CHEM QUIZ 8
explain diffraction.
diffraction occurs when a wave encounters an obstacle or a slit that is comparable in size to its wavelength. the wave bends around the slit. the diffraction of light through two slits separated by a distance comparable to the wavelength of the light results in an interference pattern
how did the photoelectric effect lead einstein to propose that light is quantized?
einstein proposed that light energy must come in packets. the amount of energy in a light packet depends on its frequency (wavelength). the emission of electrons depends on whether a single photon has sufficient energy to dislodge a single electron
explain electron diffraction.
electron diffraction occurs when an electron beam is aimed at two closely spaced slits and a series of detectors is arranged to detect the electrons after they pass through the slits. an interference pattern similar to that observed for light is recorded behind the slits. it is evidence of the wave nature of electrons.
what determines the color of light? what is the difference between red light and blue light?
for visible light wavelength determines the color. red light has a wavelength of 750 nm the longest of visible light, and blue has a wavelength of 500 nm
define frequency of electromagnetic radiation. how is frequency related to wavelength?
frequency is the number of cycles that pass through a stationary point in a given period of time. frequency is inversely proportional to wavelength.
describe the bohr model for the atom. how did the bohr model account for the mission spectra of atoms?
in the bohr model, electrons travel around the nucleus in circular orbits. bohr's orbits could exist only at specific, fixed distances from the nucleus. energy of each orbit is fixed (quantized). bohr called the orbits, stationary states and proposed that in contradiction to classical electromagnetic theory, no radiation was emitted by an electron orbiting the nucleus in a stationary state. it was only when an electron jumped, or made a transition, that radiations were emitted or absorbed. the emission spectrum of an atom consisted of discrete lines because the stationary states existed only at specific energies. the energy of the photon created when an electron made a transition from one stationary state to another was simply the energy difference between the two states
why is the quantum-mechanical model of the atom important for understanding chemistry?
it explains how electrons exist in atoms and how those electrons determine the chemical and physical properties of elements
what are the possible values of the magnetic quantum number ml? what does it determine?
it ranges from -l to +l. it specifies the orientation of the orbital.
what are possible values of the angular momentum quantum number l? what does it determine?
l is an integer greater than or equal to 0. it determines the shape of the orbital and can take value up to n-1
what is light? how fast does it travel in a vacuum?
light is electromagnetic radiation, a type of energy in oscillating electric and magnetic fields. it travels at 3.0 X 10^8 m/s
what are the possible values of the principal quantum number n? what does the principal quantum number determine?
n is an integer of possible values greater than 0. it determines the overall size and energy of an orbital
explain the difference between a plot showing probability density for an orbital and one showing the radial distribution function.
probability density is the probability per unit volume of finding the electron at a point in space. the radial distribution function represents the total probability of find the electron within a thin spherical shell at a distance r from the nucleus. in contrast to the probability density, radial distribution function has a value of 0 at the nucleus, it increases to a maximum and then decreases again with increasing r
list the sub levels and determine max number of electrons that can fit on the sub level.
s can hold a max of 2 electrons p can hold a max of 6 electrons d can hold a max of 10 electrons f can hold a max of 14 electrons
what is the de broglie wavelength of an electron? what determines the value of the de broglie wavelength for an electron?
the de broglie wavelength is associated with an electron traveling through space. it is related to its kinetic energy. the wavelength associated with an electron, moving at a velocity is wavelength = h/mv
what is the schrodinger equation? what is a wave function? how is a wave function related to an orbital?
the equation is a derivation of energies and orbitals for electrons in atoms. the symbol is the wave function, a function that describes the wave-like nature of the electron. E is the energy of the electron. a plot of the wave function squared represents an orbital
an electron behaves in ways that are at least partially indeterminate. explain.
the indeterminate behavior of an electron means that under identical conditions, the electron does not have the same trajectory and does not "land" in the same spot each time.
newton's laws of motion are deterministic. explain.
deterministic means that the present determines the future. that means that under the identical condition, identical results will occur.
what are complementary properties? how does electron diffraction demonstrate the complementarity of the wave nature and particle nature of the electron?
complementary properties exclude one another. the more you know about one, the less you know about the other. which of the two complementary properties you observe depends on the experiment being performed. in electron diffraction, when you try to observe which hole the electron goes through (particle nature), you lose the interference pattern (wave nature). when you observe the interference pattern, you lose the hole that the electron goes through
why are atoms usually portrayed as spheres when more orbitals aren't spherically shaped?
atoms are usually drawn as spheres because most atoms contain many electrons occupying a number of different orbitals so the shape of an atom is obtained by superimposing all of its orbitals.
what is a photon? how is the energy of a photon related to its wavelength? its frequency?
a photon is a packet of light. the energy of a photon can be expressed in terms of wavelength as E = (hc)/ w or in terms of frequency as E = hv
what is a probability distribution map?
a probability distribution map is a statistical map that shows where an electron is likely to be found under a given set of conditions
what is a quantum-mechanical orbital?
a probability distribution map showing where the electron is likely to be found
what is a trajectory? what kind of information do you need to predict the trajectory of a particle?
a trajectory is a path that is determined by the particle's velocity (speed and direction of travel), its position, and the forces acting on it. both position and velocity are required to predict trajectory
what is an emission spectrum? how does an emission spectrum of a gas in a discharge tube differ from a white light spectrum?
an emission spectrum occurs when an atom absorbs energy and reemits that energy as light. the light emitted contains distinct wavelengths for each element. the emission spectrum for a particular element is always the same and is used to identify the element. a white light spectrum is continuous, meaning there are no sudden interruptions in the intensity of the light. emission spectra are not continuous, they consist of bright lines at specific wavelengths with complete darkness in between.
describe the photoelectric effect. how did experimental observations of this phenomenon differ from the predictions of classical electromagnetic theory?
the photoelectric effect was the observation that many metals emit electrons when light shines on them. classical electromagnetic theory attributed this effect to the transfer of energy from the light to an electron in the metal, dislodging the electron. with this, changing the wavelength or amplitude of the light should affect the emission of electrons so the rate at which electrons were emitted could be increased by using light of shorter wavelength or higher intensity. dim light there should be lag time for the transfer of energy to the electron. experiments showed that light used to dislodge had a threshold frequency below which no electrons were emitted from the metal, no matter how long the light shone on the metal.
what determines the color of a colored object? explain why grass appears green?
the presence of a variety of wavelengths in white light is responsible for the way we perceive colors in objects. when a substance absorbs some colors while reflecting others, it appears colored. grass is green since it reflects primarily the wavelength associated with green light and absorbs others
why does the uncertainty principle make it impossible to predict a trajectory for the electron?
the uncertainty principle says that you cannot know both the position and the velocity of the electron simultaneously, you cannot predict the trajectory.
explain heisenberg's uncertainty principle. what paradox is at least partially solved by the uncertainty principle?
the uncertainty principle states that the product of x and mv must be greater than or equal to a finite number. the more accurately you know the position of the electron (smaller x) the less accurately you can know velocity (bigger v) and vice versa. complementarity of the wave nature and particle nature of the electron results in the complementarity of velocity and position. heisenberg solved the contradiction of an object as both a particle and a wave by introducing complementarity -- an electron is observed either as a particle or a wave, but never both at once.
define the wavelength and amplitude of a wave. how are these related to the energy of a wave?
wavelength is the distance between crests and amplitude is the height of the crest. the more closely the waves, the more energy there is. the amplitude of the electric and magnetic field waves determines the intensity of the light. the higher the amplitude the more energy the wave has
explain the wave behavior known as interference. explain the difference between constructive and destructive interference.
waves interact and either cancel each other out or build each other up, depending upon their alignment upon interaction. constructive interference occurs when waves of equal amplitude from two sources align with each other and a wave twice the amplitude results. destructive interference occurs when waves are completely out of phase - they align so the crest hits the trough of another wave - so they cancel each other
for each solution to the schrodinger equation, what can be precisely specified: the electron's energy or position? explain
we describe the probability distribution maps for electron states. in these, the electron has a well-defined energy, but not a well-defined position. for each state we can specify the energy of the electron precisely but not its location at a given instant. the position is described in terms of an orbital.