# Two stable isotopes of lithium Li36Li and Li37Li have respective abundances of 7.5% and 92.5%. These isotopes have masses 6.01512 u and 7.01600 u, respectively. Find the atomic mass of lithium. - Physics

Numerical

Two stable isotopes of lithium ""_3^6"Li" and ""_3^7"Li" have respective abundances of 7.5% and 92.5%. These isotopes have masses 6.01512 u and 7.01600 u, respectively. Find the atomic mass of lithium.

#### Solution

Mass of lithium isotope ""_3^6 "Li", m1 = 6.01512 u

Mass of lithium isotope ""_3^7 "Li", m2 = 7.01600 u

Abundance of ""_3^6 "Li", η1 = 7.5%

Abundance of ""_3^7 "Li", η2 = 92.5%

The atomic mass of lithium atom is given as:

"m" = ("m"_1η_1 + "m"_2η_2)/(η_1 + η_2)

= (6.01512 xx 7.5 + 7.01600 xx 92.5)/(92.5 + 7.5)

= 6.940934 u

Concept: Atomic Masses and Composition of Nucleus
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#### APPEARS IN

NCERT Physics Part 1 and 2 Class 12
Chapter 13 Nuclei
Exercise | Q 13.1 (a) | Page 462
NCERT Class 12 Physics Textbook
Chapter 13 Nuclei
Exercise | Q 1.1 | Page 462

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