PIC MODULE 2

atoms - smallest unit of matter; building blocks of matter.

atoms - they makes up the element

subatomic particles : PROTON, NEUTRON, ELECTRON

PROTON - positive charge (+)

NEUTRON - no charge

ELECTRON - negative charge (-)

PROTONS AND NEUTRONS - located at the NUCLEUS; have the same mass

ELECTRONS - located at the SHELL; have negligible mass

NEUTRAL ATOM - contains equal numbers of protons and electron; no charge

POSITIVELY CHARGED ATOM - nucleus of atom contains + and 0 only.

ATOMIC THEORIES/HISTORY OF ATOM:

  1. DEMOCRITUS - all matter consists of very small, invisible particles (atomos)

    ATOMOS - meaning uncuttable or indivisible

  2. JOHN DALTON (1803) - Billiard Ball Model / Solid Sphere Model

    -English Scientist and school teacher who formulated a precise definition of atom.

  3. JOSEPH JOHN THOMSON (J.J. THOMSON) - Raisin-Bread Model/ Plum Pudding Model

    -He discovered that atom is a sphere of positive particle to which are embedded the negative particles called electrons

    -He discovered electrons

  4. ERNEST RUTHERFORD - Nuclear Model; Gold Film Experiment

    -He discovered proton through GFE; atom is mostly an empty space (99% passed, <1% dejected)

    -He discovered nucleus

  5. NIELS BOHR - Planetary Model

    -Electronic structure: electrons moves around the nucleus in circular orbits.

  6. ERWIN SCHRODINGER - “Electron cloud”; Quantum Mechanical Model

    -electrons move in 3D structure which is called electron cloud. Electron is not a particulate but a quantity.

  7. JAMES CHADWICK - He bombarded a thin sheet of Beryllium with alpha particles, and very high energy similar to gamma rays was emitted by the metal.

    -He discovered neutron.