Features of Waves (3.1)
Electromagnetic radiation
a wave that travels at the speed of light
the electric field is the sine wave and is measured in voltage
magnetic field is the cosine wave
quantized waves
fixed ends of stationary wave restrict number and types of waveforms
only discrete values of a continuous set are allowed
node - region where amplitude is zero
no motion
Energy, wavelength, frequency of a photon (3.1)
wavelength goes in the opposite direction of frequency and energy
frequency is represented by v
wavelength is represented by lambda
the visible light spectrum is 400-800nm
blue is 400nm and red is 800nm
https://www.cyberphysics.co.uk/graphics/diagrams/waves/EMSpectrumcolor.png
one photon is equal to one light unit
Energy is measured in joules
Photoelectric effect (3.1)
minimum threshold to eject electrons is related to the frequency of light
classical physics suggested the amplitude of a wave influences the energy but experimentally, it was discovered that it is the frequency
there is a certain amount of energy required to hold the atom together
in order to eject an electron, you must overcome the threshold energy
Orbit energy of e-, delta E, Bohr Model (3.1, 3.2)
line spectra
elements and molecules have emission spectra that correspond to a series of line
each line is a single wavelength
Rydberg equation (included in sheet)
n refers to which orbit an electron might be in
1 over lambda
https://i.stack.imgur.com/oDIES.jpg
wave particle duality
light behaves both wavelike and particle-like
wavelike property - interference patterns obtained when light passed through a double slit
particle like property - photoelectric effect
Bohr's atomic theory
Bohr used the results of Planck and Einstein's experiments to develop a better atomic theory, making the following assumptions about an atom's electrons
electrons travel in circular orbit around the nucleus
energy proportional to distance
orbits are quantized
equation is included on the sheet
E sub n
Delta E
Z is the nuclear charge
energy is absorbed/emitted when orbits change
Orbit transitions
an electron moves to a higher level (n) when a specific quantity of energy is absorbed
an electron moves to a lower level (n) when a specific quantity of energy is emitted
the Bohr model fails with more than one electron, but was right about the following
e- attracted to nucleus by the opposing charges of the particles
e- energies are quantized
e- energies increase as the distance from the nucleus increases
discrete energies in spectra of elements result from quantized energy transitions of e- between levels
DeBroglie Wavelength (3.3)
wavelength is equal to h over linear momentum
linear momentum is equal to mass multiplied by velocity
quantization of angular momentum, L, is equal to n multiplied by h
wavelike properties are only important for small particles (electrons)
Electron location and momentum
Heisenberg Uncertainty Principle
We can only know either the position or momentum of a particle at any given instant
we can not know both in one instant
consequence of wave-particle duality
there are limitations governing the motions of quantum particles
schrodinger
expanded on de Broglie's work and developed a wave equation that described and electron as a wave function, represented by psi
psi are not physical waves but complex probability amplitudes
psi squared is equal to the probability distribution (e- distribution)
Quantum Theory, Quantum Numbers (3.3)
a series of four quantum numbers describe the energies, locations and other properties of an electron in a given atom
principle quantum number (n)
discrete energy level
energies increase as the distance from the nucleus increase
atomic orbital
which orbital
corresponds to the row on the periodic table
angular momentum quantum number (l)
shape
integers from 0 to n-1
s, p, d, and f orbitals are 0, 1, 2, and 3, respectively
when l is not equal to 0, the orbitals have directionality about the z axis described by the magnetic quantum number
magnetic quantum number (m sub l)
orientation
integers from -l to l
number of degenerate orbitals in subshell
spin quantum number (m sub s)
electronic spin
overall one magnitude, two quantized states
+1/2, -1/2
spin states degenerate unless in external magnetic field
Orbitals and Wave functions (3.3)
pauli exclusion principle
no two electrons can have the same two sets of electrons
they have different quantum numbers in some way or another
radial nodes
there are certain distances from the nucleus at which the probability density of finding an electron located at a particular orbital is zero
the number of nodes is equal to the energy level minus l minus 1
Electron Configurations (3.4)
the total number of electrons in an atom populate these orbitals following a set of rules
the end result is an electron configuration or orbital diagram
hund's rule
electrons spread out within a sub shell and have the same spin
filled and half filled subshells are especially stable
aufbau principle
build up from lowest energy to highest
valence electrons
the electrons in the outermost principle quantum level of an atom (largest value of n)
the 3de- are not counted as part of the valence shell
full d and f shells are not considered part of the valence shell because they are not involved in reactions if they are full
therefore, determination of the number of valence e- for any main group atom is simply the group number
HOWEVER, atoms in the transition series do count the de- toward the valence shell
Periodic Trends (3.5, 3.6)
periodic law - the properties of the elements are periodic functions of their atomic numbers
nuclear charge
many of the periodic trends involving e- can be qualitatively explained using the effective nuclear charge (Z sub eff) of the atom
this is the pull exerted on a specific electron by the nucleus, taking into account any electron-electron repulsions
Z sub off is equal to Z minus the shielding
shielding is the e- repulsions
radii
covalent radius - one half the distance between the nuclei of two identical atoms when they are joined by a covalent bond
ionic radius - size of an ion
increases as you go down and to the left
ionization energy - Energy required to remove the most loosely bound e- in formation of cation
as size increases, IE decreases
it becomes easier to remove electrons
increases as you go up and to the right
watch for filled and half filled subshells
electron affinity - energy change for adding an electron to gaseous atom in formation of an anion
increases going up and to the right
unit prefixes and conversions
pico 10^-12
nano 10^-9
micro 10^-6
milli 10^-3
centi 10^-2
kilo 10^3
Ionic and Covalent Bonds, including polyatomic (3.7)
monatomic ions
the majority of chemical reactions do not change the nucleus of an atom
electrons can be transferred or shared
groups
alkali metals
alkaline earth metals
chalcogens
halogens
noble gases
polyatomic ions
usually have a negative charge
binary bonding
ionic
metal and nonmetal
groups of atoms held together by electrostatic interactions
transfer of electrons
molecular/covalent
nonmetal and nonmetal
groups of atoms held together by sharing electrons