Ch 4 chem

• Rutherford made predictions about the nucleus:

  • It is small
  • It is dense
  • It is positively charged
• Theories could not explain the structure of the atom outside of the nucleus
• Electrons are attracted to the nucleus
• To understand the motion of electrons, you need to know a little about the nature of light
• Electrons were viewed to be like particles

  • Light was viewed to be like a wave
  • To explain ALL observations, we describe both electrons and light as having a dual wave-particle nature
• 5 Behaviors of Waves that Light Exhibits:

  • Rectilinear Propagation: Waves travel in a straight path
  • Reflection: Bouncing back of waves that strike a surface
  • Refraction: Bending of waves as they pass from one medium to another
  • Diffraction: Spreading out of waves as they pass around a barrier or through an opening
  • Interference: The adding up or canceling out of waves traveling through the same medium
• Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space

  • It travels through a vacuum at a constant speed of 2.998x10^8 m/s
  • It has two measurable qualities: Wavelength (λ) and Frequency (υ)
• Wavelength (λ) is the distance between corresponding points on adjacent waves

  • Frequency (υ) is the number of waves that pass a given point in a specific amount of time
• Speed of light equation: c = λυ

  • As the frequency of light increases, its wavelength decreases
• The electromagnetic spectrum is a collection of electromagnetic waves covering a wide range of wavelengths and frequencies

  • Humans can see some but not all frequencies of electromagnetic radiation
• The photoelectric effect is the emission of electrons that occurs when light shines on a metal

  • Light must be a minimum frequency to knock electrons loose
• Max Planck proposed that a heated object emits energy as small, specific packets called quanta

  • A quantum of energy is the minimum quantity that can be lost or gained by an atom
• Planck's Quantum Theory:

  • Relationship between a quantum of energy and the frequency of radiation: E = hυ
  • Planck's Constant (h) is equal to 6.626x10^-34 J·s
• Einstein proposed that light is both a particle and a wave

  • Light particles are called photons
  • A photon is a particle of electromagnetic radiation having zero mass and carrying a quantum of energy
• Atoms absorb and emit energy:

  • Ground state is the lowest energy state of an atom
  • Excited state is when an atom has higher potential energy than in its ground state
  • When an atom goes back to its ground state, it gives off that energy as a photon of radiation
• Bohr proposed a model in 1913 to solve the puzzle of line emission spectra

  • Electrons are located in electron orbits or atomic energy levels
  • Only specific frequencies of energy can be absorbed and emitted by electrons
• Relationship between energy and electrons:

  • Absorption: Energy is taken in by an atom causing electrons to move to an excited state
  • Emission: Electrons fall back toward the ground state, releasing excess energy as a photon of light
• Photoelectric effect and hydrogen line emission showed that light could act as a wave and a particle

  • Louis deBroglie proposed that electrons were similar, confined to certain orbits and have certain frequencies
• Further experiments showed that electrons can be refracted, diffracted, and experience interference
• Electrons can be refracted, diffracted, and experience interference
• Heisenberg Uncertainty Principle states that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle
• Erwin Schrödinger hypothesized that electrons could be studied using mathematical equations for waves
• Schrödinger's wave equations proved Bohr's model of quantization of electron orbitals
• Electron orbitals contain only 2 electrons
• Electron configuration describes the locations of electrons in atoms, including energy level, sublevel, and number of electrons in that sublevel
• Orbitals are three-dimensional regions in space around the nucleus that indicate the probable location of an electron
• Aufbau Principal states that electrons will always be found as close to the nucleus as possible
• Hund's Rule states that if there are multiple orbitals in the same sublevel, each one must contain one electron before any can contain a second
• Pauli Exclusion Principal states that if there are two electrons in the same orbital, they will spin in opposite directions
• f orbitals are least stable with 1 or 8 electrons
• d orbitals are most stable with 5 or 10 electrons
• Noble Gas Configuration is a shorthand method representing only the outer electrons in an atom
• Valence electrons determine physical and chemical properties of an element
• Valence electrons are those electrons that are located in an atom's highest energy level
• Valence electrons can be predicted based on an element's location on the periodic table
• Dot Notation is used to show valence electrons, with each dot representing 1 valence electron