Atomic structure

• Atom


  Indivisible (in Greek)
• Living organisms and every non-living thing is composed of atoms
• Greek philosophers


  • Democritus
  • John Dalton
• Democritus


  • Explained the nature of matter
  • Proposed that all substances are made up of matter
  • Stated that atoms are constantly moving, invisible, minuscule particles that are different in shape, size, temperature and cannot be destroyed
• John Dalton


  • Proposed the first scientific theory of atomic structure
  • Atom was indivisible
  • All elements are composed of atoms
  • The same atoms for one element are exactly alike
  • Atoms are neither created nor destroyed in a chemical reaction
  • In a chemical reaction, atoms are separated, combined, or rearranged
• Democritus and Dalton were the first to put forward the concept of the atom
• J.J. Thomson


  • Used a cathode ray tube to detect negatively charged particles (electrons)
  • Calculated the charge to mass ratio of an electron

  
• Electron


  Negatively charged particle detected in cathode ray experiment
• The discovery of the electron was the first indication that atoms had internal structure
• Charge to mass ratio of electron

  • 1.76 x 10^8 C/g

  
• Charge of electron


  • 1.602 x 10^-19 C
• Mass of electron


  9.10 x 10^-28 g

  
• Thomson's plum-pudding model


  • Atom is a uniform, positive sphere of matter with electrons embedded and scattered like raisins in a cake

  
• Rutherford's atomic model


  • Atom has a dense, positively charged nucleus with electrons orbiting it

  
• Proton


  Positively charged particle in the nucleus

  
• Neutron


  Uncharged particle in the nucleus, equal in mass to proton

  
• The number of protons in the nucleus determines the atomic number of an element

  
• The number of electrons in an atom equals the number of protons, making the atom electrically neutral

  
• Importance of electrons


  • Stabilize the nuclear charge
  • Absorption and release of energy
  • Bonding (chemical bonding)
  • Determine chemical properties of elements
• Bohr's model of the atom

  • Electrons move in definite orbits or energy levels around the nucleus
  • Each orbit can hold a certain maximum number of electrons
  • Electrons can jump from orbit to orbit, releasing energy as light when jumping to lower orbits
  • Farther electrons are from nucleus, higher their energy
• Bohr's model was an important advance in atomic theory, but has some inaccuracies and limitations
• Planck's constant


  Proportionality constant relating energy and frequency of electromagnetic radiation (h = 6.626 x 10^-34 Js)
• Wave-particle duality


  Light and matter can exhibit both wave-like and particle-like behavior
• De Broglie relationship


  Particles have an associated wave with wavelength λ = h/mv
• Heisenberg Uncertainty Principle


  It is impossible to simultaneously determine the position and velocity of a particle
• The quantization of energy, wave-particle duality, and Uncertainty Principle led to the development of Wave Mechanics