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CORC1322 MAIN PAGE

MATTER

Introduction
Atoms and Molecules

ATOMIC STRUCTURE

Introduction
Electrons
Protons
Neutrons

REACTIONS

Introduction
Bonds and Octet Rules
Chemical Equations
The Mole

SOLVING PROBLEMS

Density
Conversions

VISUAL AIDS

Functional Groups
Periodic Table

QUIZZES

Practice Quiz I
Practice Quiz II
Practice Quiz III

Electrons

The electron is one of the three principal sub-atomic particles in the atom. Electrons are charged particles, carrying a small negative charge. Electrons orbit the nucleus in specific energy levels/shells at super–high speeds. Electrons are incredibly small. It is almost as if they have no mass whatsoever compared to the rest of the atom.

An electron in an atom

This is an imaginary construct being used for illustrative purposes.

Every atom has a specific number of electrons that surround the nucleus, and if the atom is neutral (has no charge), that number is equal to the number of protons in the atom's nucleus. When atoms enter into chemical reactions, electrons can be lost, gained, or shared by the participating atoms. Since the number of electrons in an atom does not determine the atom's identity, these electron changes do not alter the identities of the atoms involved.

The discovery of the electron occurred in 1897 when English physicist Sir Joseph John Thomson showed that the beams that are produced by electricity in a cathode ray tube (a glass tube evacuated of air, with two metal pieces at the ends connected to a battery) deflected toward the positive end of an electric field. He thus concluded that cathode rays had to consist of negatively charged particles, which he called electrons. He found them to be present regardless of what material was placed inside the cathode ray tube. From this evidence, he concluded that all atoms possessed electrons.

Diagram of Thomson's Cathode Ray Tube