Electron Orbitals and Electron Configurations Part II (a)

From orbits to orbitals! We are going to move from Bohr’s model into the Quantum model of the atom We are moving closer to our current understanding of where electrons are located in the atom

3 Electron Cloud or Orbitals Erwin Schrödinger used mathematics to predict probability of finding an electron at a certain location in the atom He call the area of probability the electron cloud = the volume around the nucleus of an atom where its electrons are most likely found ––I––I

Electron Cloud or Orbitals We can’t be absolutely certain where any electron is at any time – –But based on what science knows presently, this is our very best guess Orbital = a region with a very high probability of finding the electron when it has a particular amount of energy

Electron Cloud or Orbitals Think of the energy levels as the rungs on the ladder of the electron cloud Just like we can only stand on the rungs of a ladder and not between the rungs, the electron can be located only in certain energy levels within the atom – –Lower energy levels are smaller and located closer to the nucleus of the atom – –Higher energy levels are larger and located farther away from the nucleus

6 The Quantum-Mechanical Model Each energy level (or shell) contain the same number of subshells or sublevels as the energy level The subshells are represented as a letter –s, p, d, f Each subshell has orbitals with a particular shape.

7 Shells & Subshells

8 The Quantum- Mechanical Model Energy Level# of subshellsOrbital shape 11s 22s and p 33s, p, and d

Apartment Complex Analogy Think of an atom like an apartment complex The energy level or shell is the floor The subshells are the type of apartment – –s = suited = deluxe – –p = penthousef = flat The orbitals have different occupancies based on their shape

10 Probability Maps & Orbital Shape s orbitals are spherical and have 1 orbital

11 Probability Maps & Orbital Shape p orbitals look like dumb bells and have 3 orbitals

Probability Maps & Orbital Shape d orbitals have 5 orbitals

Probability Maps & Orbital Shape Probability Maps & Orbital Shape f Orbitals have 7 orbitals 13

Atomic Orbitals Watch the video (14:28) RlVNBSA Stop and answer questions about Atomic Orbitals

Electron Orbital Activity Lab There are funny rules on how to fill the apartment complex or atom Work with a partner to complete the electron configuration lab, but be sure to follow these rules…

Apartment Rules Rule A: 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.

Apartment Rules Rule B: 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.

Apartment Rules Rule C: 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 an arbitrary rule on the part of the owners: in a just world we wouldn’t have to follow it. But quantum mechanics has nothing to do with justice.

Ions Ions are atoms that have either lost or gained electrons Remember electrons are negative, so how many protons and how many electrons would Cl -1 have?

Electron Lab Now work with a partner to complete the Electron Orbital Activity Lab

What did we learn from the Lab? Bohr part II (b)

Rule A: The Aufbau Principle Place electrons in the energy shells and orbitals in order of energy, from low energy to higher energy – –i.e. Electrons are Lazy! – –s → p → d → f All orbitals related to an energy level are of equal energy. – –i.e. The three 2p orbitals are the same energy level.

Rule B: Hund’s Rule When filling orbitals that have the same energy, place one electron in each before completing pairs – –i.e. Electrons are unfriendly! Why? Electrons, being unfriendly, fill up the empty orbitals before sharing orbitals. This is similar to seats on a bus – on a bus, you sit alone, rather than with a stranger, if there is an option.

Rule C: Pauli Exclusion Principle A maximum of two electrons may occupy a single orbital, but only if the electrons have opposite spins. – –Spin -- Electrons have an associated “spin,” either one way or the other, like a top. – –These spins are called “spin up” and “spin down.”

Big take aways from the Lab Exceptions to filling order are copper, chromium and some others Most stable are completely filled shells Next most stable are half-filled shells An atom may borrow an electron from next s shell to half fill a lower energy level.

Take aways from the Lab Did you notice something funny about the order of the energy levels or orbitals? Energy levels don’t always go in order!

Relative Energy Levels

Take aways from the Lab Occupanies: Did you notice how many electrons could occupy each type of room? Suites (s orbitals) could hold 2 Penthouse (p orbitals) could hold 6 Deluxe (d orbitals) could hold 10 Flats (f orbitals) could hold 14

Orbital Occupancies Subshell NameNumber of Orbitals Max number of electrons s- subshell1 (sphere)1 X 2 = 2 p – subshells3 (dumbbells)3 x 2 = 6 d – subshells55 x 2 = 10 f – subshells77 x 2 = 14

30 Writing electron configurations Writing electron configurations Electron configuration = distribution of electrons into the various energy shells and subshells in an atom in its ground state

Electron Configurations Electron configuration is address information for electrons The most stable arrangement is called the ground-state electron configuration. This is the configuration where all of the electrons in an atom reside in the lowest energy levels possible.

Electron Configurations 2p 4 Energy Level Subshell Number of electrons in the subshell 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.

Tro's Introductory Chemistry, Chapter 9 33 Electron Configurations Nitrogen: 1s 2 2s 2 2p 3 (atomic number = 7) energy level orbital how many electrons in that orbital

What about ions? What did you notice about ions? When writing electron configuration for ions (when an element loses or gains electrons to become more stable), do it exactly the same way for the ion’s number of electrons

Writing Electron Configurations Wouldn’t it be nice if we could write electron configuration without doing the orbital diagrams? Well, we can! But we need to be careful because the energy levels do not always go in order! We can use the diagonal rule to help us!

Diagonal Rules s 3p 3d s 2p s 4p 4d 4f s 5p 5d 5f 5g? s 6p 6d 6f 6g? 6h? s 7p 7d 7f 7g? 7h? 7i? By this point, we are past the current periodic table so we can stop.

Writing Electron Configurations Steps for the diagonal rule: Write the energy levels top to bottom. Write the orbitals in s, p, d, f order. Write the same number of orbitals as the energy level. Draw diagonal lines from the top right to the bottom left. To get the correct order, follow the arrows!

Diagonal Rule Now try it yourself on the blank side of the diagonal rule sheet Doing this will be #1 on your next quiz!

Practice Using the Diagonal Rule Work on writing the electron configurations for the 10 elements in the packet