1. Tro, Principles of Chemistry: A Molecular Approach Chapter 8 Periodic Properties of the Elements Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA Principles of Chemistry: A Molecular Approach, 1 st Ed. Nivaldo Tro

2. Tro, Principles of Chemistry: A Molecular Approach2 Electron Spin Experiments by Stern and Gerlach showed that a beam of silver atoms is split in two by a magnetic field. The experiment revealed that electrons spin on their axis. As they spin, they generate a magnetic field. Spinning charged particles generate a magnetic field. If there is an even number of electrons, about half the atoms will have a net magnetic field pointing “north” and the other half will have a net magnetic field pointing “south.”

3. Tro, Principles of Chemistry: A Molecular Approach3 The Property of Electron Spin Spin is a fundamental property of all electrons. All electrons have the same amount of spin. The orientation of the electron spin is quantized—it can only be in one direction or its opposite. spin up or spin down

4. Tro, Principles of Chemistry: A Molecular Approach4 Spin Quantum Number, m s Spin quantum number describes how the electron spins on its axis. spin up or spin down Spins must cancel in an orbital. paired m s can have values of +½ or −½. By convention, a half-arrow pointing up is used to represent an electron in an orbital with spin up.

5. Tro, Principles of Chemistry: A Molecular Approach5 Pauli Exclusion Principle No two electrons in an atom may have the same set of four quantum numbers. Therefore, no orbital may have more than two electrons, and they must have opposite spins. Knowing the number of orbitals in a subshell allows us to determine the maximum number of electrons in the sublevel. s subshell has one orbital; therefore, it can hold two electrons. p subshell has three orbitals; therefore, it can hold six electrons. d subshell has five orbitals; therefore, it can hold 10 electrons. f subshell has seven orbitals; therefore, it can hold 14 electrons.

6. Tro, Principles of Chemistry: A Molecular Approach6 Allowed Quantum Numbers

7. Tro, Principles of Chemistry: A Molecular Approach Quantum Numbers of Helium’s Electrons Helium has two electrons. Both electrons are in the first energy level. Both electrons are in the s orbital of the first energy level. Since they are in the same orbital, they must have opposite spins. 7

8. Tro, Principles of Chemistry: A Molecular Approach8 Electron Configurations The ground state of the electron is the lowest energy orbital it can occupy. The distribution of electrons into the various orbitals in an atom in its ground state is called its electron configuration. The number designates the principal energy level. The letter designates the sublevel and type of orbital. The superscript designates the number of electrons in that sublevel. He = 1s 2

9. Tro, Principles of Chemistry: A Molecular Approach9 Orbital Diagrams We often represent an orbital as a square and the electrons in that orbital as arrows. The direction of the arrow represents the spin of the electron. unoccupied orbital orbital with 2 electrons orbital with 1 electron

10. Tro, Principles of Chemistry: A Molecular Approach10 Sublevel Splitting in Multielectron Atoms The sublevels in each principal energy shell of hydrogen all have the same energy. or other single-electron systems We call orbitals with the same energy degenerate. For multielectron atoms, the energies of the sublevels are split. caused by electron–electron repulsion The lower the value of the l quantum number, the less energy the sublevel has. s (l = 0) < p (l = 1) < d (l = 2) < f (l = 3)

11. Tro, Principles of Chemistry: A Molecular Approach11 Penetrating and Shielding The radial distribution function shows that the 2s orbital penetrates more deeply into the 1s orbital than does the 2p. The weaker penetration of the 2p sublevel means that electrons in the 2p sublevel experience more repulsive force and are more shielded from the attractive force of the nucleus. The deeper penetration of the 2s electrons means that electrons in the 2s sublevel experience a greater attractive force to the nucleus and are not shielded as effectively. The result is that the electrons in the 2s sublevel are lower in energy than the electrons in the 2p sublevel.

12. Tro, Principles of Chemistry: A Molecular Approach12 Penetration and Shielding

13. Tro, Principles of Chemistry: A Molecular Approach13 Energy 1s1s 7s7s 2s2s 2p2p 3s3s 3p3p 3d3d 6s6s 6p6p 6d6d 4s4s 4p4p 4d4d 4f4f 5s5s 5p5p 5d5d 5f5f Notice the following: 1.Because of penetration, sublevels within an energy level are not degenerate. 2.Penetration of the fourth and higher energy levels is so strong that their s sublevels are lower in energy than the d sublevels of the lower energy level. 3.The energy difference between levels becomes smaller for higher energy levels (and can cause anomalous electron configurations for certain elements).

14. Tro, Principles of Chemistry: A Molecular Approach14 Filling the Orbitals with Electrons Energy shells fill from lowest energy to highest. Sublevels fill from lowest energy to highest. s → p → d → f aufbau principle Orbitals that are in the same sublevel have the same energy. no more than two electrons per orbital Pauli exclusion principle When filling orbitals that have the same energy, place one electron in each before completing pairs. Hund’s rule

15. Tro, Principles of Chemistry: A Molecular Approach15 Electron Configuration of Atoms in Their Ground State The electron configuration is a listing of the subshells in order of filling with the number of electrons in that subshell written as a superscript. Kr = 36 electrons = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 A shorthand way of writing an electron configuration is to use the symbol of the previous noble gas in brackets to represent all the inner electrons, then just write the last set. Rb = 37 electrons = 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1 = [Kr]5s 1

16. Tro, Principles of Chemistry: A Molecular Approach16 Order of Subshell Filling in Ground State Electron Configurations 1s1s 2s2s2p2p 3s3s3p3p3d3d 4s4s4p4p4d4d4f4f 5s5s5p5p5d5d5f5f 6s6s6p6p6d6d 7s7s Start by drawing a diagram with each energy shell on one row, and list the subshells (s, p, d, f) for that shell in order of energy (left to right). Next, draw arrows down through the diagonals, looping back to the next diagonal each time.

17. Tro, Principles of Chemistry: A Molecular Approach17 Electron Configurations

18. Tro, Principles of Chemistry: A Molecular Approach18 Example—Write the full ground state orbital diagram and electron configuration of manganese. Mn: Z = 25; therefore, 25 e − Based on the order of subshell filling, we will need the first 7 subshells 1s1s 2s2p2p 3s3s3p3p3d3d 4s4s4p4p4d4d4f4f s subshell holds 2 e − p subshell holds 6 e − d subshell holds 10 e − f subshell holds 14 e − 2 e − +2 = 4e − +6 +2 = 12e − +6 +2 = 20e −  1s1s2s2s2p2p3s3s3p3p4s4s    Therefore, the electron configuration is 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5. +10 = 30e − 3d3d 

19. Tro, Principles of Chemistry: A Molecular Approach19 Practice—Write the full ground state orbital diagram and electron configuration of potassium.

20. Tro, Principles of Chemistry: A Molecular Approach20 Practice—Write the full ground state orbital diagram and electron configuration of potassium. K: Z = 19; therefore, 19 e − Based on the order of subshell filling, we will need the first six subshells. 1s1s 2s2p2p 3s3s3p3p3d3d 4s4s4p4p4d4d4f4f s subshell holds 2 e − p subshell holds 6 e − d subshell holds 10 e − f subshell holds 14 e − 2 e − +2 = 4e − +6 +2 = 12e − +6 +2 = 20e −  1s1s2s2s2p2p3s3s3p3p4s4s   Therefore, the electron configuration is 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1.

21. Tro, Principles of Chemistry: A Molecular Approach21 Valence Electrons The electrons in all the subshells with the highest principal energy shell are called the valence electrons. Electrons in lower energy shells are called core electrons. Chemists have observed that one of the most important factors in the way an atom behaves, both chemically and physically, is the number of valence electrons.

22. Tro, Principles of Chemistry: A Molecular Approach22 Electron Configuration of Atoms in Their Ground State Kr = 36 electrons 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 There are 28 core electrons and eight valence electrons. Rb = 37 electrons 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1 [Kr]5s 1 For the 5s 1 electron in Rb, the set of quantum numbers is n = 5, l = 0, m l = 0, m s = +½. For an electron in the 2p sublevel, the set of quantum numbers is n = 2, l = 1, m l = −1 or (0,+1), and m s = −½ or (+½).

23. Tro, Principles of Chemistry: A Molecular Approach23 Electron Configuration and the Periodic Table The group number corresponds to the number of valence electrons. The number of columns in each “block” is the maximum number of electrons that sublevel can hold. The period number corresponds to the principal energy level of the valence electrons.

24. Tro, Principles of Chemistry: A Molecular Approach24

25. Tro, Principles of Chemistry: A Molecular Approach25 s1s1 s2s2 d 1 d 2 d 3 d 4 d 5 d 6 d 7 d 8 d 9 d 10 s2s2 p 1 p 2 p 3 p 4 p 5 p6p6 f 2 f 3 f 4 f 5 f 6 f 7 f 8 f 9 f 10 f 11 f 12 f 13 f 14 f 14 d 1 12345671234567

26. Tro, Principles of Chemistry: A Molecular Approach26 Electron Configuration from the Periodic Table P = [Ne]3s 2 3p 3 P has five valence electrons. 3p33p3 P Ne 12345671234567 1A 2A 3A4A5A6A7A 8A 3s23s2

27. Tro, Principles of Chemistry: A Molecular Approach27 Transition Elements For the d block metals, the principal energy level is one less than the valence shell. one less than the period number sometimes s electron is “promoted” to d sublevel 4s4s3d3d Zn Z = 30, period 4, group 2B [Ar]4s 2 3d 10 For the f block metals, the principal energy level is two less than the valence shell. two less than the period number they really belong to sometimes there is a d electron in the electron configuration Eu Z = 63, period 6 [Xe]6s 2 4f 7 6s6s4f4f

28. Tro, Principles of Chemistry: A Molecular Approach28 Electron Configuration from the Periodic Table As = [Ar]4s 2 3d 10 4p 3 As has five valence electrons. 4s24s2 Ar 3d 10 4p34p3 As 12345671234567 1A 2A 3A4A5A6A7A 8A

29. Tro, Principles of Chemistry: A Molecular Approach29 Practice—Use the periodic table to write the short electron configuration and short orbital diagram for each of the following. Na (atomic no. 11) Te (atomic no. 52) Tc (atomic no. 43) 3s3s [Ne]3s 1 5s5s5p5p 4d4d [Kr]5s 2 4d 10 5p 4 5s5s4d4d [Kr]5s 2 4d 5

30. Tro, Principles of Chemistry: A Molecular Approach30 Anomalous Electron Configurations We know that because of sublevel splitting, the 4s sublevel is lower in energy than the 3d, and therefore the 4s fills before the 3d. But the difference in energy is not large. Some of the transition metals have anomalous electron configurations in which the (n)s only partially fills before the (n−1)d or doesn’t fill at all. Therefore, their electron configurations must be found experimentally.

31. Tro, Principles of Chemistry: A Molecular Approach31 Expected Cr = [Ar]4s 2 3d 4 Cu = [Ar]4s 2 3d 9 Mo = [Kr]5s 2 4d 4 Ru = [Kr]5s 2 4d 6 Pd = [Kr]5s 2 4d 8 Found experimentally Cr = [Ar]4s 1 3d 5 Cu = [Ar]4s 1 3d 10 Mo = [Kr]5s 1 4d 5 Ru = [Kr]5s 1 4d 7 Pd = [Kr]5s 0 4d 10 Anomalous Electron Configurations

32. Tro, Principles of Chemistry: A Molecular Approach32 Properties and Electron Configuration Elements in the same column have similar chemical and physical properties because they have the same number of valence electrons in the same kinds of orbitals.

33. Tro, Principles of Chemistry: A Molecular Approach33 Noble Gas Electron Configuration The noble gases have eight valence electrons. Except for He, which has only two electrons. We know that the noble gases are especially nonreactive. He and Ne are practically inert. The noble gases are so nonreactive because the electron configuration of the noble gases is especially stable.

34. Tro, Principles of Chemistry: A Molecular Approach34 Everyone Wants to Be Like a Noble Gas!—The Alkali Metals The alkali metals have one more electron than the previous noble gas. In their reactions, the alkali metals tend to lose their extra electron, resulting in the same electron configuration as a noble gas. forming a cation with a 1+ charge