Electron Configuration Peg Ellis

INTRODUCTION Modern Atomic View: The world of the atom is made up of waves and probability, The speed and location are subject to uncertainity.

ELECTRON ORBITALS Heisenberg Uncertainty Principle It is impossible to know with certainity both the location and the velocity of an electron.

Bohr Diagrams Diagrams are useful for counting electrons and illustrating different energy levels. Worthless as pictures of what atoms really look like.

This solar system model uses orbits To show where the electrons are. Electrons do not orbit the nucleus. They live in regions of space called Orbitals. Orbitals are organized by the energy level or shell that they belong to. They are clouds of probability.

An orbital is the shape of the region of space where an electron is most likely to be found. This ball-shaped orbital is hydrogen. The dots represent possible positions of the one electron hydrogen has.

Notice there are more dots near the center of sphere than near the edges. 1s orbital ANALOGY: Bird feeder on a pole with birds migrating south surrounding the feeder. Blue spots could be a bird at any given time. Spherical shape

2s Orbital Also shaped spherical. The difference: Larger and higher energy than the 1s orbital.

SHAPES OF ORBITALS 2s orbital 2p orbital 3d orbital Spherical double lobed complex There are also f orbitals- very complex

ENERGY LEVELS The more energy- the farther away the shell is from the nucleus 1 st shell=one type of orbital= s 2 nd shell = two types = s,p etc….

Principal Quantum Number The energy levels or shells are distinguished by their number. This number is called the principal quantum number. Each energy level have specific Names. N1 =only 1s orbital N2 = 2s and 2p orbitals N3= 3s, 3p, and 3d orbitals

n = 2 n = 3 n = 1 n = 4 Energy Levels

s orbitals d orbitals Number of orbitals Number of electrons p orbitals f orbitals How many electrons can be in a sublevel? Remember: A maximum of two electrons can be placed in an orbital

ELECTRON RULES Aufbau Principle – from bottom up Hund’s Rule – singles first Pauli Exclusion Principle – opposites only

From the Bottom Up: Rooms must be filled from the ground floor up. Fill the one room on the first floor before starting to put new tenants on the second floor. Then fill the s room before the p rooms. At higher floors the order might change a bit. Aufbau Principle: the electrons fill the available orbitals from lowest energy to highest energy. In the ground state all the electrons are in the lowest possible energy level.

Singles First: the owner of the building wants to have the tenants spread out as much as possible. For that reason singles are placed in rooms before couples. If couples must be placed into a room then all of the other rooms on that floor must already have a single in them. Hund’s Rule: The electrons must be placed into the orbitals in such a way that no pairs are put together unless absolutely necessary. That is, single electrons must be placed into boxes first and then paired up if necessary.

SHORTHAND NOTATION 1s 2 1 = quantum number (energy level) s= s- type orbital 2= electrons 2p 6 = 2 nd quantum number, p type orbital, 6 electrons

Electron Configurations 2p 4 Energy Level Orbital Number of electrons in the orbital 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 … etc.

Electron Configuration Order

Notice that 4s orbital fills Before the 3d orbital. This is because 4s is actually slightly lower in energy than the 3d orbitals.

Arrow direction Represents electron Spin. Clockwise and counterclockwise

What is the element? 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1

Rubidium – 37 electrons What is the element? {Kr} 5s 1