emission and absorption spectra

Alternative transcript:

visible wavelengths is called white light. All atoms and molecules absorb light of certain wavelengths. Therefore, when white light is passed through the rapour of an element, certain wavelengths will be absorbed by the atoms and removed through the light. Looking through a spectrometer, black lines appear in the spectrum where light of some wardengths has been absorbed. The wavelengths of these lines correspond to the energy taken in by the atoms to promote electrons from lower to higher energy levels. increasing wavelength. EMISSION SPECTRA when atoms are given energy by heating or by an electrical field, electrons are excited and the additional energy promotes them from a lover energy level to a higher one when the source of energy. is removed and the electrons leave the excited state, they fall from the higher energy level to a lower energy level and the energy lost is released as a Photon ( quantum of light overgy) with a specific frequency. The observed spectrum consists of a number of coloured lines on a black background nconig 1=40=2 4th 3rd 2nd 7:34912 118 transition-Balmer waretengre The fact that only certain colours appear in an atom's emission spectrum means that only photons having certain energies are emitted by the atom If the electron energy levels were not quantised but could have any value, a continuous spectrum rather than a line. spectrum would result. EMISSION SPECTRA Lowest energy lowest frequency Highest wardengen Red line λ = 656 nm to find energy E=hc λ E-6-63x10-34 x 3.00×108 656 x 10-9 E = 3·03x10-19 J Absorption Spectra: electrons. promoted I absorb energy and are to a higher energy level. ATOMIC ABSORPTION Electrons absorb energy - move to a higher energy level. ATOMIC EMISSION Excited elections fall to a lower energy. level and emit a photon Discrete lines. F=hf 4 = C/₂ E = n²/₂ - energy levels have fixed values transitions between correspond to same f. ↑ E= 14 ↑ f = la 4 E=LA ATOMIC EMISSION 475 450 400 300 100 SALMER SERIES (n=2) visible region LYMAN SERIES (n=1) UV region Atomic Emission: excited electron falls to a lower energy level and emits a photon.. CONVERGence limit n=1 to 11=00 2 = 92nm calculate 1 ie. E = no E = 2.16 × 10-15 J KJ mat E = 663x1024 x 3:00×108 92 x 104 Avogadro constant NA 6-02 x 1028 mol-1 PASCHEN SERIES (1:3) IR = 2.16 x 10-18 J x NA = 1301498 Jmo +1000=1301 KJ met n=∞ n=1 1:0 1=6 n=5 904 n=3 ・1=2