electromagnetic radiation – transmission of energy through space in the form of oscillating waves wavelength, – distance between identical points on successive waves

frequency, ν – # times per second a wavelength moves past a point (sec) Heinrich Hertz units for v = 1 sec 1 sec = Hertz or Hz ν = 1 1 sec ν = 1 Hz

All electromagnetic radiation travels at the same velocity: the speed of light, or c. c = 3.00  10 8 m/sec · ν (m) · (1/sec) = m/sec c = ·ν

The entire electromagnetic spectrum

Max Planck Planck: “atoms absorb or release energy in ‘discrete’ (or fixed) amounts”. quantum – the smallest amount of energy an atom can absorb or release

quantized – only certain, fixed energies are allowed continuous – any energy is allowed continuousquantized

Albert Einstein Einstein: “light exists as a tiny particles” photon – the smallest particle of electromagnetic radiation (or light)

E = h ν h = Planck’s constant h = x J·sec E = energy of a photon

How much energy (in Joules) does a photon of 555 nm possess ? 1 m = 1 x 10 9 nm c = ν E = h ν E = hc

continuous spectrum – a rainbow where one color continually bleeds into the next

emission spectrum – light emitted from an excited species

Hydrogen discharge tube resulting line spectrum line spectrum – light of only certain wavelengths (or colors) are observed

The line spectrum of hydrogen The line spectrum of sodium The line spectrum of neon

Niels Bohr n distance from nucleus 153 pm 2212 pm 3476 pm 4846 pm pm quantized – restricted to certain, fixed values or places

The Bohr Model of the Atom Electrons “orbit” the nucleus at a fixed distance. The electron may have ONLY the energy of the specific orbit.

ground state – e - in atom are in the lowest energy state possible (closest to the nucleus) excited state – e - in atom are promoted to higher energy states (further from the nucleus) absorb E release E n = 1 n = 2 (or higher)

when an electron returns from the excited state back down to the ground state, it releases (or emits) energy in the form of a photon of light the wavelength (or color) of the photon is indicative (or representative of) the energy difference (or gap) between the orbitals where the transition occurred

Transitions between Quantized Levels excitation (absorb energy) emission (release energy) n = 1 n = 2

but why different photons ? ex. hydrogen has 4 different lines red photon with = 656 nm turquoise photon with = 486 nm purple photon with = 434 nm

Real Story !