Chemistry I Chapter 4 Arrangement of Electrons

Electromagnetic Radiation Energy that exhibits wavelike behavior and travels through space Moves at the speed of light (c) c = 3.00 X 10 8 m/s

Electromagnetic Spectrum

Photoelectric Effect This is the emission of electrons from a metal when light of high enough frequency hits the metal’s surface. Wave theory predicts that any frequency of energy could eject an electron, but this is not so.

Max Planck Said that a hot object does not emit EMR continuously as expected Energy emitted in small packets (quanta) Quantum is the minimum quantity of energy that can be lost or gained by an atom.

Planck’s Equation E = hν E is energy in Joules h = Planck’s constant X J-s ν = frequency in 1/s or Hz

Einstein Proposed that light can behave like a stream of particles, introducing the dual wave- particle nature of EMR He called this mass-less particle of light a photon which is a quantum of light energy Won Nobel Prize for photoelectric effect.

Dual Wave-Particle Nature of Light Wave theory 1.Frequency 2.Wavelength 3.Interference 4.Diffraction Particle theory 1.Photoelectric effect 2.Emission of light by hot objects 3.Line-emission spectra of elements

Hydrogen-atom Emission Line Spectrum Ground State-lowest energy state of atom (only one) Excited state-higher potential energy than ground state Hydrogen separates into 4 colors of the visible spectrum called the emission-line spectrum The attempts to explain this spectrum led to the Quantum Theory of the atom

Bohr Model

Emission of a photon

Bohr Model of Hydrogen Atom Solved hydrogen atom spectrum-1913 The electron can circle the nucleus in allowed paths or orbits. The electron has a definite fixed energy in an orbit. Emission is when the electron moves to a lower level and a photon in emitted Absorption is when the electron absorbs energy and moves to a higher level Bohr calculated allowed energy levels for hydrogen and related energy level changes to the lines in the hydrogen emission spectrum

QUANTUM MODEL OF THE ATOM Louis de Broglie -extended wave-particle description to all matter in motion Said electrons have wave-like properties and that electrons can be bent or diffracted. λ = h/mv m is mass in kg and v is velocity in m/s

Heisenberg’s Uncertainty Principle -deals with detection of electrons. It is impossible to determine simultaneously both the position and velocity of the electron. Schrodinger Wave equation- determines the probability of the electron’s location. This equation treats electrons in atoms as waves and lays the basis for modern quantum theory.

QUANTUM THEORY Mathematically describes the wave properties of electrons and other small particles and determines the probability of finding an electron. The electrons exist in regions called orbitals.

atom’s electron orbital — an atom's actual wave function! To capture the image, researchers utilized a new quantum microscope