Electron
Summary: An electron is a negatively charged subatomic particle with negligible mass (relative mass 1/1836) that occupies shells around the nucleus, governs chemical bonding, and is responsible for electrical conduction in metals. Tags: igcse chemistry Created: 2026-07-18
The Electron is a fundamental subatomic particle that carries a relative negative charge of -1 and has an extremely small mass — approximately 1/1836 of the mass of a Proton, which is effectively negligible when calculating relative atomic mass. Unlike protons and neutrons, which reside in the dense central nucleus, electrons exist outside the nucleus in specific regions called electron shells (also called energy levels), where they move rapidly and occupy most of the atom’s volume. The number of electrons in a neutral atom equals the number of protons (the atomic number), ensuring overall electrical neutrality. Electrons are the subatomic particles most directly involved in chemical bonding: they are transferred in ionic bonding, shared in covalent bonding, and delocalised in metallic bonding. Their arrangement, described by the Electronic Configuration, determines an Element’s chemical properties, reactivity, and position in the Periodic Table.
Properties of the Electron
Charge and Mass
The Electron has the following key properties:
| Property | Value |
|---|---|
| Relative charge | -1 |
| Actual charge | -1.602 x 10^-19 C |
| Relative mass | 1/1836 (approximately 0.0005) |
| Actual mass | 9.109 x 10^-31 kg |
| Location | Electron shells surrounding the nucleus |
| Symbol | e or e^- |
The Electron is approximately 1836 times lighter than a Proton or Neutron. Because of this negligible mass, electrons contribute virtually nothing to the total mass of an atom, which is essentially determined by the number of protons and neutrons in the nucleus. However, despite their tiny mass, electrons dominate the volume of the atom and are responsible for all ordinary chemical behaviour.
Arrangement in Shells
Electrons are arranged around the nucleus in specific electron shells (energy levels). For the first 20 elements of the Periodic Table, the filling rules are:
- 1st shell: holds a maximum of 2 electrons
- 2nd shell: holds a maximum of 8 electrons
- 3rd shell: holds a maximum of 8 electrons (for the first 20 elements)
The arrangement of electrons in these shells is called the Electronic Configuration. For example, sodium (Z = 11) has the electronic configuration 2.8.1, meaning 2 electrons in the first shell, 8 in the second, and 1 in the third (outer) shell. The number of electrons in the outermost shell determines the chemical properties and reactivity of the element. Electrons in the outermost shell are called valence electrons.
Role in Chemical Bonding
Electrons are central to all three types of chemical bonding:
- Ionic bonding: electrons are transferred from a metal atom to a non-metal atom. The metal loses electrons to become a positive Ion (cation), and the non-metal gains electrons to become a negative Ion (anion). The oppositely charged ions attract each other by electrostatic forces.
- Covalent bonding: electrons are shared between non-metal atoms. Each shared pair of electrons forms one covalent bond, enabling each atom to achieve a full outer shell (noble gas configuration).
- Metallic bonding: electrons in the outer shells of metal atoms become delocalised — free to move throughout the metal lattice. This sea of delocalised electrons holds the positive metal ions together.
In all cases, atoms bond in order to achieve a stable outer-shell electron arrangement, typically a full outer shell of 2 or 8 electrons (the noble gas configuration). This is sometimes called the octet rule.
Role in Electrical Conduction
Electrons are the charge carriers responsible for electrical conductivity:
- In metals and graphite, delocalised electrons can move freely through the structure, carrying electric current.
- In electrolysis, electrons are transferred between species at the electrodes, enabling the flow of current through the external circuit.
- Covalent compounds (simple molecular structures) do not conduct electricity because there are no mobile charged particles — all electrons are either held in covalent bonds or as lone pairs within the molecules, and the molecules themselves are neutral.
The gain or loss of electrons also defines oxidation and reduction: oxidation is the loss of electrons, and reduction is the gain of electrons (OIL RIG: Oxidation Is Loss, Reduction Is Gain).
Sources
- Cambridge IGCSE Chemistry 0620 Syllabus (2023-2025) — Section 2.2, Cambridge Assessment International Education
Common Misconceptions
| Misconception | Reality |
|---|---|
| ”Electrons orbit the nucleus in fixed circular paths like planets” | Electrons occupy shells (energy levels). The shell model describes energy levels and probabilities, not fixed orbits like planets around the Sun |
| ”Electrons are stationary within their shells” | Electrons are in constant rapid motion around the nucleus. The shells represent energy levels, not fixed positions |
| ”The electron mass contributes significantly to atomic mass” | The mass of an electron is approximately 1/1836 of a proton — negligible for atomic mass calculations. Atomic mass is essentially the sum of proton and neutron masses |
| ”Electrons and protons attract each other by gravity” | The attraction between electrons and the nucleus is electrostatic (electromagnetic), not gravitational. Gravity is negligible at the atomic scale |
| ”When atoms lose electrons, protons are also lost” | Only electrons are lost or gained in chemical reactions and ion formation. The number of protons in the nucleus never changes during chemical processes |