Nuclear equations: and a beta particle by the symbol:

The idea

A beta particle is a fast-moving electron emitted from a nucleus during beta decay. In nuclear equations, it is written with the symbol β or e, carrying a mass number of 0 and an atomic number of −1. The top number is 0 because an electron has negligible mass; the bottom number is −1 because it has a single negative charge. For example, carbon-14 decays to nitrogen-14 and a beta particle: ¹⁴₆C → ¹⁴₇N + ⁰₋₁e (or ⁰₋₁β). The nucleon numbers balance (14 = 14 + 0) and the proton numbers balance (6 = 7 + (−1)). Writing the beta particle correctly as ⁰₋₁e or ⁰₋₁β is essential when balancing nuclear equations, because its 0 and −1 values explain why the mass number stays the same while the atomic number increases by 1.

What earns the marks

• A beta particle is represented by the symbol β or e with a mass number of 0 written as a superscript and an atomic number of −1 written as a subscript, for example ⁰₋₁e or ⁰₋₁β.
• The mass number of 0 shows that the emitted electron has negligible mass compared with protons and neutrons, so the total nucleon number of the nucleus is unchanged by beta emission.
• The atomic number of −1 shows that the beta particle carries a single negative charge, which balances the increase of 1 in the nuclear charge when a neutron changes into a proton.
• In a balanced nuclear equation, the sum of the mass numbers on the left equals the sum on the right, and the sum of the atomic numbers on the left equals the sum on the right.
• For example, in ¹⁴₆C → ¹⁴₇N + ⁰₋₁e, the mass numbers give 14 = 14 + 0 and the atomic numbers give 6 = 7 + (−1).

Common mistakes and how to put them right

• Writing the beta particle as ⁰₊₁e or ⁰₁β.

  Put it right: Use ⁰₋₁e or ⁰₋₁β because a beta particle is an electron with charge −1.

• Omitting the beta particle from the products of a nuclear equation.

  Put it right: Include ⁰₋₁e so that both mass numbers and atomic numbers balance.

• Confusing beta emission with alpha emission and writing ⁴₂He instead.

  Put it right: Check whether the atomic number increases by 1 (beta) or decreases by 2 (alpha) and use the matching symbol.

Exam tips

• When balancing a nuclear equation, write the mass numbers as a top row and the atomic numbers as a bottom row, then check each row separately.
• Remember that beta decay leaves the mass number unchanged but increases the atomic number by 1, so the new element is one place to the right in the periodic table.
• Practise writing the beta symbol with a superscript 0 and a subscript −1 (⁰₋₁e or ⁰₋₁β), and make sure the minus sign is clearly attached to the 1.