Quantum Theory

Quantum Theory Explains location of electrons Bohr vs. Quantum Quantum Mechanical Model Probability Atomic Orbitals Principal energy levels Sublevels Orbitals Spin

Bohr Model Electrons travel in definite orbits around the nucleus. Planetary Model Electrons are located in energy levels Electrons can not exist between energy levels A quantum of energy is needed to move an electron from one level to the next higher level Photon: a quantum of light energy released when an electron falls an energy level

Quantum of Energy Energy is released or absorbed when an electron moves from one energy level to the next Electrons move to higher energy levels when energy is absorbed Electrons release the same quantum of energy as light when electrons fall into a lower energy level. We call this a photon of light.

Terms Ground State- Lowest energy level occupied by an electron when an atom is in its most stable configuration Excited State – Energy level occupied by an electron that is higher than the stable ground state energy level.

Quantum Mechanical Model Electrons are located in energy levels. The region is no longer a well defined orbit, but rather a 3D mathematical probability region outside the nucleus called an orbital This 3D region is also known as the electron cloud. 90% of the time the electron is expected to be in this area. A quantum of energy is still required to move an electron to a higher energy level and a photon of light is still released when the electron falls to a lower energy level

Light Both a wave and a particle Amplitude: Height from the origin to the crest Wave Length (λ ) : The distance between crests Frequency (ν) : The number of wave cycles to pass a given point per unit of time. SI units are hertz. Speed of light = wave length X frequency c = λ ν c = 3.0 X 108 m/s

A Wave                                                                            

Practice What is the wavelength of radiation with a frequency of 1.50 x 1013 s-1? Does this radiation have a longer or shorter wavelength than red light?

Max Planck Related quantized light energy to the frequency of the light wave E = hv; v is the frequency and h is Planck’s constant H= 6.6262 x10-34 J-s

Atomic Emission Spectra Every element ( in the gas or vapor state) emits light when heated  Emission spectrum for each element is unique. Like a fingerprint. Each line corresponds with one specific amount of energy being emitted Video clips

Electron Configuration

Atomic Orbitals Electrons are located in atomic orbitals. 4 distribution levels of electrons around the nucleus Principal energy level Sublevel Orbital Spin

Principal Energy Levels Defined by a principal quantum number (n) n = 1, 2, 3, 4... Distance from the nucleus increases as n increases Energy increases as n increases

Sublevels Within each principal energy level, the electrons occupy energy sublevels  The number of sublevels is the same as the principal quantum number n = 1 1s n = 2 2s, 2p n = 3 3s, 3p, 3d n = 4 4s, 4p, 4d, 4f

Orbitals the region where electrons are likely to be found  Orbitals are identified by letters and have different shapes sublevel shape number s orbitals spherical 1 p orbital dumbbell 3 d orbital cloverleaf 5   f orbital 7

Practice How many orbitals are in the following sublevels? 3p sublevel: 2s sublevel: 4f sublevel: 4p sublevel: 3d sublevel:

Spin 2 electrons occupy each orbital These 2 electrons have equal and opposite spins

Rule of Electron Configuration

Aufbau Principle Electrons enter orbitals of lowest energy first S sublevel is lowest energy sublevel

Pauli Exclusion Principle An orbital can hold no more than 2 electrons Those electrons must have opposite spin

Hund’s Rule When electrons occupy orbits of equal energy, one electron enters each orbital before the 2nd electron enters any orbital