Module 1

• John Dalton -

  showed that ratios of masses of an element combining with a gram of another element can always be reduced to small whole numbers
• Dalton’s Atomic Theory

  1. Each element is made up of tiny particles called atoms.
  2. The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.
  3. Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative numbers and types of atoms.
  4. Chemical reactions involve reorganization of atoms - changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.
• Joseph John Thomson

  • studied electrical discharges in partially evacuated tubes (CRT)
  • discovered the electron (corpuscles)
  • e/m = –1.76 x 108 C/g
• joseph john thompson discovered the plum pudding
• Robert milikan

  • performed experiments using oil drops

  • me = 9.11 x 10–31 kg

  • calculated the of an electron
• rutherford

  performed an experiment to test Thomson’s atomic model

  • α particle bombardment of a metal foil
• James chadwick

  • performed an experiment that led to the discovery of neutrons

  • α particle bombardment of a beryllium sheet
• Dalton’s Solid Sphere Model

  recognized that atoms of a particular element differ from other elements
• Thomson’s Plum Pudding Model

  recognized electrons as components of atoms

  no nucleus (wrong)
• Rutherford’s Nuclear Model

  • realized that a positive charge was localized in the nucleus of the atom
• wave is a vibrating disturbance

  by which energy is transmitted.”
• “An electromagnetic radiation is

  an emission or transmission of

  energy in the form of electromagnetic waves.”
• speed of light (3.00 x 10^8 m/s)
• interference is the net effect of the combination of two or more waves moving on intersecting or coincident paths.
• Diffraction is a phenomenon resulting from interference where waves spread around an obstacle.
• Max Planck

  discovered that atoms and molecules emit energy only in certain discrete quantities

  (quanta)
• where h = Planck’s constant = 6.63 x 10–34 J∙s
• Albert Einstein (1879 - 1955)

  • explained the

  photoelectric effect

  • suggested that a beam of light is made of particles (representing a quantum of light) Called photons
• The photoelectric effect is a

  phenomenon in which electrons

  are ejected from the surface of certain metals exposed to light of at least a certain minimum frequency (threshold frequency).
• threshold frequency (ν0) is the minimum frequency required to remove an electron from the metal surface.
• The ability of the light to eject an electron depends only on frequency

  and not on the intensity.

  Only a photon of

  sufficient energy can

  eject an electron.
• Light is emitted as an electron moves from a high energy level to a low energy level.
• Niels Bohr

  • explained the emission spectrum of the hydrogen atom

  • postulated that an electron is allowed to occupy only orbits of specific energy
• Niels Bohr

  • The electron moves about the nucleus with speed u in one of a fixed set of circular orbits

  • The electron’s angular momentum is an integer multiple of h/2π

  • An atom emits energy as a photon when an electron falls from an orbit of higher energy and larger radius
• Bohr’s Planetary Model

  (Correct) proposed stable electron orbits; explained the emission spectra of some elements

  (Wrong) model did not work well for heavier atoms
• Louis de Broglie

  particles (like electrons) have wave properties
• Planck: Energy is quantized

  Einstein: Light is quantized

  • light has particle-like properties

  de Broglie: Electron energy is

  quantized

  • electrons display wave-like properties
• Werner Heisenberg (1901 - 1976)

  • “It is impossible to know simultaneously both the momentum and the position of a particle with certainty.”

  • atoms and electrons exhibit wavelengths that can be measured
• Heisenberg’s Uncertainty

  • large momentum = short wavelength

  • atoms and electrons exhibit wavelengths that can be measured

  • when we overlap waves, regions that coincide with each other increases in amplitude, and those that do not cancel

  • adding more waves with varying wavelengths will cause the waves to be

  localized forming a wave pocket

  • the more waves combined, the more precisely the particle is located but momentum becomes more uncertain
• According to the Heisenberg’s Uncertainty,

  • to determine the position with certainty, you need more waves

  • to determine the momentum, you need a larger wave packet
• Erwin Schrödinger (1887 - 1961)

  • formulated wave mechanics which laid the foundation for modern quantum theory

  • suggested that an electron exhibiting wave properties should be described by a mathematical equation called a

  wave function, Ψ
• Max Born (1882 - 1970)

  • The total probability of finding a particle in a small volume of space is the product of the square of the wave function, Ψ2

  (probability density)
• Particle in a 3D Box

  • for a three-dimensional system, the particle can move in three directions

  • each dimension must have one quantum number

  • a three-dimensional system will need three quantum numbers
• Quantum Mechanical Model

  • introduces the concept of an electron density which gives the probability that an electron will be found in a particular region of an atom
• Quantum numbers are mathematical solutions of the

  Schrödinger equation for a hydrogen atom that describe the

  orbital (wave properties of an function).”
• orbital

  • square of the wave function indicates the probability of finding an electron near a particular point in space (The probability distribution).
• Nodes are regions of no electron density.
• Principal quantum number, n

  • has positive non-zero integral values 1, 2, 3...

  • related to the size and energy of the orbital

  • related to the average distance of the electron from the nucleus

  • principal electronic shell – orbitals with the same value of n
• Angular momentum quantum

  number, l

  • has integral values from 0 to n – 1 for every value of n

  • related to the shape of the orbital

  • subshell – orbitals with a given angular momentum quantum number

  • the number of subshells in a principal shell is equal to n
• Magnetic quantum number, ml

  • has integral values from – l to + l including zero

  • related to the orientation of an orbital in space relative to the other orbitals