Atomic theory has undergone significant changes from Democritus's indivisible atoms to the discovery of subatomic particles and quantum mechanics. The structure of an atom, with its nucleus of protons and neutrons and electron orbits, defines its chemical properties and placement in the periodic table. Isotopes and ions illustrate the diversity within elements, while electron configurations dictate chemical reactivity. Historical milestones from Dalton to Bohr have shaped our understanding of the atom.
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Democritus first proposed the idea of atoms as the smallest indivisible units of matter
While the idea of indivisibility has been disproven, the concept of matter being composed of discrete units has persisted
Through scientific inquiry, the understanding of atomic structure has expanded to include the identification of subatomic particles and their behavior
The nucleus is the center of an atom and contains positively charged protons and neutral neutrons
Protons
Protons have a positive charge and contribute to an atom's mass
Neutrons
Neutrons have no charge and contribute to an atom's mass
Electrons
Electrons have a negative charge and orbit the nucleus at various energy levels
The specific arrangement of protons, neutrons, and electrons determines an atom's chemical properties and its position in the periodic table
Isotopes are atoms of the same element with differing numbers of neutrons, leading to variations in atomic mass while retaining similar chemical properties
The average atomic mass of an element is a weighted average of the masses of its isotopes, based on their natural abundance
The arrangement of electrons in an atom, organized into shells, subshells, and orbitals, influences an element's chemical properties and how it bonds with other atoms
Dalton's theory reintroduced the concept of atoms as fundamental particles
Thomson's discovery of the electron led to the "plum pudding" model of the atom
Rutherford's experiment revealed the existence of the atom's nucleus
Bohr's model introduced quantized electron orbits, laying the groundwork for the modern quantum mechanical model of the atom
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Evolution of atomic theory post-Democritus
Atomic theory expanded to include subatomic particles and their behaviors, beyond indivisible atoms.
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Subatomic particles identified
Protons, neutrons, and electrons are the subatomic particles that constitute atoms.
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Current view on atom's divisibility
Atoms are divisible into subatomic particles, contrary to the ancient Greek concept of indivisibility.
