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What are isotopes?
Atoms of same element which have different mass number but same atomic number
Example - 1
- Hydrogen Element has 3 isotopes:-
- Protium
- Deuterium
- Tritium
Difference between Different Isotopes of Hydrogen
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Protium |
Deuterium |
Tritium |
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It has an atomic number = 1 and mass number = 1. |
It has atomic number = 1 and mass number = 2. |
It has atomic number = 1 and mass number = 3. |
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It has only 1 proton and 0 neutron |
It has only 1 proton and 1 neutron. |
It has only 1 proton and 2 neutrons. |
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Protium for hydrogen is denoted as |
Deuterium for hydrogen is denoted as |
Tritium for hydrogen is denoted as |
Example - 2
- Chlorine Element has 2 isotopes:-
- Chlorine - 35
- Chlorine - 37
Difference between Different Isotopes of Chlorine
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Chlorine-35 |
Chlorine-37 |
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It has an atomic number 17 and mass number 35. |
It has an atomic number 17 and mass number 37. |
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Nuclear composition of Cl-35 isotope is = 17 protons + 18 neutrons. |
Nuclear composition of Cl-37 isotope is = 17 protons + 20 neutrons. |
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Chlorine-35 is denoted as |
Chlorine-37 is denoted as |
How is Mass of Isotope Calculated?
- It is the average of mass of both isotopes.
- The mass of isotopes depends on how much of which isotope exists in nature .
Example
- Chlorine Element has 2 isotopes:-
Chlorine-35 → It has a mass of 35 u, 75% of chlorine exists in the form of this isotope of chlorine.
Chlorine-37 → It has a mass of 37 u, 25% of chlorine exists in the form of this isotope of chlorine
- The relative mass of chlorine atom can be calculated as follows:-
Average Mass of Chlorine = (35 + 37)/2
= 35.5 u
Mass of chlorine = [(75/100) x 37] + [(25/100) x 35]
= [(3 x 37)/4] + [(1x35)/4]
= 35.5 u
Hence, a general formula can be derived as follows: -
Average mass of an isotope = ( % existence of the isotope 1 x mass of isotope 1) +
( % existence of the isotope 2 x mass of isotope 2) +
( % existence of the isotope 3 x mass of isotope 3) and so on...
Properties of isotopes
- They have same number of Protons and hence same atomic number
- Chemical Properties of Different Isotopes are similar
- However Physical Properties of Different isotopes are different
Applications/Uses of isotopes
-
Isotope of Uranium (Uranium 235)
It is used as fuel in Nuclear Reactors
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Isotope of Cobalt (Cobalt-60)
It is used for treatment of cancer
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Isotope of Iodine (Iodine 131)
It is used for treatment of goitre
Examples -
In text Question - Page 53 Q1, Q2
NCERT Back Exercise - Q8(iii), Q10, Q11, Q13, Q14(iv), Q16
What are Isobars?
Atoms of Different elements have the same mass number , but different atomic numbers are called Isobars.
Example
- Calcium atoms have atomic number 20 and mass number 40.
- Argon has atomic number 18 and mass number 40.
- Since both have the same mass number.
- Calcium and Argon are Isobars.
Note - Argon has 18 protons + 22 neutrons = Atomic mass = 40
Calcium has 20 protons + 20 neutrons = Atomic mass = 40
Difference between Isotopes and Isobars
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Isotopes |
Isobars |
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Isotopes are atoms of the same element. |
Isobars are atoms of different elements. |
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They have the same atomic number but different mass number. |
They have different atomic numbers but same mass numbers. |
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Number of protons and electrons in isotopes are the same . |
Number of protons and electrons in isobars is different . |
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They have the same chemical properties. |
They have different chemical properties. |
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Example: Isotopes of Hydrogen - Protium, Deuterium, Tritium |
Example: Isobars - Carbon and Argon.
|
Examples -
In text Question -
NCERT Back Exercise - Q8(iv)
