6A Atomic Theory - Dado Science

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

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