Mullis1 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.

Mullis2 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

Mullis3 Behavior of Light Photoelectric effect –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

Mullis4 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 = hνE is energy, ν is frequency Albert Einstein: Established dual wave-particle nature of light 1 st –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.

Mullis5 Louis de Broglie 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.

Mullis6 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?

Mullis7 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.

Mullis8 Quantum Numbers Principal quantum number, n Angular momentum quantum number, l Magnetic quantum number, m l Spin quantum number, m s

Mullis9 Azimuthal quantum number = Angular momentum quantum number Orbital l s 0 p 1 d 2 f 3 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.

Mullis10 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 s1 p3 d5 f7

Mullis11 Quantum numbers 1s ____ 2s ____2p ____ ____ ____ 3s _____ Principal quantum number Magnetic quantum number Angular momentum quantum number

Mullis12 Quantum numbers 1s ____ 2s ____2p ____ ____ ____ 3s _____ Principal quantum number Magnetic quantum number Angular momentum quantum number [ for a p orbital, l = 1] m l =0 m l = -1m l = +1 m s = -1/2 m s = +1/2

Mullis13 Magnetic quantum number, m l 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 m l = -1,0,1 These three numbers correspond the 3 possible orientations of the dumbbell-shaped p orbitals (x,y and z axis).