
Mass no. = 27
13 protons + 14 electrons = 27
so, mass = 27u
◆ ISOTOPES
● Isotopes are the atoms of same elements having same atomic no. and different mass no.
● Example - Chlorine has two isotopes of mass no. 35 and 37
17Cl35 , 17Cl37
● Uses
# Uranium isotopes is used as fuel in nuclear rector.
# Isotopes of cobalt is useful in treatment of Cancer.
# An isotopes of iodine is used in treatment of goiter.
◆ Isobars
● Isobars are the atoms of those elements which have the same mass no. but different atomic no. is called Isobars.
● 20Ca40 and 18Ar40 have same mass no. and different atomic no.
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ANSWER:-
◆ ATOMIC NUMBER
● the total no. of protons lying in the nucleus of any atom is called ATOMIC NUMBER
● An atomic no. is identify of an atom, changing atomic no. means changing the atom.
● It is denoted by 'Z'
● Atomic no. = no. of protons or no. of neutral atom, no. of protons and electrons are equal.
● Example -
1. Hydrogen
ATOMIC NUMBER = 1 (1 protons)
2. Helium
ATOMIC NUMBER = 2 (2 protons)
◆ MASS NUMBER
● It's defined as the sum of the number of protons and electrons present in the nucleus of an atom.
● It is denoted by 'Z'
● Mass no. = no. of protons + no. of electrons
Example -
1. Carbon
Mass no. = 12
6 protons + 6 electrons = 12
so, mass = 12u
2. Aluminum
Mass no. = 27
13 protons + 14 electrons = 27
so, mass = 27u
◆ ISOTOPES
● Isotopes are the atoms of same elements having same atomic no. and different mass no.
● Example - Chlorine has two isotopes of mass no. 35 and 37
17Cl35 , 17Cl37
● Uses
# Uranium isotopes is used as fuel in nuclear rector.
# Isotopes of cobalt is useful in treatment of Cancer.
# An isotopes of iodine is used in treatment of goiter.
◆ Isobars
● Isobars are the atoms of those elements which have the same mass no. but different atomic no. is called Isobars.
● 20Ca40 and 18Ar40 have same mass no. and different atomic no.