Mullis Chemistry Holt Ch.41 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 Chemistry Holt Ch.42 Example: Building electron configurations for the ground state of an atom Phosphorous: 15 electrons: Start with 1s. Each s can hold 2 electrons. Each p can hold 6 electrons. Place one electron per orbital, then pair until that level is full. Only then go to the next level.

Electron Movement Light When an electron absorbs a quantum of energy, it can be excited to a higher energy level than its ground state. When the electron falls back to a lower level, it emits energy as a photon. 3

Mullis Chemistry Holt Ch.44 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.

The Bohr Atomic Model Bohr proposed that an electron ORBITED the nucleus at specific levels. Bohr studied hydrogen to explain its emission line spectrum. 5

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Mullis Chemistry Holt Ch.47 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 Chemistry Holt Ch.48 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.