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, comprising 2 protons and 2 neutrons, with no electrons. - A standard helium atom possesses 2 electrons. Therefore, the mass of an $\alpha$-particle is equal to the mass of a helium atom minus the 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} ] Subtracting the mass of the electrons: [ \text{Mass of } \alpha\text{-particle} = 4.002603 - 0.001096 = 4.00150662 \ \text{u} ] Final Answer: 4.00150662 u