Electron Configuration

Peg Ellis

INTRODUCTION

Modern Atomic View:

The world of the atom is madeup of waves and probability,

The speed and location are subject to uncertainity.

ELECTRON ORBITALS

Heisenberg Uncertainty PrincipleIt is impossible to know

withcertainity 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 orbitsTo show where the electrons are.Electrons do not orbit the nucleus.

They live in regions of space calledOrbitals. 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 electronis most likely to be found.

This ball-shaped orbital is hydrogen.The dots represent possible positionsof the one electron hydrogen has.

Notice there are moredots near the center of sphere than near theedges.1s orbital

ANALOGY: Bird feeder on a pole with birds migrating south surrounding the feeder. Blue spots could be a birdat 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

1st shell=one type of orbital= s2nd 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 specificNames. N1 =only 1s orbital N2 = 2s and 2p orbitals N3= 3s, 3p, and 3d

orbitals

n = 2n = 2

n = 3n = 3

n = 1n = 1

n = 4n = 4

Energy LevelsEnergy Levels

s orbitalss orbitals d orbitalsd orbitals

Number ofNumber oforbitalsorbitals

Number of Number of electronselectrons

p orbitalsp orbitals f orbitalsf orbitals

How many electrons can be in a sublevel?How many electrons can be in a sublevel?

Remember: A maximum of two electrons can Remember: A maximum of two electrons can be placed in an orbital.be placed in an orbital.

1 3 5 7

2 6 10 14

ELECTRON RULES

Aufbau Principle – from bottom upHund’s Rule – singles firstPauli 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 placedinto a room then all of the other rooms on that floor must already have a single in them.

Hund’s Rule: The electrons must beplaced into the orbitals in such a way that no pairs are put together unless absolutelynecessary. That is, single electrons must be placed into boxes first and then paired up if necessary.

SHORTHAND NOTATION

1s2 1 = quantum number (energy level) s= s- type orbital

2= electrons2p6 = 2nd quantum number, p type orbital, 6 electrons

Electron Configurations

2p4

Energy LevelEnergy Level

OrbitalOrbital

Number of Number of electrons in electrons in the orbitalthe orbital

1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s22 3d 3d1010 4p 4p66 5s 5s22 4d 4d1010 5p 5p66 6s6s22 4f 4f1414…… etc.etc.

Electron Configuration Order

Notice that 4s orbital fills Before the 3d orbital.

This is because 4s is actuallyslightly lower in energy than the 3d orbitals.

Arrow directionRepresents electronSpin. Clockwise and counterclockwise

What is the element?

1s22s22p63s23p64s23d104p65s1

Rubidium – 37 electrons

What is the element?

{Kr} 5s1