6a atomic theory - dado science
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Atomic Theory
Chemistry 6A
• Dalton’s Postulates – Elements are made of small and indivisible particles called atoms – Atoms of a given element are identical to one another but differ from
atoms of other elements – Chemical reactions occur when atoms are combined, separated, or
rearranged in simplified whole-number ratios – Atoms are neither created nor destroyed in chemical reactions
• Thomson’s discovery of electron properties – Cathode rays were attracted to a positively charged plate
• Cathode ray – stream of electrons • Electron – negatively charged subatomic particle • Disproved Dalton’s Postulate that atoms were indivisible
Cathode Ray Tube
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Atomic Theory
Chemistry 6A
• Rutherford’s nuclear atom – Most alpha particles passed through gold foil, while some deflected
back • Nucleus – positively charged, dense center of an atom
– Nucleus contains protons and neutrons
• Proton – positively charged subatomic particle • Neutron – neutrally charged subatomic particle
• Bohr’s nuclear atom – Proposed that electrons
• Are arranged in circular orbits around the nucleus
• Do not lose energy as they orbit • In each orbit have fixed amount of energy • In an orbit closest to the nucleus are in their
lowest energy state • Gain and lose energy in certain, fixed amounts
called quanta • May receive energy and move to a higher energy orbit • Return back to lower energy orbit when they release energy
– Photon – particle of electromagnetic radiation that possesses a quantum of energy
• Energy of each photon corresponds to a certain frequency