An Electron s Address: Orbital Diagrams and Electron Configuration

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located in energy levels. The current model of the atom isn t as simple as that, however.

1 AP Chemistry Ms. Ye Name Date Block An Electron s Address: Orbital Diagrams and Electron Configuration Information: Energy Levels and Sublevels As you know, in his solar system model Bohr proposed that electrons are located in energy levels. The current model of the atom isn t as simple as that, however. Recall that the modern model of the atom (quantum model) pictures electrons moving around in regions called orbitals. Let s take a closer look at how energy levels and orbitals are related. Sublevels are located inside energy levels just like subdivisions are located inside cities. Each sublevel is given a name. Note the following table: TABLE 1 Energy Level Names of sublevels that exist in the energy level 1 st energy level s 2 nd energy level s and p 3 rd energy level s, p, and d 4 th energy level s, p, d, and f Note that there is no such thing as a d sublevel inside of the 2 nd energy level because there are only s and p sublevels inside of the 2 nd energy level. Questions: Use the information above to answer the following questions 1. How many/which sublevels exist in the 1 st energy level? 2. How many/which sublevels exist in the 2 nd energy level? 3. How many/which sublevels exist in the 3 rd energy level? 4. Does the 3f sublevel exist? (Note: the 3 stands for the 3 rd energy level.)

2 Information: Orbitals So far we have learned that inside energy levels there are different sublevels. Now we will look at orbitals. Orbitals are located inside sublevels just like streets are located inside subdivisions. Different sublevels have different numbers of orbitals. TABLE 2 Sublevel # of Orbitals Possible s 1 p 3 d 5 f 7 Here s an important fact: only two electrons can fit in each orbital. So, in an s orbital you can have a maximum of 2 electrons; in a d orbital you can have a maximum of 2 electrons; in any orbital there can only be two electrons. Since a d sublevel has 5 orbitals (and each orbital can contain up to two electrons) then a d sublevel can contain 10 electrons (= 5 x 2). Pay attention to the difference between sublevel and orbital. 5. Use the information from table 1 and table 2 to determine the total number electrons that can fit in each energy level. The 2 nd energy level has been done for you as an example. Energy Level Types of Sublevels # orbitals x # electrons in each orbital Total # of Electrons in this Energy Level 1 st energy level 2 nd energy level s and p s: 1 x 2 = 2 p: 3 x 2 = 6 3 rd energy level 8 4 th energy level

3 Information: Representing the Most Probable Location of an Electron The following is an address for an electron a sort of shorthand notation. The diagram below represents an electron located in an orbital inside of the p sublevel in the 3 rd energy level. EXAMPLE #1: Some important facts about the above diagram: The arrow represents an electron. The upward direction means that the electron is spinning clockwise. 3p means that the electron is in the p sublevel of the 3 rd energy level. Each blank represents an orbital. Since there are three orbitals in a p sublevel, there are also three blanks written beside the p. In the diagram, the electron is in the first of the three p orbitals. Here s another example: EXAMPLE #2: Questions: Use the information above to answer the following questions 6. In example #2, why are there 5 lines drawn next to the d? 7. In example #2, what does it mean to have the arrow pointing down? 8. Write the notation for an electron in a 2s orbital spinning clockwise. 9. Write the notation for an electron in the first energy level spinning clockwise. Now let s look at how to represent the location of all the electrons of an atom of a specific element.

4 Orbital Diagrams In the following examples, you will look at how electrons are filled in the various orbitals. Some drawings show correct electron configurations and some show incorrect electron configurations. You will use these drawings to figure out the rules for electron configuration PART I: What is the rule for the number of electrons and the direction of the arrow in ONE orbital? Note: an arrow represents one electron. Each small box represents one orbital 1. What does each arrow represent in the orbital diagrams above? 2. What do the 3 boxes next to the 2p sublevel represent? 3. Pauli Exclusion Principle (1): What is the maximum number of electrons allowed in each orbital? How is this represented in the correct orbital diagram? 4. Pauli Exclusion Principle (2): If two electrons occupy the same orbital, they must have. Circle the correct answer. a. the same spin b. opposite spins 5. What element do you think the correct orbital diagram pictured is representing (assume the atom is neutral)? How do you know?

5 PART II: What is the rule for how electrons fill multiple orbitals? Aufbau Principle: Examine the order of how electrons fill up the orbitals. Circle the correct responses to the questions below. 1. Based on where a single electron is placed, the lowest energy electron in an atom is found in the sublevel. a. 1s b. 2s c. 3s 2. Electrons will occupy a p-orbital only after a. the previous s-orbital is completely full b. the previous s-orbital is empty 3. Electrons can begin to occupy energy levels with the next highest integer designation (e.g. 2 vs. 1, 3 vs. 2) only after on the energy levels below it are completely occupied. a. at least one of the orbitals b. all of the orbitals Hund s Rule: Compare the correct and incorrect electron configurations for nitrogen and oxygen and focus on the 2p orbitals. Circle the correct responses to the questions below. 1. Electrons will pair up in an orbital only when a. there is an even number of electrons in the sublevel b. all orbitals in the same sublevel already have one electron 2. When single electrons occupy different orbitals of the same sublevel,. a. they all have the same spin b. they all have different spins

6 Orbital Diagram Rules: There are three rules that govern the arrangement of electrons in an atom s orbitals: 1. The Aufbau Principle: Under normal condition, each electron occupies the lowest energy levels possible 2. The Pauli Exclusion Principle: a maximum of 2 electrons can occupy an orbital space, but only if they have opposite spins 3. Hund s Rule: to minimize repulsion between electrons, we put one electron in each orbital of the same energy level before we add the second electron. Practice: Based on the rules you looked at, complete the ground state orbital diagrams and write the corresponding electron configurations for the following elements: Beryllium Sodium Carbon Boron Phosphorus Chlorine

7 Electron Configurations are the written address of the electrons. There are 3 parts to the electron configuration: The Periodic Table gives you information regarding which orbitals are being filled: **Note: The electron configuration for Helium is 1s 2 Determining the Electron Configuration Using the Periodic Table 1. Determine the # of electrons in your atom 2. Go row by row and block by block on the Periodic Table until you reach the element or the # of electrons desired. Ex 1: Beryllium Be: atomic number = 4. A neutral Be atom has 4 electrons. The entire 1s block must be filled, so Be has 2 electrons in the 1s orbital. The entire 2s block must be filled, so Be also has 2 electrons in the 2s orbital. The full electron configuration for Be would be written as 1s 2 2s 2 The subscripts (2 and 2) add up to 4, which is the total number of electrons. Ex 2: Oxygen O: atomic number = 8. A neutral O atom has 8 electrons. The entire 1s block must be filled, so O has 2 electrons in the 1s orbital. The entire 2s block must be filled, so O also has 2 electrons in the 2s orbital. To get to Oxygen, 4 electrons must be filled in the 2p orbital. The full electron configuration for O would be written as 1s 2 2s 2 2p 4 The subscripts (2, 2, and 4) add up to 8, which is the total number of electrons.

8 Writing Electron Configurations: Element # of e - Long Form Electron Configuration Noble Gas Abbreviation # valence e - s Be 4 1s 2 2s 2 (see example) [He] 2s 2 2 O 8 1s 2 2s 2 2p 4 (see example) [He] 2s 2 2p 4 6 Na S K Al Cl Fe Ca Br Cu A shortened form of the electron configuration can be written for most elements. The shortened form is often referred to as the Noble Gas abbreviated electron configuration, or the short form. Valence Electrons Electrons in the outermost energy level The # of valence electrons = the total # electrons in the highest s & p sublevels (must be of the same energy level)

An Electron s Address

Honors Chemistry Name Date Block An Electron s Address Information: Energy Levels and Sublevels As you know, in his solar system model Bohr proposed that electrons are located in energy levels. The current