Section 4.3—Electron Structure

The E-Config Hotel

The managers of this hotel are Aufbau, Hund , and Pauli. Parking Garage Shopping Center Restaurant The managers of this hotel are Aufbau, Hund , and Pauli. You are an employee who works at the hotel. When placing guests in their rooms, you MUST follow the rules!

How the Electron Hotel Fills p d Restaurant Shopping Center Parking Garage Rules: “From the Bottom Up”: Rooms must be filled from the ground floor up (meaning you must fill the floors from lowest to highest). Fill the one room on the first floor before starting to put new guests on the second floor. Then fill the s room before the p rooms. Therefore, you must fill each room with two people before moving to the next floor. “Singles First”: The manages of the hotel want to have the guests spread out as possible. For that reason, singles are placed in rooms before couples. This means that you place one person in each room, then go back and fill the rooms with the left over people. (**Remember ONLY TWO people per room!) “Opposite Gender Only”: When two people are placed in a room, they must be of OPPOSITE genders. No men may room together and no women may room together. This is just an arbitrary rule the owners made!

Another Example f p s d Restaurant Shopping Center Parking Garage If 8 people come to the hotel, where would you put them? If 21 people come to the hotel, where would he put them?

f p d s Restaurant Shopping Center Parking Garage Remember! s BEFORE p, because lower in energy! Remember! the further away from the ground (nucleus), the more energy! Remember! Guests (electrons) want to be in the lowest energy level possible!

Where do electrons really live?

Electron Clouds They don’t live in a hotel…They are in the area outside of the nucleus where the electrons reside.

Principal energy levels Electron Clouds Electron cloud Electron Hotel Which section of the hotel Which floor Which room The electron cloud is made of energy levels (s,p,d,f) Principal energy levels Subshells Energy levels are composed of subshells (1,2,3,4 …) Orbitals Subshells have orbitals.

Subshell versus Orbital Subshell – A set of orbitals with equal energy Orbital – Area of high probability of the electron being located. Each orbital can hold 2 electrons

Electron Configuration

What are electron configurations? They show the grouping and position of electrons in an atom. The number and configuration of electrons determines how something glows…so it’s important to know “where the electrons live” for an atom! Electron configurations use boxes for orbitals and arrows for electrons.

Energy and Subshells 6p 5d 4f 6s 5p 4d 5s 4p 3d 4s 3p 3s 2p Subshells are filled from the lowest energy level to increasing energy levels. 2s Energy Does this look familiar? Electron Hotel! 1s

Aufbau Principle The first of 3 rules that govern electron configurations Aufbau Principle: Electrons fill subshells (and orbitals) so that the total energy of atom is the minimum 1 What does this mean? Electrons must fill the lowest available subshells and orbitals before moving on to the next higher energy subshell/orbital. Where did we see this “rule” in the Electron Hotel?

Hund’s Rule Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up. 2 How does this work? If you need to add 3 electrons to a p subshell, add 1 to each before beginning to double up. Where did we see this “rule” in the Electron Hotel?

Pauli Exclusion Principle Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins. 3 “Spin” describes the angular momentum of the electron “Spin” is designated with an up or down arrow. How does this work? If you need to add 4 electrons to a p subshell, you’ll need to double up. When you double up, make them opposite spins. Where did we see this “rule” in the Electron Hotel?

Determining the Number of Electrons Charge = # of protons – # of electrons Atomic number = # of protons Example: How many electrons does Br-1 have?

Writing Electron Configurations Aufbau Principle: Electrons fill subshells (and orbitals) so that the total energy of atom is the minimum 1 2 Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up. Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins. 3 Remember- determine the NUMBER of electrons before configuring! Example: Write the boxes & arrows configuration for Cl

Writing Electron Configurations Aufbau Principle: Electrons fill subshells (and orbitals) so that the total energy of atom is the minimum 1 2 Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up. Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins. 3 Example: Write the boxes & arrows configuration for Cl No charge written  Charge is 0 Atomic number for Cl = 17 = # of protons 0 = 17 - electrons Electrons = 17 4 13 12 11 14 15 8 17 16 10 9 1 2 5 3 6 7 1s 2s 2p 3s 3p

Spectroscopic Notation

Spectroscopic Notation Shorthand way of showing electron configurations The number of electrons in a subshell are shown as a superscript after the subshell designation 1s 2s 2p 3s 3p 1s2 2s2 2p6 3s2 3p5

Writing Spectroscopic Notation 1 Determine the number of electrons to place 2 Follow Aufbau Principle for filling order Fill in subshells until they reach their max (s = 2, p = 6, d = 10, f = 14). 3 The total of all the superscripts is equal to the number of electrons. 4 Example: Write spectroscopic notation for S No charge written  Charge is 0 Atomic number for S = 16 = # of protons 0 = 16 - electrons 1s 2s 2p 3s 3p 2 2 6 2 4 Electrons = 16 2 + 2 + 6 + 2 + 4 = 16

Noble Gas Configuration

Noble Gases & Noble Gas Notation Noble Gas – Group 8 of the Periodic Table. They contain full valence shells. Noble Gas Notation – Noble gas is used to represent the core (inner) electrons and only the valence shell is shown. Br Spectroscopic 1s 2s 2p 3s 3p 2 6 4s 3d 10 4p 5 Noble gas [Ar] 4s 2 3d 10 4p 5 The “[Ar]” represents the core electrons and only the valence electrons are shown

Which Noble Gas Do You Choose? How do you know which noble gas to use to symbolize the core electrons? Think: Price is Right. How do you win on the Price is Right? By getting as close as possible without going over. Choose the noble gas that’s closest without going over! Noble Gas # of electrons He 2 Ne 10 Ar 18 Kr 36 Xe 54

Noble Gas Notation Example 1 Determine the number of electrons to place 2 Determine which noble gas to use Start where the noble gas left off and write spectroscopic notation for the valence electrons 3 Example: Write noble gas notation for As

Noble Gas Notation Example 1 Determine the number of electrons to place 2 Determine which noble gas to use Start where the noble gas left off and write spectroscopic notation for the valence electrons 3 No charge written  Charge is 0 Example: Write noble gas notation for As Atomic number for As = 33 = # of protons 0 = 33 - electrons [Ar] 4s 3d 4p 2 10 3 Electrons = 33 18 + 2 + 10 + 3 = 33 Closest noble gas: Ar (18) Ar is full up through 3p