Honors Chemistry Unit Three Quantum Theory

The Rules – Page 7 & Notesheet 1. The Aufbau Principle Would you rather drive 10 min. to a restaurant or 1 hour to the exact same restaurant? Same with electrons Aufbau 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 Sublevel SublevelNumber ofMaximum (suite) Orbitals # of e- s12 p36 d510 f714

Electrons in Each Energy Level – Back to the Notesheet Energy Level Sublevel(s) Present # of Orbitals # of Electrons 1s1 2 2s, p1 + 3 = 4 8 3s, p, d = 918 4s, p, d, f = 16 32

Orbital Notation Shows all 4 quantum numbers of individual electrons. Start by drawing out Energy Level SubLevel Orbital

Let’s Look at Nitrogen Atomic # = 7, so 7 electrons Start in order n = 1, just the s sublevel and 1 orbital n = 2, s and p sublevels, 1 and 3 orbitals Fill each sublevel before moving onto the next sublevel 1s 2s 2p

Let’s Look at Nitrogen Atomic # = 7, so 7 electrons Fill each sublevel before moving onto the next sublevel 2 electrons in 1s 2 electrons in 2s 3 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 Example An atom of carbon has 6 electrons arranged in the following order. 1s 2 2s 2 2p 2 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. 1s 2 2s 2 2p 6 3s 1 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-. ( )

An atom of gold has 79 electrons arranged in the following order. 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 5d 9 Superscripts must add up to the atomic number of the element. (#p+ = #e-) Gold has 79 p+ and 79 e-. ( ) How About a Tougher One???

Electron Configuration Short 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 platinum How many electrons does it have? If we used orbital notation we would have to draw 78 arrows If we used electron configuration notation we’d have to write 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 5d 8 THIS TAKES FOREVER!

Noble Gas Configuration – Short Cut Calcium Atomic Number 20 Electron Configuration Long Form 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Electron Configuration Short Form [Ar]4s 2

Thank you, may I have another??? Tin Atomic Number 50 Electron Configuration Long Form 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 2 Electron Configuration Short Form [Kr]5s 2 4d 10 5p 2

So, what if it is a noble gas? Neon Atomic Number 10 Electron Configuration Long Form 1s 2 2s 2 2p 6 Electron Configuration Short Form [He] 2s 2 2p 6

Lewis Dot Structures One 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 B B = Kernel (The protons, neutrons and full electron shells.) Valence shell electrons

You can use the Electron Configuration to get the Lewis Dot Structure… Ca 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 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]4s 2 Ca

One Final Example Tin 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 2 Or [Kr]5s 2 4d 10 5p 2 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.

Ne So, it goes like this…