science: chem

SCIENCE: 


TERMS:

Atom - smallest particle of an element that has the chemical properties of the element

Nucleus - found in the center of the atom

Proton - positively charged particle (in the nucleus)

Neutron - uncharged particle (in the nucleus)

Electron - negatively charged particle (moves our side the nucleus)


ATOMIC THEORY TIMELINE:

  • DEMOCRITUS and ATOMOS - 400 BC

    • Greek philosopher

    • Proposed that matter could not be divided into smaller pieces forever 

    • ATOMOS - small, hard particles that make up matter

  • ARISTOTLE 300 BC

    • Proposed that atoms were made up of FOUR ELEMENTS: air, fire, earth, water

  • JOHN DALTON and his ATOMIC THEORY - 1803 

    • Created the very first atomic theory

    • English school teacher

    • Viewed atoms as tiny, solid balls

    • FOUR STATEMENTS: (1) atoms are tiny, indivisible particles. (2) atoms of one element are all the same. (3) atoms of different elements are different . (4) compounds form by combining atoms.

    • Frederick Soddy and Isotopes

      • ISOTOPES - atoms of the same element with different masses (due to different numbers of neutrons)

  • JJ THOMPSON and his ELECTRON & RAISIN BUN MODEL

    • Joseph John Thompson discovered elections

    • First scientist to show that atoms were made of even smaller things 

    • Proposed the existence of a (+) particle






  • Created the RAISIN BUN MODEL:

  • ERNEST RUTHERFORD and NUCLEUS & PROTON - 1911

    • Discovered protons and nucleus

    • Showed that atoms have positively charged particles in the center

    • He called the (+) particles - PROTONS

    • He called the center of the atom - NUCLEUS

    • Conducted the gold foil experiment:

    • Most alpha particles (2 protons and 2 neutrons compacted) went through the gold foil. The atom had a dense center (nucleus)

  • NEILS BOHR and QUANTUM THEORY - 1913

    • Improved Rutherford’s model 

    • Proposed that electrons move around the nucleus in specific layers or shells

    • Every atom has a specific number of electron shells








  • ERWIN SCHRODINGER and the ELECTRON CLOUD MODEL - 1926

  • JAMES CHADWICK and THE NEUTRON - 1932 

    • Discovered the neutron

    • Working with rutherford, he discovered particles with NO CHARGE

    • Neutrons are also found in the nucleus

  • THE MODERN MODEL - 1932 to PRESENT

    • The new atomic model has electrons moving around the nucleus in the cloud 

    • It is impossible to know where an electron is at any given time 



STRUCTURE OF THE ATOM (ATOMIC NUMBER)

  • ATOMIC NUMBER - number of PROTONS in the nucleus

  • In a neutral atom (no charge)

    • No. of protons = no. of electrons

    • Atomic no. = no. of protons = no. of electrons

  • ATOMIC MASS NUMBER - sum of the numbers of protons and neutrons present in the nucleus of an atom (protons + neutrons)

    • Atomic mass no. = no. of protons + no. of neutrons

    • No. of neutrons = atomic mass no. - no. of protons

  • EXAMPLE

    • Element = Cl

      • Atomic mass no. = 35

      • Atomic number = 17

        • Protons = 17

        • Electrons = 17

        • Neutrons = 35 - 17 = 18