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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 framework describing matter as composed of discrete units, evolving from early philosophical ideas to modern models.
  • Democritus
    Ancient Greek thinker who first proposed the existence of indivisible particles as the fundamental building blocks of matter.
  • John Dalton
    Early 19th-century scientist who formulated foundational postulates about matter's composition, influencing modern chemistry.
  • Subatomic Particles
    Constituents of atoms, including protons, neutrons, and electrons, each with distinct properties and roles.
  • Proton
    Positively charged particle found in the nucleus, determining the atomic number and identity of an element.
  • Neutron
    Uncharged particle located in the atomic nucleus, contributing to atomic mass and isotope formation.
  • Electron
    Negatively charged particle orbiting the nucleus, involved in chemical bonding and electrical conductivity.
  • Isotope
    Variant of an element with the same number of protons but differing numbers of neutrons, resulting in different masses.
  • Mass Number
    Sum of protons and neutrons in an atom's nucleus, distinguishing isotopes of the same element.
  • Element
    Pure substance consisting of atoms with the same number of protons, represented on the periodic table.
  • Compound
    Substance formed from two or more different atoms chemically combined in specific ratios.
  • Chemical Reaction
    Process involving the rearrangement of atoms, resulting in the transformation of substances without creating or destroying matter.
  • Conservation of Mass
    Principle stating that matter is neither created nor destroyed during chemical processes, only transformed.
  • Modern Atomic Theory
    Current scientific understanding of atomic structure, incorporating subatomic particles and isotopic variation.