Electrons in Atoms

Atomic Models Atomic models are always changing The model that was used in chapter 5 is obsolete

Contributions to the Model John Dalton – Atoms were indivisible Change – discovery of subatomic particles J.J. Thomson – discovered electrons Change – discovery of nucleus Ernest Rutherford – discovered nucleus Change – orbit of electrons Niels Bohr – Claimed electrons orbit nucleus in various “energy levels” Change – probability of finding electrons Schödinger – The probability of finding an electron is represented by a cloud

Quantum Mechanics Schödinger represents the probability of finding electrons on a certain energy level This is a “s” sublevel Where the electrons are located in relationship to the nucleus is called the Atomic Orbital

Atomic Orbitals S orbit S orbits can hold a maximum of 2 electrons Alkali metals and alkaline earth metals are s-orbits

Atomic Orbitals P orbit P orbits can hold a maximum of six electrons Nonmetals, Metalloids, and Noble Gases are p-orbits Note: they also contain the s-orbit

Atomic Orbitals D orbit D orbits can hold a maximum of ten electrons Transition metals are d- orbits Note: they also contain s and p-orbits

Energy Levels Energy levels are represented with the letter “n” The lowest energy level n = 1 Energy levels can hold only so many electrons n = 1 2 n = 2 8 n = 3 18 n = 4 32

Electron Configurations How electrons are configured around a nucleus Three rules explain how to determine the configuration

Aufbau principle Electrons enter orbitals of lowest energy first Increasing Energy Level

Pauli Exclusion Principle An atomic orbital may describe at most two electrons The electron pair must have opposite spins Empty One Two

Hund’s Rule When electrons occupy orbitals of equal energy, one electron enters each orbital until all orbitals contain one electron with parallel spins

Hund’s Rule P-orbital

Exceptions Not all elements follow the basic electron configuration rules Chromium Following rules 1s22s22p63s23p63d44s2 Correct 1s22s22p63s23p63d54s1 Copper Following rules 1s22s22p63s23p63d94s2 Correct 1s22s22p63s23p63d104s1

Cont. Half and full subshells are more stable than partially filled levels The half filled 4s sublevels are stable