Question

Helium is the lightest noble gas and the second most abundant element (after hydrogen) in the universe. The mass of a helium−4 atom is 6.64648 × 10−24g, and each of its two electrons has a mass of 9.10939 × 10−28g. What fraction of this atom's mass is contributed by its nucleus?

Answer 1

Answer: The fraction of atom's mass contributed by nucleus is 0.99

Explanation:

Nucleons are defined as the sub-atomic particles which are present in the nucleus of an atom. Nucleons are protons and neutrons.

The isotopic symbol of Helium-4 atom is $_2^4\textrm{He}$

Number of electrons = 2

Number of protons = 2

Number of neutrons = 4 - 2 = 2

We are given:

Mass of He-4 atom = $6.64648\times 10^{-24}g$

Mass of 1 electron = $9.10939\times 10^{-28}g$

Calculating the mass contributed by the nucleus = $m_{He}-2(m_e)$

Mass of the nucleus of He-4 atom = $6.64648\times 10^{-24}-(2\times (9.10939\times 10^{-28}))=(6.64648-0.0018219)\times 10^{-24}=6.64466\times 10^{-24}$

To calculate the fraction of atom's mass contributed by the nucleus, we use the equation:

$\text{Fraction of atom's mass contributed by nucleus}=\frac{\text{Mass of nucleus}}{\text{Mass of atom}}$

Putting values in above equation, we get:

$\text{Fraction of atom's mass contributed by nucleus}=\frac{6.64466\times 10^{-24}g}{6.64648\times 10^{-24}g}=0.99$

Hence, the fraction of atom's mass contributed by nucleus is 0.99