Atomic Structure & Periodicity Chapter 7

EM Radiation EM – electromagnetic Wavelengths measured in meters

Properties Energy decreases  Frequency decreases  Wavelength increases  Speed is constant  2.9979 x 108 m/sec

Properties Relationship Wavelength (λ) Frequency (ν) Speed (c) Distance between two consecutive peaks or troughs in a wave Measured in m Frequency (ν) Number of waves that pass a given point per second Measured in hertz Hz = sec-1 Speed (c) Measured in m/s Relationship λ ν = c

Nature of Matter Max Planck & Quantum Theory Energy is gained or lost in whole number multiples of the quantity hν Frequency = ν Planck’s constant = h = 6.626 x 10-34 Js ΔE = hν Energy is transferred to matter in units of energy called quanta Einstein and the Particle Nature of Matter EM radiation is a stream of particles – photons Photon – “packet” of EMR energy Ephoton = hν = hc/λ Energy and mass are inter-related E = mc2

Nature of Matter de Broglie and the Dual Nature of Light Light travels through space as a wave Light transmits energy as a particle Particles have wavelength, exhibited by diffraction patterns Large particles have very short wavelengths All matter exhibits both particle and wave properties EMR e- Baseball Wave Wave/Particle Particle

Atomic Spectrum of H Continuous spectra Bright line spectra Contains all wavelengths of light Bright line spectra Excited electrons in an atom return to lower energy states Energy is emitted in the form of a photon of definite wavelength Definite change in energy corresponds to Definite frequency Definite wavelength ΔE = hν = hc/λ Only certain energies are possible within any atom

Bohr Model (Niels Bohr 1913) Quantum Model The electron moves around the nucleus only in certain allowed circular orbits Bright line spectra confirms that only certain energies exist in the atom Atom emits photons with definite wavelengths when the electron returns to a lower energy state Energy levels available to the electron in the hydrogen atom ΔE = -2.178 x 10-18 J (Z2/n2) n = an integer Z = nuclear charge J = energy in joules

Bohr Model Calculating the energy of the emitted photon Calculate electron energy in outer level Calculate electron energy in inner level Calculate the change in energy (ΔE) ΔE = Efinal – Einitial

( ) Bohr Model Energy Change in Hydrogen Atoms Calculate energy change between any two energy levels ΔE = -2.178 x 10-18 J 1 - 1 n2final n2initial Shortcomings of the Bohr Model Bohr’s model does not work for atoms other than hydrogen Electrons do not move in circular orbits ( )