3.2 Subatomic Particles

Subatomic particles are the fundamental particles that make up atoms. The three main subatomic particles are:

  • Proton
    Relative charge: +1
    Relative mass: Approximately 1 atomic mass unit (amu) or 1.6726 x 10-27 kg
  • Neutron
    Relative charge: 0 (neutral)
    Relative mass: Approximately 1 atomic mass unit (amu) or 1.6749 x 10-27 kg
  • Electron
    Relative charge: -1
    Relative mass: Approximately 1/1836 amu or 9.11 x 10-31 kg

Protons and neutrons are found in the nucleus of an atom, whereas electrons orbit around the nucleus in energy levels or shells. They play crucial roles in determining the properties and behavior of atoms and molecules. Neutrons and protons are held together in the nucleus by a strong nuclear force. This force exists between neutron-neutron, proton-proton, and neutron-proton.

Relationships Between Subatomic Particles

Protons and neutrons have roughly the same mass, around 1 amu. This mass contributes significantly to the total mass of the atom. Electrons have much less mass, so their contribution to the total mass of an atom is usually negligible.

The interaction between the negatively charged electrons and positively charged protons in the nucleus is what holds the atoms together.

The Behavior of Subatomic Particles in an Electric Field

What happens when a beam of these particles passes between two electrically charged plates?

  • Protons are positively charged and are deflected on a curved path toward the negative plate.
  • Electrons are negatively charged and are deflected on a curved path toward the positive plate.
  • Neutrons have no charge, go straight ahead.

If the electrons and protons are traveling at the same speed, the electrons being lighter are deflected far more strongly than the heavier protons.

Path of positively and negatively charged particles through the uniform electric field
Figure 3.3: Path of positively and negatively charged particles through the uniform electric field.

Charge Neutrality

Atoms are electrically neutral because the number of protons (positively charged) in the nucleus is equal to the number of electrons (negatively charged) in the electron cloud. The charges balance each other so there is no net charge on the atoms.

Radioisotopes

Different isotopes of the same element have the same number of protons in their atomic nuclei but differing numbers of neutrons. Some isotopes of an element are unstable and show radioactive decay. Radioactive isotopes of an element can be defined as atoms that contain an unstable combination of neutrons and protons, or excess energy in their nucleus. For example, hydrogen-3 (protium), carbon-14, uranium-238, etc.