Understanding Orbital Diagrams and Electron Configurations

1. Chapter 5 Electronic Structure and Periodic Trends 5.4 Orbital Diagrams and Electron Configurations Learning Goal Draw the orbitaldiagram and write the electronconfiguration for an element.

2. Orbital Diagrams Orbital diagrams • explain how electrons are arranged withinthe atom • show the order in which electrons are placedin orbitals • use boxes to represent orbitals • use colors to represent sublevels s, p, d, f

3. Orbital Diagram

4. Electrons in Orbital Diagrams To place electrons in orbital diagrams, electrons • are represented by arrows and the direction of the arrow is used to represent electron spin • fill orbitals in order of increasing energy beginning with 1s, then2s and 2p

5. Electrons in Orbital Diagrams Orbitals can hold a maximum of two electrons. Within sublevels that contain multiple orbitals, one electron is placed in each orbital with parallel spins before the electrons are paired.

6. Electron Configurations Chemists use a notation called the electron configuration to indicate placement of electrons in an atom. The lowest energy sublevel is written first, then sublevels with increasing energies. The number of electrons in each sublevel is written as a superscript.

7. Period 1: Hydrogen and Helium The 1s is written first; it has the lowest energy.

8. Period 2: Lithium to Neon • Period 2 begins with lithium, which has three electrons, 1s2 2s1. • After the 2s is filled, the 2p orbitals are filled. • One electron is placed in each p orbital before they are paired. • An abbreviated configuration uses a noble gas in brackets to represent the filled electron configuration of that noble gas. [He] 2s1

9. Period 2: Lithium to Neon

10. Period 2: Lithium to Neon

11. Guide to Drawing Orbital Diagrams

12. Sample Problem Draw the orbital diagram for nitrogen. Step 1 Draw boxes to represent the occupied orbitals. Nitrogen has an atomic number of seven, which means it has seven electrons. Draw boxes to represent the 1s, 2s, and 2p orbitals.

13. Sample Problem Draw the orbital diagram for nitrogen. Step 2Place a pair of electrons in the last occupied sublevel in separate orbitals. We place the remaining three electrons in the 2s orbitals.

14. Sample Problem Draw the orbital diagram for nitrogen. Step 3 Place remaining electrons with opposite spins in each filled orbital. First we place a pair of electrons with opposite spins in the 2p orbitals, with arrows in the same direction.

15. Period 3: Sodium to Argon [Ne] is used to represent 1s2 2s2 2p6.

16. Period 3: Sodium to Argon

17. Learning Check Draw the abbreviated orbital diagram for aluminum, [Ne] 3s2 3p1.

18. Solution Draw the abbreviated orbital diagram for aluminum, [Ne] 3s2 3p1. 1. The preceding noble gas is Ne; we use thisto represent 1s22s2 2p6. 2. Fill the 3s, and add the last electron to the3p sublevel. [Ne]