Question

Calculate the mass of an $\alpha$-particle in atomic mass unit (u).
Given: Mass of a normal helium atom = \( 4.002603 \ \text{u} \)
Mass of carbon atom = \( 1.9926 \times 10^{-26} \ \text{kg} \)

Hint:

An $\alpha$-particle is just the nucleus of a helium atom. To calculate its mass in atomic mass units (u), subtract the mass of two electrons from the helium atom’s atomic mass.

Answer 1

- An $\alpha$-particle is a helium nucleus, i.e., it consists of 2 protons and 2 neutrons (no electrons).
- A normal helium atom has 2 electrons. So, mass of $\alpha$-particle = mass of helium atom – mass of 2 electrons.
\[ \text{Mass of 1 electron} = 0.000548 \ \text{u} \Rightarrow \text{Mass of 2 electrons} = 2 \times 0.000548 = 0.001096 \ \text{u} \] Now, subtract: \[ \text{Mass of } \alpha\text{-particle} = 4.002603 - 0.001096 = 4.00150662 \ \text{u} \] Final Answer: 4.00150662 u