Question 16: What happens to the atomic number and mass number of nucleus that (a) emits electron (b) undergoes electron capture (c) emits α particle?

ANSWER

Emission of electron

When a neutron converts to proton in a nuclear reaction, an electron is emitted.

₀n¹   —–>₁P¹ + e^’

With this emission, the charge number increases by one unit because a neutron is converted to proton but there is no change in the mass number of the nucleus.

The general equation of electron emission reactions is
_ZX^A —–> _Z+1Y^A + β^–

As an example,
₆C¹⁴ —–> ₇C¹⁴ + β^–

Capture of electron

Sometimes an electron from the inner shells of the atom is dragged by the nucleus where it combines with a proton. As a result the proton is converted to a neutron and a neutrino is emitted. With a proton converted to neutron, there is obviously a decrease in the charge number. However, there is no change in the mass number of the nucleus because there is no change in the number of nucleons in the nucleus. The reaction is

_ZX^A + β^– —–> _Z-AY^A + ν

Example
₄Be⁷ + β^– —–> ₃Li⁷ + ν

Emission of α particle

An α particle is a helium nucleus. Therefore, when a nucleus emits an α particle, its charge number decreases by two units and mass number by four units.

General equation of the reaction is
_ZX^A —–> _Z-2Y^A-4 + ₂He⁴
₉₀Th²²⁷ —–> ₈₈Ra²²³ + ₂He⁴