1. Electron Configuration

2. Objectives Describe the relationship between orbitals and energy levels for the electrons of an atom Describe the relationship between orbitals and energy levels for the electrons of an atom Describe how to write the electron configuration for an atom Describe how to write the electron configuration for an atom Explain quantum numbers and how they affect electron configuration of atoms Explain quantum numbers and how they affect electron configuration of atoms Explain why the actual electron configurations for some elements differ from those predicted by the Aufbau principle Explain why the actual electron configurations for some elements differ from those predicted by the Aufbau principle

3. Important Vocabulary Atomic orbital Atomic orbital Quantum numbers Quantum numbers Principal quantum number Principal quantum number angular momentum quantum number angular momentum quantum number Magnetic quantum number Magnetic quantum number Electron configuration Electron configuration Pauli exclusion principle Pauli exclusion principle Hund’s rule Hund’s rule Aufbau principle Aufbau principle

4. Atomic Orbitals An atomic orbital is best though of as a region of space in which there is a high probability of finding an electron An atomic orbital is best though of as a region of space in which there is a high probability of finding an electron Electrons are found in orbitals within energy levels Electrons are found in orbitals within energy levels Within each level, electrons occupy orbitals that have the lowest energy Within each level, electrons occupy orbitals that have the lowest energy 4 different kinds of orbitals 4 different kinds of orbitals s, p, d and f s, p, d and f

5. s Orbitals Are the simplest Are the simplest Are spherical in shape Are spherical in shape Have the lowest energy Have the lowest energy Hold only 2 electrons Hold only 2 electrons

6. p Orbitals Are dumbbell shaped Are dumbbell shaped They can be oriented three different ways in space They can be oriented three different ways in space Has more energy than a s orbital Has more energy than a s orbital Each p orbital can hold 2 electrons for a total of 6 electrons Each p orbital can hold 2 electrons for a total of 6 electrons

7. d & f Orbitals Are much more complex Are much more complex There are 5 possible d orbitals which are clover leaf shapes There are 5 possible d orbitals which are clover leaf shapes There are 7 possible f orbitals There are 7 possible f orbitals f orbitals have the greatest energy f orbitals have the greatest energy Each orbital holds a maximum of 2 electrons Each orbital holds a maximum of 2 electrons

8. Orbitals

9. 1 st energy level has 1 sublevel = s 1 st energy level has 1 sublevel = s So it contains 1 orbital and holds 2 electrons 2 nd energy level has 1 s orbital and 3 p orbitals 2 nd energy level has 1 s orbital and 3 p orbitals So it can hold 8 electrons 3 rd energy level has s, p, & d orbitals 3 rd energy level has s, p, & d orbitals So it can hold 18 electrons 4 th energy level has s, p, d, & f orbitals 4 th energy level has s, p, d, & f orbitals So it can hold 32 electrons Relationship between Levels & Sublevels

10. Periodic Table Orbitals

11. Quantum Numbers Scientists have defined the region in which electrons can be found by using 4 quantum numbers Scientists have defined the region in which electrons can be found by using 4 quantum numbers A quantum number is a number that specifies the properties of electrons A quantum number is a number that specifies the properties of electrons The principal quantum number, n, indicates the main energy level occupied by an electron The principal quantum number, n, indicates the main energy level occupied by an electron Values of n are positive integers Values of n are positive integers As n increases, the electron’s distance from the nucleus and its energy increases As n increases, the electron’s distance from the nucleus and its energy increases

12. orbital

13. Quantum Numbers Continued Main energy levels can be subdivided Main energy levels can be subdivided The sublevels are represented by the angular momentum quantum number, l The sublevels are represented by the angular momentum quantum number, l This number indicates the shape or type of orbital of a particular sublevel This number indicates the shape or type of orbital of a particular sublevel Chemists use a letter code for this quantum number Chemists use a letter code for this quantum number l = 0 = an s orbital l = 0 = an s orbital l = 1 = an p orbital l = 1 = an p orbital l = 2 = an d orbital l = 2 = an d orbital l = 3 = an f orbital l = 3 = an f orbital

14. Magnetic Quantum Numbers Symbolized by m Symbolized by m Is a subset of the angular quantum number Is a subset of the angular quantum number It also indicates the numbers and orientations of orbitals around the nucleus It also indicates the numbers and orientations of orbitals around the nucleus The value of m is in whole-number values but depends on the value of l The value of m is in whole-number values but depends on the value of l 1 s orbital, 3 p orbitals, 5 d orbitals and 7 f orbitals 1 s orbital, 3 p orbitals, 5 d orbitals and 7 f orbitals

15. Spin Quantum Number Symbolized by + ½ and – ½ or ↑ and ↓ Symbolized by + ½ and – ½ or ↑ and ↓ It indicates the orientation of an electron’s magnetic field relative to an outside magnetic field It indicates the orientation of an electron’s magnetic field relative to an outside magnetic field A single orbital can hold a maximum of 2 electrons, which must have opposite spins A single orbital can hold a maximum of 2 electrons, which must have opposite spins

16. Principal Quantum Number Angular Momentum Quantum Number Magnetic Quantum Numbers Spin Quantum Numbers

18. Electron Configurations Electrons in atoms tend to assume arrangements with the lowest possible energies Electrons in atoms tend to assume arrangements with the lowest possible energies An electron configuration is the written arrangement of electrons in an atom An electron configuration is the written arrangement of electrons in an atom It shows the lowest-energy arrangement of the electrons for an element It shows the lowest-energy arrangement of the electrons for an element It is a shorthand notation It is a shorthand notation 3 rules determine it 3 rules determine it

19. Pauli Exclusion Principle Was established by the German chemist Wolfgang Pauli in 1925 Was established by the German chemist Wolfgang Pauli in 1925 It states that each orbital can hold a maximum of 2 electrons It states that each orbital can hold a maximum of 2 electrons In other words, no two electrons in the same atom can have exactly the same four quantum numbers In other words, no two electrons in the same atom can have exactly the same four quantum numbers In addition, if one electron has a spin quantum number of + ½ than the other must be – ½ In addition, if one electron has a spin quantum number of + ½ than the other must be – ½

20. The Aufbau Principle Also helps to write the electron configuration for an atom Also helps to write the electron configuration for an atom It states that electrons fill orbitals that have the lowest energy first It states that electrons fill orbitals that have the lowest energy first Order for filling orbitals is as follows: Order for filling orbitals is as follows: 1s ‹ 2s ‹ 2p ‹ 3s ‹ 3p ‹ 4s ‹ 3d 1s ‹ 2s ‹ 2p ‹ 3s ‹ 3p ‹ 4s ‹ 3d

21. Hund’s Rule States that orbitals of the same n and l quantum numbers are each occupied by 1 electron before any pairing occurs States that orbitals of the same n and l quantum numbers are each occupied by 1 electron before any pairing occurs

22. Electron Configuration Example Let’s do magnesium (Mg) Let’s do magnesium (Mg) It has 12 electrons It has 12 electrons

23. Electron Configuration 1s 2 2s 2 2p 6 3s 2 or [Ne]3s 2

24. Electron Configuration Practice Let’s try a few together Let’s try a few together Na Na Ar Ar Ca Ca

25. Electron Configuration

26. Electron Configuration Practice Now you try! Now you try! F S

27. Exceptional Electron Configurations The elements after Vanadium (atomic #23) do not follow the Aufbau principle The elements after Vanadium (atomic #23) do not follow the Aufbau principle Filled energy sublevels are more stable than partially filled sublevels. Filled energy sublevels are more stable than partially filled sublevels. Exceptions to the aufbau principle are due to subtle electron-electron interactions in orbitals with very similar energies. Exceptions to the aufbau principle are due to subtle electron-electron interactions in orbitals with very similar energies. For Example: Cu and Cr For Example: Cu and Cr

28. Exceptions to Aufbau’ Principle INCORRECT CORRECT