Electron Configuration How electrons are arranged Or Goodbye Bohr!

Quantum Mechanics quantum mechanics In quantum mechanics, orbitals the electrons occupy specific energy levels (as in Bohr's model) but they also exist within specific probability volumes called orbitals with specific orientations in space. The electrons within each orbital has a distinct spin.

Probability Under this new model, we cannot predict exactly where an electron is. Rather we can say that electrons are most likely found within certain areas. These are called probability volumes (note the volume: 3D)

n n = The principle quantum number Describes the possible energy levels (how close it is to the nucleus) and pictorially it describes the orbital size. n = 1, 2, 3…. where an orbital with the value of 2 is larger than an orbital with the value of 1. 2s 3s 1s

Quantum Mechanics l l = angular momentum quantum number Describes the "shape" of the orbital and can have values from 0 to n - 1 for each n. orbital designation :s p d f

Quantum Mechanics m l = magnetic quantum number l ll Related to the orientation of an orbital in space relative to the other orbitals with the same l quantum numbers. It can have values between l and - l. So for s, only 1 orientation is possible But for p, s orientations are possible How many are possible for d? f?

Quantum Mechanics m s = spin quantum number An electron has either + 1 / 2 or - 1 / 2 spin values; sometimes referred to as spin up and spin down. These are arbitrary and are only used to designate different “addresses” for the electrons

What does the electron cloud look like? NOT THIS!!!

More like this: 1S 2S 2P x 2p y 2P z 3S Each orbital contains 2 electrons maximum, with opposite spins

House/Inn/Apartment Model

Rooms: the “s” One room, one bed Can sleep one or two If two, must sleep head to toe

Rooms: the “p” Three rooms One bed per room One or two per bed NO ONE shares until all rooms have an occupant If two, must sleep head to toe

Rooms: the “d” LUXURY!! Five rooms, one bed per room, up to two per bed NO ONE can double up until all rooms are occupied

House Model 1s 2s 3s 4s 5s 2p 2p 2p 3p 3p 3p 4p 4p 4p 5p 5p 5p 6p 6p 6p6s 3d 3d 3d 3d 3d 4d 4d 4d 4d 4d 5d 5d 5d 5d 5d 36 6d 6d 6d 6d

Electron Configuration Examples: H: He: Li : Co: Br: red is valence electrons why aren’t d valence? 1s 1 1s 2 1s 2 2s 1 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 7 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5

1s2s3s4s5s6s 2p3p4p5p6p3d4d5d6d4f5f6f5g6g 7s 7p7d 8s 8p7f8d 9s 9p 10s 1s 2s 3s 4s 5s 6s 7s 8s 9s 10s 2p 3p 4p 5p 6p 7p 8p 9p 3d 4d 5d 6d 7d 8d 9d 4f 5f 6f 7f 8f 9f 5g 6g 7g 8g 9g 6h 7h 8h 9h 10p10d10f10g10h But check out this simple table at right. If you draw diagonal arrows starting at the bottom like this… It shows the precise order in which the energy levels are arranged from lowest to highest! +

s p d f He H So what does all this have to do with chemistry? Below is a rough sketch of the periodic table. For the sake of this discussion, we are going to move He over so it is in that little open space next to H: And now we are going to number the periods 1 through 7: As you will see, these periods correspond (more or less) to the energy levels we’ve just been discussing. And we are going to designate the four distinct rectangular blocks by the type of sublevel they match up with: “s,” “p,” “d” and “f:” Now let’s take the first ten sublevels (1s, 2s, 2p…) and see how the electrons filling these sublevels takes us row by row across the periodic table, and allows us to read electron configurations right off the table… And let’s also number the groups within each block (1,2,3,4…)

1s 2s 3s 4s 2p 3p 4p 3d 4d s p d f OK, so we’re going to use arrows pointing up or down to represent the electrons. Can you guess into which box the first electron would go given that it is attracted to the nucleus? s +

1s 2s 3s 4s 2p 3p 4p 3d 4d s p d f 1s That’s right: it goes in the 1s sublevel. And its el. config is 1s 2. Notice in the table above where H is – in the area designated as 1s. So where does the next electron go? s +

1s 2s 3s 4s 2p 3p 4p 3d 4d s p d f 1s s If you were thinking it went in the 2s, then you forgot that each orbital can hold up to two electrons. Note how He is right here in the area designated as 1s 2 and so its el. config. is 1s 2. +

1s 2s 3s 4s 2p 3p 4p 3d 4d s p d f 1s 2 2s s Now that the 1s is filled, the next electron goes in the next sublevel – the 2s. Again note how Li is in 2s 1. Its full el. conf. is 1s 2 2s 1. What is Be’s el. conf? +

1s 2s 3s 4s 2p 3p 4p 3d 4d s p d f 1s 2 2s s Now that the 1s is filled, the next electron goes in the next sublevel – the 2s. Again note how Li is in 2s 1. Its full el. conf. is 1s 2 2s 1. What is Be’s el. conf? +

1s 2s 3s 4s 2p 3p 4p 3d 4d s p d f 1s 2 2s 2 2p s Is this what you were thinking? Notice how B is in the 2p 1 spot. So its full el. conf. is 1s 2 2s 2 2p 1. What’s next? +

1s 2s 3s 4s 2p 3p 4p 3d 4d s p d f 1s 2 2s 2 2p s Is this what you were thinking? Notice how C is in the 2p 2 spot. So its el. conf. is 1s 2 2s 2 2p 2 Notice also how when we fill a sublevel… +

1s 2s 3s 4s 2p 3p 4p 3d 4d s p d f 1s 2 2s 2 2p s …we put one electron in each orbital until the sublevel is half filled… +

1s 2s 3s 4s 2p 3p 4p 3d 4d s p d f 1s 2 2s 2 2p s … and then we go back and start pairing off This is called “Hund’s Rule, but it also referred to as the bus seat rule. Can you figure out why? +

1s 2s 3s 4s 2p 3p 4p 3d 4d s p d f 1s 2 2s 2 2p s Look at F. It’s just one electron away from having filled 2p sublevel… And it’s just one square away from the end of the 2p block. +

1s 2s 3s 4s 2p 3p 4p 3d 4d s p d f 1s 2 2s 2 2p s And then Ne has a completely filled outer level. Na is next. Can you guess where the next electron is going to go? +

1s 2 2s 2 3s 2 2p 6 3p For example, Cl (#17) which is right here on the table: So the answer would be 1s 2 2s 2 2p 6 3s 2 3p 5 The short cut would be: [Ne]3s 2 3p 5

Orbital Diagrams Orbital diagrams are written in order of increasing energy levels starting with the lowest energy level the 1s orbital. ___ ___ ___ 4p ___ ___ ___ ___ ___ 3d ___ 4s ___ ___ ___ 3p ___ 3s ___ ___ ___ 2p ___ 2s ___ 1s RULES: (1) fill the lowest energy level first (2) fill each orbital in a subshell with one electron first before you double up. (3) Completely fill each subshell before proceeding to the next energy level. Remember the order!!

Orbital Diagrams Practice Problems 1. Fill in the orbital diagrams for: C ONe Na Si Cl Ar K ___ ___ ___ 4p __ __ __ __ __ 3d ___ 4s ___ ___ ___ 3p ___ 3s ___ ___ ___ 2p___ 2s___ 1s

Orbital Diagrams Practice Problem Answers Fill in the orbital diagrams for: C O ___ ___ ___ 4p __ __ __ __ __ 3d ___ 4s ___ ___ ___ 3p ___ 3s ___ ___ ___ 2p___ 2s___ 1s

Orbital Diagrams Practice Problem Answers Fill in the orbital diagrams for: Ne Na ___ ___ ___ 4p __ __ __ __ __ 3d ___ 4s ___ ___ ___ 3p ___ 3s ___ ___ ___ 2p___ 2s___ 1s

Orbital Diagrams Practice Problem Answers Fill in the orbital diagrams for: Si Cl Si Cl___ ___ ___ 4p __ __ __ __ __ 3d ___ 4s ___ ___ ___ 3p ___ 3s ___ ___ ___ 2p___ 2s___ 1s

Electron Configuration Electron configuration is a shorthand notation for describing the arrangement of the electrons about the nucleus. General Format using the quantum numbers: n l e- n l e- RULES: 1. Fill the lowest energy levels first. 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p 2. No more than two electrons per orbital. 3. Ready for an easier way? n = principle quantum number l = angular momentum quantum number e- = number of electrons Lowest

Examples of the condensed configuration: 3d 7 Li:[He] 2s 1 Co:[Ar] 4s 2 3d 7 3d 10 4p 5 Br:[Ar] 4s 2 3d 10 4p 5 The condensed electron configuration distinguishes the core electrons from the valence electrons. CORE CORE electrons are tightly held to the nucleus and resemble a noble gas configuration. VALENCE VALENCE electrons are the outer most electrons and are involved in chemical reactions.