# [CHM135H1] - Midterm Exam Guide - Everything you need to know! (38 pages long)

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CHM135H1
MIDTERM EXAM
STUDY GUIDE
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CHM135 Chapter 5 Readings Study Notes
-periodic table: graph of atomic radius versus atomic number shows periodic rise and fall
pattern
5.1
-spectroscopy: the study of the interaction of radiant energy with matter
-electromagnetic spectrum: all forms of electromagnetic radiation collectively make up
the electromagnetic spectrum
-electromagnetic energy is characterized by frequency, wavelength, and amplitude
-frequency (v): the number of wave peaks that pass by a given point per unit time
(expressed in Hz, s-1)
-wavelength (λ): distance from one wave peak to the next
-amplitude: height of the wave, measured from the centre line between peak and trough
intensity of electromagnetic energy is proportional to the square of the wave amplitude
5.2
-photoelectric effect proposed by Einstein in 1905
-effect: irradiating a clean metal surface with light causes electrons to be ejected from the
metal; frequency of light used for irradiation must be above some threshold value,
different for every metal
-Einstein explained by assuming that a beam of light behaves as if it were a stream of
particles (photons) whose energy is related to their frequency of wavelength by Planck’s
postulate:   
-higher frequencies and shorter wavelengths correspond to higher energy radiation, while
lower frequencies and longer wavelengths correspond to lower energy
-if the frequency of a photon striking metal is below minimum value, no electron is
ejected
-above threshold level, sufficient energy is transferred form the photon to an electron to
overcome the attractive forces holding the electron to the metal
-work function of the metal: amount of energy necessary to eject an electron
lowest for group 1A and 2A elements (elements on the left side of the table hold
electrons less tightly and lose them more readily)
-energy of individual photon depends on frequency, not intensity of light beam
-intensity is a measure of the number of photons in a beam, while frequency is the
measure of the energies of those photons
5.3
-atoms give off light when heated or energetically excited, and emit light at certain
specific wavelengths
-line spectrum: when passed through a narrow slit and a prism, the light emitted by an
excited atom is found to consist of only a few wavelengths, giving a series of discrete
lines (unique for each element)
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-Balmer-Rydberg equation:
 
5.4
-Neils Bohr: described model of hydrogen atom as small, positively charged nucleus with
an electron circling around it; postulated that energy levels of orbits are quantized so that
only certain specific orbits corresponding to certain specific energies for the electron are
available
-explained line spectrum for hydrogen: each orbit has its own radius which is directly
related to energy; as radius increases, energy also increases
-no change in energy when an electron moves within its orbit, but when it falls into a
lower orbit or emits a photon whose energy equals the difference in the energies of the
two orbits:      
-when energy is absorbed by an atom, an electron moves form a lower to higher energy
orbit
when electron falls from higher to lower energy orbit, energy is released
-limitations to Bohr model:
1. fails to predict spectrum of any atom other than hydrogen (works only for 1 electron
species)
if more than one electron exists, electron-electron repulsion must be accounted for
2. doesn’t give accurate description of electron location
electrons don’t move in fixed, defined orbits
5.5
-de Broglie: suggested that matter is wavelike as well as particlelike:  

-human scale: never directly observed wave nature of familiar objects because
wavelengths of macroscopic objects are too small
-atomic scale: distances and masses are so tiny that light and matter behave in different
form than we’re used to
-1927: C. Davisson and L. Germer directed beam of electrons at nickel crystal, generating
a diffraction pattern
electrons travelling as waves were diffracted around nuclei in the crystal, bright and
dark areas produced by constructive and destructive interference
5.6
-1926: Schrodinger proposed quantum mechanical model of atom
-fundamental idea: concentrate on electron’s wavelike properties
-1927: Werner Heisenberg showed that it is impossible to know precisely where an
electron is and what path it follows (uncertainty principle)  

-according to equation, we can never know both the position and velocity of an electron
beyond a certain level of precision
5.7
-Schrodinger’s quantum mechanical model is in form of wave equation, solutions to
wave equation are wave functions or orbitals
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