# Wave Description of Light

## Presentation on theme: "Wave Description of Light"— Presentation transcript:

Wave Description of Light
Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space Wavelength (λ) Distance between corresponding points on adjacent waves. Unit: nm,cm,m Frequency (ν) Number of waves that pass a specific point in a given time Unit: Hz or waves/sec Recall that Speed = Distance/time (m/sec) Speed of light (c) C = λ ν Mullis

Behavior of Light Photoelectric effect Quantum
The emission of electrons when light shines on the metal Scientists found that below a certain frequency, no electrons were emitted. Light also behaves as a particle: Since hot objects do not emit em energy continuously, they must emit energy in small chunks called quanta. Quantum Minimum quantity of energy that can be gained or lost by an atom Mullis

Light as a particle and a wave Planck and Einstein
Max Planck: Relationship between quantum of energy and wave frequency Planck’s constant h = x J-s E = hν E is energy, ν is frequency Albert Einstein: Established dual wave-particle nature of light 1st Einstein explained PE effect by proposing that EM radiation is absorbed by matter only in whole numbers of photons. Electron is knocked off metal surface only if struck by one photon with certain minimum energy. Mullis

Louis de Broglie Louis de Broglie answered this. His equation:
Because we know that light has a particle nature, we might ask if matter has wave nature. Louis de Broglie answered this. His equation: λ = h/mv Lambda is a wave property. Momentum (mass x velocity) is a particle property. In one equation, de Broglie summarized the concepts of waves and particles as they apply to high-speed, low mass objects. Results of de Broglie’s discovery include X-ray diffraction and electron microscopy techniques used to study small objects. Mullis

Quantum Theory Ground state: An atom’s lowest energy state
Excited state: Higher potential energy than ground state. Photon: A particle of electromagnetic radiation having zero mass and carrying a quantum of energy (i.e., packet of light) Only certain wavelengths of light are emitted by hydrogen atoms when electric current is passed through—Why? Mullis

Niels Bohr links hydrogen’s electron with photon emission
Bohr proposed that an electron circles the nucleus in allowed orbits at specific energy levels. Lowest energy is close to nucleus Bohr’s theory explained the spectral lines seen in hydrogen’s line emission spectrum, but it did not hold true for other elements. Mullis

Arrangement of Electrons in Atoms
Principles of electromagnetic radiation led to Bohr’s model of the atom. Electron location is described using identification numbers called quantum numbers. Rules for expressing electron location results in a unique electron configuration for each element. Mullis

Building electron configurations for the ground state of an atom
Aufbau: Lowest energy level 1st Pauli Exclusion: Only 2 e- per orbital, opposite spin Hund: One electron per orbital until that level is full (same spin) 1s 3s 2s 4s 3p 2p 4p 3d Mullis

Mullis

p6 s1 s2 p1 p2 p3 p4 p5 d1 d2 d3 d4 d5 d6 d7 d8 d9 f1 f2 f3 f4 f5 f6
Sc 4 4d Y 5 5d La 6 6d Ac f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14 4f 5f

Quantum Numbers Principal quantum number, n
Angular momentum quantum number, l Magnetic quantum number, ml Spin quantum number, ms Mullis

Azimuthal quantum number = Angular momentum quantum number
Depends on the value of n Values of l starts at 0 and increases to n-1 This number defines the shape of the orbital. Orbital l s 0 p 1 d 2 f 3 Mullis

Magnetic quantum number
Magnetic quantum number is the orientation of an orbital around the nucleus. It is the number of orbitals in a sublevel. The s sublevel has 1 orbital. The p sublevel has 3 orbitals. The d sublevel has 5 orbitals. The f sublevel has 7 orbitals. Orbitals per sublevel s 1 p 3 d 5 f 7 Mullis

Magnetic quantum number, ml
Gives the 3d orientation of each orbital. Has value from –l to + l Example: 3p refers to orbitals with n = 3 and l = 1. Values of ml = -1,0,1 These three numbers correspond the 3 possible orientations of the dumbbell-shaped p orbitals (x,y and z axis). Mullis

Quantum numbers 1s ____ 2s ____ 2p ____ ____ ____ 3s _____
Magnetic quantum number Principal quantum number Angular momentum quantum number Mullis

Quantum numbers 1s ____ 2s ____ 2p ____ ____ ____ 3s _____
ms = -1/2 ms = +1/2 ml =0 ml = -1 ml = +1 Magnetic quantum number Principal quantum number Angular momentum quantum number [ for a p orbital, l = 1] Mullis