Honors Chemistry Unit Three

Quantum Theory

The Rules – Page 7 & Notesheet1. The Aufbau Principle

Would you rather drive 10 min. to a restaurant or 1 hour to the exact same restaurant?Same with electronsAufbau Principle - Electrons enter orbitals of lowest energy level first.

Filling Order

• The image below tells us the order of how electrons fill orbitals.

• It goes by energy level and sublevel.• We can also read this by looking at the Periodic

Table.

Filling Order – Follow Atomic #

The order:1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p

6s 5d 4f 5d 6p 7s 6d 5f 6d 7p

2. Pauli Exclusion Principle – Page 7

Pauli Exclusion Principle – An orbital can hold a maximum of 2 electrons. To occupy the same orbital, the 2 electrons must spin in opposite directions.

3. Hund’s Rule – Page 7

Hund’s Rule - one electron enters each orbital until each orbital contain one electron with parallel spins before a second electron is added.Electrons like to stay hund paired for as long as possible

Number of Electrons per SublevelSublevel Number of

Maximum (suite) Orbitals # of e-s 1 2

p 3 6d 5 10f 7 14

Electrons in Each Energy Level – Back to the Notesheet

Energy Level Sublevel(s) Present

# of Orbitals # of Electrons

1 s 1 2

2 s, p 1 + 3 = 4 8

3 s, p, d 1 + 3 + 5 = 9 18

4 s, p, d, f 1 + 3 + 5 + 7 = 16

32

Orbital NotationShows all 4 quantum numbers of individual electrons.Start by drawing out

Energy LevelSubLevelOrbital

Let’s Look at Nitrogen

Atomic # = 7, so 7 electronsStart in order

n = 1, just the s sublevel and 1 orbitaln = 2, s and p sublevels, 1 and 3 orbitalsFill each sublevel before moving onto the next sublevel

1s 2s 2p

Let’s Look at Nitrogen

Atomic # = 7, so 7 electronsFill each sublevel before moving onto the next sublevel2 electrons in 1s2 electrons in 2s3 electrons in 2p (Use Hund’s Rule!)

1s 2s 2p

Orbital Notation

1s 2s 2p

1s 2s 2p 3s

Carbon

Sodium

Electron Configurations

Show the arrangement of electrons in an atom.Describes the first 2 quantum numbers for each electron.

Energy level and sublevel.Usually represent the ground state of the electrons.

Let’s Try an ExampleAn atom of carbon has 6 electrons arranged in the following order.

1s22s22p2

It has 4 electrons in its highest level.Superscripts must add up to the atomic number of the element. (#p+ = #e-) Carbon has 6 p+ and 6 e-. (2+2+2)

How about another one???An atom of sodium has 11 electrons arranged in the following order.1s22s22p63s1

Sodium’s electrons require three energy levels. (Third quantum number.)It has 1 electron in its highest level.Superscripts must add up to the atomic number of the element. (#p+ = #e-)Sodium has 11 p+ and 11 e-. (2+2+6+1)

An atom of gold has 79 electrons arranged in the following order.

1s22s22p63s23p64s23d104p65s24d105p66s24f145d9

Superscripts must add up to the atomic number of the element. (#p+ = #e-)

Gold has 79 p+ and 79 e-. (2+2+6+2+6+2+10+6+2+10+6+2+14+9)

How About a Tougher One???

Electron ConfigurationShort Form

Notice that large portions of each electron configuration is repetitive.To write an electron configuration in short form:

1. Find the element on the periodic table and “back up” to the previous noble gas.

2. Write the symbol for the noble gas in brackets, then continue with the remainder of the electron configuration.

Noble Gas Configuration

Lets looks at platinumHow many electrons does it have?If we used orbital notation we would have to draw 78 arrowsIf we used electron configuration notation we’d have to write1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d8

THIS TAKES FOREVER!

Noble Gas Configuration – Short Cut

CalciumAtomic Number 20

Electron Configuration Long Form1s22s22p63s23p64s2

Electron Configuration Short Form[Ar]4s2

Thank you, may I have another???

TinAtomic Number 50

Electron Configuration Long Form1s22s22p63s23p64s23d104p65s24d105p2

Electron Configuration Short Form[Kr]5s24d105p2

So, what if it is a noble gas?Neon

Atomic Number 10

Electron Configuration Long Form1s22s22p6

Electron Configuration Short Form[He] 2s22p6

Lewis Dot StructuresOne more type of atomic model…

(In addition to Bohr models and long and short electron configurations)

Consists of the element’s symbol and the atom’s valence electrons.Symbol = kernel (represents the protons, neutrons and full electron shells).Dots = valence electrons.

Lewis Dot Structures Con’t

BB = Kernel (The protons, neutrons and full electron shells.)

Valence shell electrons

You can use the Electron Configuration to get the Lewis Dot Structure…

Ca1s22s22p63s23p64s2

Locate the highest quantum number. (4)Add the s and p orbital electrons, and place

them around the element symbol. (2)Look how easy this is with the short form.

[Ar]4s2

Ca

One Final ExampleTin

1s22s22p63s23p64s23d104p65s24d105p2

Or[Kr]5s24d105p2

Locate the highest quantum number (5)Add the s and p orbital electrons (4)

Sn

How to place electrons on a Lewis Dot

First two dots represent the s orbital electrons and are placed at the top of the element’s symbol.Then the p orbital electrons are placed in this order: right, bottom, left, right, bottom, left.

Ne1 2

3

45 6

7

8

So, it goes like this…