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Gen Chem 1 ch 7

Quantum-mechanical model of the Atom

quantum-mechanical model explains the manner in which electrons exist and behave in atoms
it helps us to predict: 1. why some elements are metals and others are nonmetals. 2.why some elements gain one electron when forming an anion, whereas others gain two. 3.why some elements are very reactive while others are practically inert and other periodic patterns we see in the properties of the elements
what does quantum mechanics have similar to light? wave-particle duality of light. (think of light as a wave.)
electromagnetic radiation 1.composed of perpendicular oscillating waves, one for the electric field and one for the magnetic field. 2.All electromagnetic waves move through space at the same, constant speed 3.00 x 10^8 m/s in a vacuum = the speed of light, c
electric field an electric field is a region where an electrically charged particle experiences a force
megnetic field a magnetic field is a region where a magnetized particle experiences a force
The Relationship Between Wavelength and Frequency 1. For waves traveling at the same speed, the shorter the wavelength, the more frequently they pass This means that the wavelength and frequency of electromagnetic waves are inversely proportional
The Electromagnetic Spectrum 1. Visible light comprises only a small fraction of all the wavelengths of light – called the electromagnetic spectrum 2.
interference waves, including electromegnetic waves, interact with each other in a characteristic way called INTERFERENCE: they cancel each other out or build each other up, depending on their alignment upon interaction.
constructive interference That if the two waves of equal amplitude are in phase when they interact- that is they align with overlaping crests- a wave with twice the amplitude results.
Destructive interference When waves interact so they cancel each other it is called destructive interference. -waves are out-of-phase
diffraction waves also exhibit a characteristic behavior called diffraction. When a wave encounters an obstacle or a slit that is comparable in size to its wavelength, it bends (or diffracts) around it.
Interference pattern The diffraction of light through two slits separated by a distance comparable to the wavelength of the light, coupled with interference, results in an INTERFERENCE PATTERN.
Interference pattern The diffraction of light through two slits separated by a distance comparable to the wavelength of the light, coupled with interference, results in an INTERFERENCE PATTERN.
Inerference is destructive and it creates a... ...dark line appears on the screen.
defraction model: we can see how waves bend, or diffract, when they encounter an obstacle or slit with a size comparable to their wavelength. When a wave passes through a small opening, it spreads out. Particles, in contrast, do not diffract; they simply pass through the opening.
The Photoelectric Effect 1. It was observed that many metals emit electrons when a light shines on their surface this is called the photoelectric effect 2.Classic wave theory attributed this effect to the light energy being transferred to the electron According to this theory, if the wavelength of light is made shorter, or the light waves’ intensity made brighter, more electrons should be ejected
Photoelectric Effect remember: remember: the energy of a wave is directly proportional to its amplitude and its frequency this idea predicts if a dim light were used there would be a lag time before electrons were emitted to give the electrons time to absorb enough energy
using light of a particular wavelength you can do what? 1. You can kick off an electron from the surface of the metal. 2. If you don't have enough electrons, the electron will not be kicked off.
threshold frequency 1. In experiments it was observed that there was a minimum frequency needed before electrons would be emitted 2. regardless of the intensity 3. It was also observed that high-frequency light from a dim source caused electron emission without any lag time
Einstein’s Explanation Einstein proposed that the light energy was delivered to the atoms in packets, called quanta or photons
Planck’s Constant, (h) and has the value 6.626 x 10−34 J∙s
Einstien suggested that light was... (hv) ... lumpy. A beam of light is NOT a wave propagating through space, but A SHOWER OF PARTICLES (PHOTONS), EACH WITH ENERGY hv.
the emission of an electron from a metal depends on: whether or not a single photon has sufficient energy(as given by hv) to dislodge a single electron.
binding energy (circle with line down middle). One photon at the threshold frequency gives the electron just enough energy for it to escape the atom
kinetic energy: When irradiated with a shorter wavelength photon, the electron absorbs more energy than is necessary to escape This excess energy becomes kinetic energy of the ejected electron
Spectra When atoms or molecules absorb energy, that energy is often released as light energy fireworks, neon lights, etc.
emission spectrum 1. When that emitted light is passed through a prism, a pattern of particular wavelengths of light is seen that is unique to that type of atom or molecule – the pattern is called EMISSION SPECTRUM 2. non-continuing can be used to identify the material flame tests
emission spectrum the result is a series of bright lines called an emission spectrum. Theemission spectrum of a particular element is always the same and can be used to identify the element.
Neils Bohr's model for the atom that explained atomic spectra. 1. In his model, electrons travel around the nucleus in circular orbits. 2. The electrons could only exist at a specific, fixed distances from the nucleus. 4. The energy of each Bohr orbit was also fixed or QUANTZED. 5. He called these orbits STATIONARY STATES. 6. They have an UNEXPLAINABLE STABILITY. 7. It was only when an electron jumped, or made a TRANSITION, from one stationary state to another that RADIATION was EMIITED or ABSORBED.
fixed or quantized quantized means that the atom could only have very specific amounts of energy
the electron is NEVER observed BETWEEN STATES: only in one state or the next- the transition between states is instanteous.
Rydberg’s Spectrum Analysis Rydberg analyzed the spectrum of hydrogen and found that it could be described with an equation that involved an inverse square of integers
Problems with Rutherford’s Nuclear Model of the Atom 1. Electrons are moving charged particles According to classical physics, moving charged particles give off energy 2. The electrons should lose energy, crash into the nucleus, and the atom should collapse!! but it doesn’t!
stationary states 1. The electrons travel in orbits that are at a fixed distance from the nucleus 2. therefore the energy of the electron was proportional to the distance the orbit was from the nucleus.
Electrons emit radiation when they “jump” from an orbit with higher energy down to an orbit with lower energy the emitted radiation was a photon of light the distance between the orbits determined the energy of the photon of light produced
Bohr's model was replaced by: the wave nature of the electron by Louis de Broglie. electrons are particles, but they also have A WAVE NATURE.
Wave Nature of an electron is seen most clearly in its diffraction.
Electron Deffraction Proof that the electron had wave nature came a few years later with the demonstration that a beam of electrons would produce an interference pattern as waves do
Electron Diffraction When a beam of electrons goes through two closely space slits, an interference pattern is created, as if the electrons were waves. In contrast, a beam of particles passing through two slits produces two smaller beams of particles. For particle beams, there is a dark line directly behind the center of the two slits, in contrast to wave behavior, which produces a bright line.
wave behavior or electrons (de Broglie) 1. de Broglie proposed that particles could have wave-like character 2. de Broglie predicted that the wavelength of a particle was inversely proportional to its momentum 3. Because it is so small, the wave character of electrons is significant
electrons are both: particles and have a wavelength
Complementary Properties 1. The wave and particle nature of the electron are complementary properties 2. When you try to observe the wave nature of the electron, you cannot observe its particle nature – and vice-versa 3. wave nature = interference pattern particle nature = position, which slit it is passing through.
the POSITION of an electron is related to... ... it's particle nature.
Quantum mechanical model also helps us to understand: 1. (any periodic patterns)It helps us understand and predict the properties of atoms that are directly related to the behavior of the electrons. More no bout one, less no bout other.The energy of a photon of light is directly proportional to its FREQUENCY 3. inversely proportional to its wavelength the proportionality constant is called Planck’s Constant, (h) and has the value 6.626 x 10−34 J∙s