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Atomic Theory definitions

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  • Atom
    Smallest unit of matter retaining chemical properties, once thought indivisible but now known to contain subatomic particles.
  • Atomic Theory
    Scientific explanation describing the nature, behavior, and structure of matter at the atomic level.
  • Democritus
    Ancient Greek philosopher who first proposed the existence of indivisible particles making up matter.
  • John Dalton
    Early 19th-century scientist who formulated foundational principles about the composition and behavior of atoms.
  • Postulate
    Fundamental assumption or principle forming the basis of a scientific theory, such as those in Dalton’s model.
  • Subatomic Particle
    Component found within atoms, including protons, neutrons, and electrons, not known in Dalton’s era.
  • Proton
    Positively charged particle located in the nucleus, determining the atomic number of an element.
  • Neutron
    Electrically neutral particle in the atomic nucleus, contributing to atomic mass and isotope formation.
  • Electron
    Negatively charged particle orbiting the nucleus, responsible for chemical bonding and reactivity.
  • Isotope
    Variant of an element’s atom with the same number of protons but different numbers of neutrons.
  • Compound
    Substance formed from two or more different atoms chemically combined in specific ratios.
  • Chemical Reaction
    Process involving the rearrangement of atoms, resulting in new substances without creating or destroying matter.
  • Conservation of Mass
    Principle stating that matter cannot be created or destroyed, only transformed during chemical changes.
  • Element
    Pure substance consisting of only one type of atom, defined by its number of protons.
  • Mass Number
    Sum of protons and neutrons in an atom’s nucleus, distinguishing isotopes of the same element.