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Chapter 6 Review and Breathe The Wave Nature of Light • Electromagnetic radiation is one way energy travels through space. • Wavelength is inversely proportional to frequency • =c/ The Particle Nature of Light • Energy is gained or lost in whole number multiples. • ΔE=nh • This energy is Quantized. • Electromagnetic radiation is quantized as photons. Dual Nature of Light • • • • • • • Photons have energy of Ephoton = hc/ Energy is also E=mc2 (c=speed of light) Thus: m=E/c2 Substitute E=hc/ in the above equation m=hc/c2 And finally: m=h/c Light acts as a wave and has mass Do particles have wave characteristics? • If a photon has mass m=h/c while it is moving… • Then a particle moving at a velocity v has a wavelength using the equation m=h/v • Solve for and =h/mv • This is de Broglie’s equation. Atomic spectrum of Hydrogen • When light is passed through a prism one gets an emission spectrum. • When all wavelengths are possible one gets a continuous spectrum. • When energy is quantized the spectrum is a line spectrum, or discrete. How do electrons emit light? The Bohr model • Bohr proposed that in a hydrogen atom the electron orbits the nucleus in allowed circular orbits. • Each orbit has an energy associated with it. • E=-2.178x10-18J (Z2/n2) Quantum Mechanical Model • Bohr’s model doesn’t work for atoms larger than hydrogen. • Electrons are not behaving in a manner that agrees with the circular orbit model. Wave function • Electrons in the higher energy levels are acting more like standing waves than like particles. • Schrödinger looked at the wave function of the electron. This wave function describes the electron’s orbital. But where is the electron? • Heisenberg’s uncertainty principle states that we cannot know with certainty both how fast an electron is moving and where it is. • Δx * Δ(mv)> h/4 • Probability distribution Quantum numbers • each energy level is designated by the value n which is an integer from 1 (lowest energy or "ground state") on up • the number of types of orbitals possible on an energy level is also equal to n • the maximum number of actual orbitals on an energy level is equal to n2 • the maximum number of electrons in an orbital is equal to 2 • the maximum number of electrons on an energy level is equal to 2n2 Quantum numbers • Principle quantum number, n=integral values 1, 2, 3 … Represents the energy level. • Angular quantum number, l = 0, 1, 2 etc for n-1. It represents the shape of the orbital. • Magnetic quantum number m= -l to l. It is related to the orientation of the orbital in relationship to other orbitals in the atom. Pauli Exclusion Principle • In given atom, no two electrons may have the same set of quantum numbers. This is known as the Pauli Exclusion Principle. • Since each orbital may hold up to two elections. Each election is assigned a separate spin. • +½ and -½ Summary Table Angular quantum numbers Take note of the nodes! • For l= 0, 1, 2, and bottom row 3. Aufbau Principle • As protons are added to a nucleus to build up elements, electrons are added too. • These electrons are added into the lower energy orbitals first. Hund’s Rule • The lowest energy configuration In an orbital is one having the maximum number of unpaired electrons allowed by the Pauli Principle in a set of degenerative orbitals. Electron Configuration and the Periodic Table • Elements’ reactivity is based on its valence electrons. • The periodic table demonstrates the valence electrons of each group.