Chapter 11 Notes Electrons in Atoms: Modern Atomic Theory

5.1 Light and Quantized Energy Rutherford’s nuclear model lacking –didn’t account for electron arrangement –couldn’t explain why diff. elements behave diff. Elements emit visible light when heated in a flame

Wave Nature of Light Electromagnetic radiation – form of energy that exhibits wavelike behaviors as it travels through space (visible light, microwaves, X-rays) –Speed –Wavelength (λ) – distance b/t two crests or troughs –Frequency (ƒ) – number of waves that pass a given point in one second; measured in Hz –Amplitude – height of wave from origin to crest or trough

Electromagnetic Spectrum Encompasses all forms of electromagnetic radiation

Particle Nature of Light Max Planck –Explained emission of light by heated objects (red hot ) –Quantum – minimum amount of energy gained/lost by an atom –E quantum = h  Photoelectric effect (explained by Einstein) –Photoelectrons emitted from metal’s surface –Electromagnetic radiation is both wavelike & particlelike –Photon – particle of electromagnetic radiation w/ no mass that carries a quantum of energy

Atomic Emission Spectra Set of frequencies of the electromagnetic waves emitted by atoms of an element An element’s “fingerprint”

5.2 Quantum Theory and the Atom Neils Bohr –Danish physicist –Proposed quantum model that explained why emission spectra were discontinuous

Bohr Model of the Atom Ground state – lowest allowable energy state of an atom –Electrons orbit the nucleus in certain energy levels (circular orbits) –Smaller the orbit → lower the energy, & vice versa Excited state – electrons move to higher energy levels when the atom gains energy –Photon emitted when electrons falls back to ground state

Quantum Mechanical Model Bohr model determined incorrect –Only worked for hydrogen –Did not account for chemical behavior Louis deBroglie proposed electron wave-particle duality –All moving particles exhibit wave-like characteristics Heisenberg Uncertainty Principle – it is impossible to know both the velocity and position of a particle at the same time (He balloon)

Quantum Model… Erwin Shrödinger – Austrian physicist; using complex equation, developed quantum mechanical model (electron cloud) of the atom –Electrons treated as waves –Electrons not in circular orbits –Mathematically predicts probable location of an electron

Quantum numbers Every electron designated 4 quantum numbers –Principal quantum number (n): energy level –Sublevel (s, p, d, f) –Orbital – 3D region around nucleus that describes electron’s probable location –Spin Diff. orbitals have diff. shapes

Orbital Shapes

First four energy levels… Energy Level (n) SublevelOrbitals# of e - Total # of e - in energy level (2n 2 )

Electron configuration Arrangement of electrons in an atom Aufbau principle – each electron occupies the lowest energy orbital available –All orbitals w/i an energy level are of equal energy (ie: 2p x = 2p y = 2p z, etc.) –All sublevels w/i an energy level have diff. energies (ie 2p > 2s, etc.) –Sublevels increase in energy according to s < p < d < f. –Orbitals of one sublevel may overlap those in another energy level.

Orbital filling…

Electrons Filling…

Write electron configurations for the first 10 elements. ElementElectron Configuration Orbital NotationElectron Dot Diagram Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon

Orbital Notation Pauli exclusion principle – only two electrons with opposite spins can occupy an orbital Hund’s rule – single electrons with the same spin must occupy each equal energy orbital before electrons can be paired How to… –Draw line for each orbital s: 1 p: 3 d: 5 f: 7 –Draw arrow for each electron –Follow Pauli’s & Hund’s rules

What element is it?

Write orbital notations for the first 10 elements. ElementElectron Configuration Orbital NotationElectron Dot Diagram Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon

Electron Dot Formulas Valence electron – electron in an atom’s highest energy level Identified by an element’s group number No element has more than eight Transition metals have either 1 or 2 Group ## valence e

Electron Dot Formulas… Draw one dot for each valence electron

Write electron dot diagrams for the first 10 elements. ElementElectron Configuration Orbital NotationElectron Dot Diagram Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon