Orbitals What you need to know: Some things to keep in mind: What order to fill the orbitals as you get more electrons Even easier than figuring the number of electrons per energy level We’ll do that after going over the shapes and locations of the orbitals - Octet Rule Some things to keep in mind: You don’t have to know the shapes, so don’t freak out about them You don’t really need to know this for most things you would do as a chemist, though it will help. Something neat to be familiar with as it helps to visualize what we mean when we talk about valence electrons in a later chapter. It also helps make sense as to what it means by having 4 orbitals in energy level 2. Observe that they are trying to get as close to the positively charged nucleus as possible (opposite charges attract) while at the same time are trying to avoid each other as much as possible (similar charges repel). What we will be doing today.

(& Similar charges repel) Orbitals Electrostatic Force – the force that keeps electrons attracted to the nucleus – the opposite charges attract each other Electrons have a negative charge Protons have a positive charge OPPOSITES ATTRACT (& Similar charges repel)

Orbitals This is basically a packing problem … electrons want to get as close as possible to the nucleus (opposites charges attract each other) while staying as far away from each other as possible (similar charges repel each other). At some point, the repulsion of the similar charges of electrons won’t allow any more in the space of that orbital Very, very simplistic explanation

1st Energy Level Energy level 1 has: 1 orbital Maximum of 2 electrons

Orbitals 1s Energy level 1 has one orbital The 1s orbital 1 stands for energy level S stands for the shape 1s1 means there’s 1 electron 1s2 means there are 2 electrons Is a sphere – can visualize as a ball.

2nd Energy Level Energy level 2 has: 4 orbitals Maximum of 8 electrons One s orbital Three p orbitals Maximum of 8 electrons

Orbitals 2s One orbital is the 2s orbital Energy level is 2 S stands for the shape Again spherical, but now a little bigger and enclosing the S1 He in this picture means the 1s orbital that we find in He Like a ball within a ball.

Orbitals 2p Energy level 2 has 4 orbitals The 2S orbital (one) The 2p orbitals (three) (jacks) Are 3 p orbitals p orbitals are oriente on the x, y, z axes (length, width, height) <<< hmmm … they overlap with the S orbitals but still extend beyond them … thus available to interact with other electrons! Like a jack in the game Jacks – where you have a ball and jacks. First, note that this configuration allows the electrons to be as far apart from each other while they are as close the nucleus as possible. The second BIG thing is, note that just the tips of the p orbitals stick out of the s orbital. This means there are up to (but no more than) 8 electrons on the “outside” of the electron cloud / atom.

3rd Energy Level Energy level 3 has: 9 orbitals One s orbital Three p orbitals Five d orbitals Maximum of 18 electrons

Orbitals 3s One 3s orbital An even bigger S orbital enclosing the 1s, 2s, 2p orbitals

Orbitals 3p Energy level 3 has three p orbitals The 3S orbital (one orbital) The 3p orbitals (three orbitals) Notice again, the p orbitals have just the tips outside the s orbital, allowing for up to, but no more than 8 electrons on the “surface” of the atom.

Orbitals 3d Energy level 3 has five d orbitals The 3s orbital (one orbital, 2 electrons) The 3p orbitals (three orbitals, 6 electrons) The 3d orbitals (five orbitals, 10 electrons) These are interspersed around the p orbitals So, I don’t have a drawing of these orbitals in relation to the others, but please note the IMPORTANT fact that they are all within the s orbital. Thus even though there are even more electrons than before, there are still only up to 8 electrons on the “surface” of the atom. This will be VERY important to us soon!

Electron Configuration Another way of showing where the electrons are located. Ex: Helium = 1s2 1 = energy level S = type of orbital 2 = number of electrons Ex: Lithium = 1s22s1 1 & 2 = energy levels 2 & 1 = number of electrons

Orbital Energy Levels Orbitals can have different energy levels too Note that the 4s orbital is a lower energy level than the 3d. Since electrons want to fill the lowest energy orbital they can first, the 4s will be filled before the 3d. Thanks to our hero Aufbau, knowing which orbitals to fill first is easy to remember! Orbitals have different energy levels WITHIN the energy level they occupy. Electrons ALWAYS fill the lowest energy levels first! (This is called the Aufbau Rule. Aufbau is the German word for “order”, or the order that orbitals are filled in.) Just like water always fills the bottom of a glass first, never from the top down. Therefore, since the 4s orbital is lower than the 3d orbitals, it will be filled first even though it is technically in a higher energy level. All this means is that it takes less energy to fill the 4s orbital than trying to stuff even more electrons within the 3rd energy level. Think of it like packing for a trip – at some point it becomes easier to just pack a second suitcase than try and stuff all your clothes into the one.

Aufbau Chart Energy Level Nucleus Energy level 1 has 1 type of orbital (s) Energy level 2 has 2 types of orbitals (s & p) Energy level 3 has 3 types of orbitals (s & p & d) The Aufbau (“order”) chart. This is an easy way to remember which orbitals are filled in first. Note on each energy level that the order of orbitals is spdf. Note too, that each energy level has as many orbitals as the energy level, up to a max of “f”. (While theoretically it can be more, there are no atoms large enough for a “g” orbital, so up through “f” is all the further you need to go.) Also note that the chart is NOT read left to right, but at a diagonal. When you reach the end of the orbitals in the diagonal, you go to the next diagonal arrow and follow it. This is a much easier way than memorizing the order to fill orbitals! Everyone needs to be able to read it & Pre-AP needs to be able to draw this chart. Note that it only goes to 7p. This accounts for all 7 energy levels we have discovered to date. It also corresponds to the 7 rows of the periodic table! Just remember – if you forget this, it’s a speedy F (spdf).

Electron Configurations The maximimum number of electrons for each orbital are: s = 2 p = 6 d = 10 f = 14 note that each orbital holds 4 more than the previous! Just listing the electrons in order of how they are filled for each atom / element Just follow the aufbau chart along the diagonal lines

Electron Configurations The electron configuration for H is: 1s1 or, the electron is in the 1st energy level, s-orbital, and there is 1 electron For Lithium, it is: 1s2 2s1 or, the electrons are located (in order filled) in the 1st energy level, s-orbital, and there are 2 of electrons, and the 2nd energy level, in the s-orbital, has 1 electron. Just follow the aufbau chart along the diagonal lines

Orbitals through 4s

All the shapes of the orbitals

Group Work Aufbau Chart (just do one) & electron configurations for H through Ne

Exit Ticket Aufbau Chart (just do one) & electron configurations for Li and C

Bell Work Day 2 Electron Config

Group Work 1 Day 2 Electron Config

Exit Ticket & HW Day 2 Electron Config

Quiz

Valence Electrons The outer shell of electrons are called the valence electrons These are important because it’s the outer electrons that interact with each other (form bonds between atoms) There will never be more than 8 valence electrons Because we fill the d orbital is “buried” under the s & p orbitals, these (s & p orbitals) are always on the outer shell (2 + 6 = 8)

Electron Dot Structures As Chemists we are primarily concerned with the valence electrons Electron Dot Structures give us an easy, quick way of visualizing the valence electrons For now just need to know the electron dot structures for H through Ne

Dot Structure for Hydrogen

Dot Structure for Helium

Dot Structure for Lithium

Dot Structure for Beryllium

Dot Structure for Oxygen

Dot Structure for Fluorine

Calculating Average Atomic Mass Convert the percentages into decimals. (This percentage is known as its relative abundance or percent abundance) Multiply the percentage of each isotope by its respective mass. Add the numbers from step two together.

Calculating Average Atomic Mass Example: Isotopes At. Mass Abundance 24Mg 23.9850 78.99% 25Mg 24.9858 10.00% 26Mg 25.9826 11.01% (23.9850 x 0.7899) + (24.9858 x 0.1000) + (25.9826 x 0.1101) = 18.9458 + 2.4986 + 2.8607 = 24.3051

Group Work

Octet Rule (An introduction) Octet Rule: The outer shell of an atom always wants to be full (or in the case of H empty). The prefix octo- means 8 Atoms want to be neutral, but also want their outer shell of electrons to be full They want to be like the Noble Gases

Octet Rule The S orbital (2 electrons) is the outer layer for H & He H only has 1 valence electron He only has 2 valence electrons

Octet Rule The p orbital can hold 6 electrons With the s orbital’s 2 electrons this equals 8 These 8 electrons (or lack thereof) primarily determine the interactions of all the elements

Octet Rule 8 is the “magic” number! So … except for the first period of elements (H & He) … 8 is the “magic” number!

Octet Rule The first shell (energy level) only needs 2 electrons to be full After that, all the shells need 8 electrons to be full Therefore: If there are less than 4 electrons, the atoms will want to give them away to other elements If there are more than 4 electrons, the atoms will want to take them from other elements

Octet Rule Just remember: The number of electrons to fill the first shell is 2 The number of electrons to fill all the other shells is 8

Octet Rule If you forget, Look at the period (row) the element is in That will tell you the number of shells Look at the group / family (column) the element is in That will tell you the number of valence electrons

Worksheets Draw Bohr models for K - Kr

The End

Spherical Radii of the Orbitals

Aufbau Chart Chemistry Physics Energy Level Energy Level Nucleus A Chemist views energy levels based on how they are filled in real life, as well as how they will interact with other atoms. An energy level is filled when the outer electrons (valence electrons) equal 2 (as in He), or 8 (as in Ne & Ar). This is much more practical and a better predictor of how the atoms will interact with each other. 2 e- 8 e- 18 e- 1 2 3 4 The easiest way to remember the number of electrons to fill an energy level in Chemistry is to count the number of boxes in a period (horizontal line) on the periodic table.

Group Work Can we make the Principles come out? Table