Final answer:
A beta particle is a high-energy electron emitted from the nucleus during beta decay, which increases the atomic number of the atom.
Step-by-step explanation:
A beta particle is best described as an electron that is emitted from the nucleus of an atom during a type of radioactive decay known as beta decay. This process occurs in nuclei where the neutron-to-proton ratio is too high for stability; thus, a neutron is transformed into a proton and a beta particle, which is then ejected at high speed. The beta particle can be represented by the Greek letter β or as an e- with an atomic number of -1 and a charge of -1. The mass of the beta particle is considered negligible in comparison to that of protons and neutrons.
When a beta particle is emitted, the atomic number of the nucleus increases by one since a neutron has been converted into a proton, but the overall mass number remains unchanged because the proton and neutron have nearly the same mass. An example of beta decay is the transformation of carbon-14 into nitrogen-14, in which a beta particle is released. Contrary to beta particles, positron emission occurs in nuclei where the neutron-to-proton ratio is too low; here, a proton transforms into a neutron and a positron (a positively charged electron) which is also ejected immediately.
In summary, a beta particle is a high-speed electron with a -1 charge that originates from within the nucleus during radioactive decay, leading to an increase in the atomic number of the atom, unlike alpha particles, which are helium nuclei, and gamma rays, which are high-energy electromagnetic radiation.