Identifying Elements by Atomic Number – and Atomic Mass • Increase left to right 1 e2 e- Electrons in Valence Shell • Define Chemical Properties 4 e3 e- 8 eEtc. Orbit 1 Orbit 2 Orbit 3 Orbit 4 Orbit 5 Electrons in valence orbits • Define Chemical Properties Electrons around an atom can be found in different orbits Each orbit has its own energy level (compared to the nucleus) Low Energy: Close to the nucleus High Energy: Far from nucleus When energized, electrons from one energy level to a higher one around the nucleus of the atom. They emit energy in the form of electromagnetic radiation (LIGHT!) If there are an infinite number of electron jumps, a continuous atomic spectrum is created. Light energy travels in waves The wavelength of light determines the color Short Waves: HIGH Energy – FAR from nucleus Long Waves: LOW Energy – CLOSE to nucleus Prism – Breaks up white light into a rainbow of colors (a spectrum) Diffraction Grating – Glass or plastic, ruled with many finely spaced lines (like CD). When energy hits an atom, the energy is absorbed by the electrons and they become “excited” (jump to a higher orbit). When the electrons jump from the higher orbits back to lower orbits, the energy is emitted as light. These spectral lines (lines in a spectrum) are unique to each element, so can be used to identify them. TOTAL # electrons ? H=1 He = 2 Li = 3 O=8 C=6 N=7 Notice anything about the # of lines in each line spectrum? H=1 He = 2 Li = 3 O=8 C=6 N=7 Why do they have MORE lines than electrons? H=1 He = 2 Li = 3 O=8 C=6 N=7 Why are some lines brighter than others? Atomic Emission Spectrum for Unknown Star a) How does the light that astronomers see from distant stars and galaxies tell them that the same atoms with the same properties exist throughout the universe? b) Which element is not in the star that produced the “unknown spectrum”? How can you tell? When “energized”, electrons can jump up to higher energy level shells When they move back down they give off some energy as light Different wavelengths make different colors ! Let’s EXPLORE!!