Atomic Number and Synthesis of New Elements

ATOM MODELS

  • Dalton’s Billiard Ball Model
  • Thomson’s Plum Pudding Model
  • Rutherford’s Planetary Model
  • Bohr’s Model of the Hydrogen Atom
  • Schrödinger’s Electron Cloud Model

ARRANGEMENT OF THE ELEMENTS

  • Dobereiner: Triads
  • Newlands: Octaves
  • Mendeleev: arranged by increasing atomic weights; Father of the periodic table
  • Moseley: arranged by atomic number

ATOMIC NUMBER (Z)

  • The atomic number is the number of protons; ZZ from the German word Zahl (meaning number); identifies the element
  • The atomic number uniquely identifies a chemical element; ZZ determines most properties of the element

NUCLEAR TRANSMUTATION

  • Nuclear transmutation is the transformation of one element or isotope into another; involves protons and neutrons
  • Knowledge of the atomic number enables nuclear reactions

FIRST NUCLEAR TRANSMUTATION

  • Rutherford performed the first nuclear transmutation using an alpha particle

PARTICLE ACCELERATORS

  • To overcome repulsion between the nucleus and alpha particles, particle accelerators were used
  • Alpha particles are accelerated to very high speeds to overcome repulsive forces
  • A cyclotron is a particle accelerator that uses an alternating electric field to accelerate particles that move in a spiral path in the presence of a magnetic field

ELEMENT SYNTHESIS BY ACCELERATORS

  • Lawrence synthesized Technetium
  • Segre, Mackenzie and Corson synthesized Astatine

TRANSURANIUM ELEMENTS

  • Uranium is the heaviest known element by 1930; Z=92Z = 92
  • Elements with Z > 92 are known as transuranium elements
  • Transuranium elements are synthesized using particle accelerators

KEY DEFINITIONS AND FACTS

  • Atomic number: ZZ is the number of protons; identifies the element
  • Moseley’s contribution: the periodic table should be arranged by ZZ (atomic number)
  • Particle accelerator: device used to speed up particles to overcome repulsion between the particles and target nuclei
  • Cyclotron: a particle accelerator that uses alternating electric field to accelerate particles that move in a spiral path in the presence of a magnetic field