History of Atomic Theory

Atomic Theory History

• Atoms are the smallest particles of an element.
• Atoms are the smallest amount of a substance that participates in chemical reactions.
• Democritus, a Greek philosopher, searched for a description of matter.
• He named the smallest piece of matter "atomos" (indivisible).
• These atoms were small, hard particles, all made of the same material, but different shapes and sizes.
• John Dalton (English chemist) performed experiments leading to the acceptance of the atomic theory.
• He deduced that all elements are composed of atoms.
• Atoms of the same element are exactly alike.
• Atoms of different elements are different.
• Compounds are formed when atoms of different elements combine.
• J.J. Thomson (English scientist) discovered the electron and suggested the "Plum Pudding" model.
• Atoms have structure—a positively charged substance, with negatively charged electrons embedded in it, like plums in a pudding.
• Ernest Rutherford (English physicist) conducted experiments to understand the atom's structure.
• He found that atoms contain a small, dense, positively charged nucleus.
• Negatively charged electrons orbit around this nucleus.
• Niels Bohr (Danish scientist) refined Rutherford's model.
• Electrons orbit the nucleus in specific energy levels.
• Arnold Sommerfeld refined Bohr's model to include elliptical orbits for electrons.
• Erwin Schrödinger (physicist and biologist) considered the Father of Quantum Mechanics; today's atomic model is based on the principles of wave mechanics.
• Electrons do not move in fixed paths like planets around the sun; instead, space in which electrons are likely to be found is termed electron cloud.
• The arrangement of electrons in energy levels around the atom's nucleus is called electron configuration. The energy levels are further divided into sublevels (s, p, d, and f). Each sublevel contains specific number of orbitals.