1. Unit 4: The Atom & the Electron Configurtation James Hutchison

2. The Atom & the Electron Configurtation Atomic orbitals The regions in which electrons are likely to be found Principle Quantum numbers (n) Refers to a major energy level in an atom These principle energy levels are assigned values in order of increasing energy (n=1, n=2, n=3, and so on) The principal energy levels have a specific number of sublevels The sublevels are designated by the principle energy number and s, p, d, or f Sublevels have specific numbers of orbitals The maximum number of electrons that can occupy a principle energy level is given by the formula 2n 2, where (n) is the principle quantum number. − EX. Energy level n=3: 2(3 2 ) = 2(9) = 18 electrons

3. The Atom & the Electron Configurtation Atomic orbitals (cont) Atomic Orbitals are denoted by the letters s, p, d & f (from inner to outer) Atomic orbital shapes: s = spherical (there is 1 orbital) p = dumbbell-shaped (there are 3 orbitals) d = clover-leaf (there are 5 orbitals, but only 4 of the 5 are this shape) f = too complicated to describe. (there are 7 orbitals) The number and kinds of atomic orbitals depends on the energy sublevel Nodes are areas where the probability of finding electrons is low

4. The Atom & the Electron Configurtation Atomic orbitals (cont) http://www.uky.edu/~holler/html/orbitals_2.html S→ ← d f → ←p

5. The Atom & the Electron Configurtation Electron Configurations The ways in which electrons are arranged around the nucleus of an atom Three rules explain how to find the electron configuration of atoms Aufbau principle – e - enter the lowest energy level first Pauli exclusion principle – an atomic orbital may hold at most 2 e -. They must have opposite spins. − A vertical arrow indicates an electron and direction of spin (↑ or ↓). Hund’s rule – when e - occupy orbitals of equal energy, one e - enters each orbital until all the orbitals contain one e - with parallel spins

6. The Atom & the Electron Configurtation Shorthand Electron configurations: a. Involves writing the energy level and the symbol for every sublevel occupied by an electron. (EX. 1s) b. A superscript number indicates the number of electrons occupying that sublevel. (EX. 1s 1 ) Aufbau Diagram – the diagonal rule 14