LIGHT AND THE ELECTROMAGNETIC SPECTRUM Electromagnetic energy light is characterized by WAVELENGTH FREQUENCY and AMPLITUDE Wavelength symbol is upside down y called lambda is the distance between successive wave peaks Frequency v is the number of wave peaks that pass a given point per unit time Amplitude is the height of the wave maximum from the center HIGHER frequency LOWER wavelength Wavelength lambda x Frequency v Speed c Speed of light c 3 00 x 10 8 m s Line Spectrum A series of discrete lines on an otherwise dark background as a result of light emitted by an excited atom Johann Balmer in 1885 discovered a mathematical relationship for the four visible lines in the atomic line spectra for hydrogen 1 lambda R 1 2 2 1 n 2 Johannes Rydberg later modified the equation to fit every line in the spectrum of hydrogen 1 lambda R 1 m 2 1 n 2 Rydberg constant R 1 097 x 10 2 nm 1 Photoelectric Effect Irradiation of clean metal surface with light causes electrons to be ejected from the metal Furthermore the frequency of the light used for the irradiation must be above some threshold value which is different for every metal E hv h Planck s constant 6 626 x 10 34 Joules x seconds Electromagnetic energy light is quantized PARTICLE PROPERTIES OF ELECTROMAGNETIC ENERGY Niels Bohr purposed in 1914 a model of the hydrogen atom as a nucleus with an electron circling around it In the model the energy levels of the orbits are quantized so that only certain specific orbits corresponding to certain specific energies for the electron are available Louie de Broglie in 1924 suggested that if LIGHT can behave in some respects like matter then perhaps matter can behave in some respects like light In other words perhaps matter is wavelike as well as particle like lambda h mv The de Broglie equation allows the calculation of a wavelength of an electron or of any particle or object of mass m and velocity v In 1926 Erwin Schrodinger proposed the quantum mechanical model of the atom which focuses on the wavelength of the particle In 1927 Werner Heisenberg stated that is is impossible to know where an electron is and its path a statement called the Heisenberg uncertainty principle change in X change in Mass x Velocity less than or equal to h 4pi A wave function is characterized by three parameters called quantum numbers n l m Note wave equation describes the motion of electrons as waves Solution of this equation for particular atom are wave functions or orbitals The exact electron position is not known Heisenberg Uncertainty Principle but wave functions orbital specifies where it is most probably known PRINCIPLE QUANTUM NUMBER Describes the size and energy level of the orbital Commonly called a shell Positive integer number As the value of n increases The energy increases The average distance of the e from the nucleus increases ANGULAR MOMENTUM QUANTUM NUMBER Defines the 3 D shape of the orbital Commonly called a subshell There are n different shapes for orbitals If n 1 then l 0 If n 2 then l 0 or 1 If n 3 then l 0 1 or 2 Commonly referred to by letter subshell notation l 0 s sharp l 1 p principal l 2 d diffuses l 3 f fundamental MAGNETIC QUANTUM NUMBER Defines the spatial orientation of the orbital There are 2l 1 values of mI and they can have any integral value from l to l If l 0 then mI 0 If l 1 then mI 1 0 or 1 If l 2 then mI 2 1 0 1 or 2 SHAPES OF ORBITALS Node a surface of zero probability for finding the electron