Electromagnetic spectrum Electromagnetic radiation energy that exhibits wavelike

Electromagnetic spectrum Electromagnetic radiation: energy that exhibits wave-like behavior as it travels through space

How are wavelength and frequency related? • • • Wavelength (λ) : the distance between corresponding points on adjacent waves (measured in meters) Frequency (ν) : the number of waves that pass a given point in a specific time, usually one second (measured in 1/s, s-1, Hz) Speed of light (c) = 3. 0 x 108 m/s c=λν

Photoelectric Effect Photoelectric effect: refers to the emission of electrons from a metal when light shines on the metal Ex. heating a piece of iron grey at room temp. → red → blue However, energy (light) is only observed when a certain frequency of light was used

The Particle Description of Light � German physicist, Max Planck suggested that the objects emits energy in quanta of energy. quantum: the minimum quantity of energy that can be lost or gained by an atom.

The Particle Description of Light (cont. ) • Max Planck proposed the following relationship between a quantum of energy and the frequency of radiation: E = hν • E = the energy, in joules, of a quantum of radiation, • ν = the frequency, in s− 1, of the radiation emitted • h = a fundamental physical constant now known as Planck’s constant; h = 6. 626 × 10− 34 J • s.

The Particle Description of Light (cont. ) �A photon is a particle of electromagnetic radiation having zero mass and carrying a quantum of energy. Ephoton = hν

How is light produced in a neon tube? � When a current is passed through a gas, the atoms gain energy and electrons “jump” from their ground state to a higher excited state. • The lowest energy state of an atom is its ground state. • A state in which an atom has a higher potential energy than it has in its ground state is an excited state.

The Hydrogen Atom • The four bands of light were part of what is known as hydrogen’s atomic (line) emission spectrum. • Every element has a unique atomic emission spectrum (a “fingerprint”)

Hydrogen’s Atomic Emission Spectrum

Absorption and Emission Spectra

Bohr Model of the Atom An electron can circle the nucleus only in allowed paths, or orbits • Energy must be added in order to move an electron from a lower energy level to a higher energy level. This process is called absorption. • When an electron falls to a lower energy level, a photon is emitted, and the process is called emission.

The Heisenberg Uncertainty Principle • The Heisenberg uncertainty principle states that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle.

Quantum Mechanical Model of an Atom � In 1926, Austrian physicist Erwin Schrödinger developed an equation that treated electrons in atoms as waves • Electrons do not travel around the nucleus in neat orbits, but they exist in certain regions called orbitals • An orbital is a 3 D region around the nucleus that indicates the probable location of an electron (“fuzzy cloud”)

electron configuration: the arrangement of electrons in an atom Noble Gas Notation: Uses the symbol of a noble gas followed by the electron configuration of the outer electrons

Periodic Table

Rules Governing Electron Configurations: • Aufbau Principle: electrons are added one at a time to the lowest energy orbitals available (aufbau = “building up”) • Hund’s Rule: electrons occupy equal energy orbitals one at a time before pairing up • Pauli Exclusion Principle: an orbital can hold a maximum of two electrons, each with an opposite spin direction

Orbital Diagrams An unoccupied orbital is represented by a line (or a box), with the orbital’s name written underneath the line. �An orbital containing one electron is represented as: �An orbital containing two electrons is represented as:

Valence electrons: outermost electron in an atom Electron dot diagrams (structures): Element symbol surrounded by dots representing the atoms valence electrons Ex.