2. Timberlake LecturePLUS 2000 Characteristics of Atoms Atoms are composed of protons, neutrons, and electrons. Protons and neutrons are located in the nucleus (center of the atom). Electrons are located outside of the nucleus.

3. Quantum Model We learned about: – Dalton’s atomic theory – J.J. Thompson’s plum pudding model of the atom – Rutherford’s model of the atom – Bohr model of the atom The model used today is called the quantum model

4. Orbitals are represented by a letter (s, p, d, f, …)

10. Timberlake LecturePLUS 2000 Describing Electrons There are two ways to express the number and location of electrons in an atom: – Orbital Diagrams – Electron Configurations

11. Timberlake LecturePLUS 2000 Orbital Diagrams Visual representation of how electrons are placed in orbitals. Electrons are represented by arrows. In an orbital diagram, electrons have opposite spins (designated by opposite arrow directions).

12. Timberlake LecturePLUS 2000 Blank Orbital Diagram Fill in the lowest energy orbitals first! Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f

13. Timberlake LecturePLUS 2000 Electron Configuration Tells us the most likely position of where electrons can be found. It is like the address of an electron. Electron configurations are used instead of orbital diagrams because they are less cumbersome.

14. Timberlake LecturePLUS 2000 Steps for filling in an Orbital Diagram 1. Identify the number of electrons. 2. Fill in the orbital diagram using the following rules: A. Aufbau Principle-Fill in the lowest energy orbitals first. B. Pauli Exclusion Principle-Each orbital (block) can contain 2 arrows. The arrows must be pointed in opposite directions. C. Hund’s Rule Every orbital in a subshell must have one electron in it before any one orbital can be filled with a second electron.

15. Timberlake LecturePLUS 2000 Orbital Diagrams: Example #1 Draw an orbital diagram for H. Hydrogen has 1 electron. 1s 2s 2p 3s The electron configuration is then: 1s 1

16. Timberlake LecturePLUS 2000 Orbital Diagrams: Example #2 Draw an orbital diagram for B. Boron has 5 electrons. 1s 2s 2p 3s The electron configuration is then: 1s 2 2s 2 2p 1

17. Timberlake LecturePLUS 2000 Orbital Diagrams: Example #3 Draw an orbital diagram for C. Carbon has 6 electrons. 1s 2s 2p 3s The electron configuration is then: 1s 2 2s 2 2p 2

18. Timberlake LecturePLUS 2000 Orbital Diagrams: Example #4 Draw an orbital diagram for O. Oxygen has 8 electrons. 1s 2s 2p 3s The electron configuration is then: 1s 2 2s 2 2p 4

19. Timberlake LecturePLUS 2000 Practice Draw an orbital diagram and write the electron configuration for the following elements: 1. He 2. Li 3. N 4. F 5. S

20. Timberlake LecturePLUS 2000 He Helium has 2 electrons. 1s2s 2p3s The electron configuration is then: 1s 2

21. Timberlake LecturePLUS 2000 Li Lithium has 3 electrons. 1s2s 2p3s The electron configuration is then: 1s 2 2s 1

22. Timberlake LecturePLUS 2000 N Nitrogen has 7 electrons. 1s2s 2p3s The electron configuration is then: 1s 2 2s 2 2p 3

23. Timberlake LecturePLUS 2000 F Fluorine has 9 electrons. 1s2s 2p3s The electron configuration is then: 1s 2 2s 2 2p 5

24. Timberlake LecturePLUS 2000 S Sulfur has 16 electrons. 1s 2s 2p 3s 3p The electron configuration is then: 1s 2 2s 2 2p 6 3s 2 3p 4

27. Timberlake LecturePLUS 2000 More Practice Write the electron configuration for each: A. Cl B. Sr C. I

28. Timberlake LecturePLUS 2000 Solution Write the electron configuration for each: A. Cl (17 electrons) 1s 2 2s 2 2p 6 3s 2 3p 5 B. Sr (38 electrons) 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 C. I (53 electrons) 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 5

29. Noble Gas Abbreviated Notation He Ne Ar Kr Xe

30. Example Write the noble gas abbreviated electron configuration for oxygen (O). 1.) The noble gas that occurs before O is He. 2.) Start with [He]. 3.) Finish writing the electron configuration from helium: [He]2s 2 2p 4

31. Example Write the noble gas abbreviated electron configuration for Silicon (Si). The noble gas that occurs before Si is Ne. Start with [Ne]. Finish writing electron configuration from Ne: [Ne]3s 2 3p 2

32. Example Write the noble gas abbreviated electron configuration for Gallium (Ga). The noble gas that occurs before Ga is Ar. Start with [Ar]. Finish writing electron configuration from Ar: [Ar]4s 2 3d 10 4p 1

33. Write the Noble-Gas abbreviated electron configuration for the following: a.) S: b.) Cd: c.) Fe: d.) Br:

34. Write the Noble-Gas abbreviated electron configuration for the following: a.) S: [Ne]3s 2 3p 4 b.) Cd: [Kr]5s 2 4d 10 c.) Fe: [Ar]4s 2 3d 6 d.) Br: [Ar]4s 2 3d 10 4p 5