Unit 2 – Electrons and Periodic Behavior

1. Unit 2 – Electrons and Periodic Behavior Cartoon courtesy of NearingZero.net

2. Wave-Particle Duality JJ Thomson won the Nobel prize for describing the electron as a particle. His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron. The electron is a particle! The electron is an energy wave!

3. The Wave-like Electron The electron propagates through space as an energy wave. To understand the atom, one must understand the behavior of electromagnetic waves. Louis deBroglie

4. Spectroscopic analysis of the visible spectrum… …produces all of the colors in a continuous spectrum

5. Electron transitionsinvolve jumps of definite amounts ofenergy. This produces bands of light with definite wavelengths.

6. Quantum Numbers Each electron in an atom has a unique set of 4 quantum numbers which describe it. • Principal quantum number • Angular momentum quantum number • Magnetic quantum number • Spin quantum number

7. Pauli Exclusion Principle No two electrons in an atom can have the same four quantum numbers. Wolfgang Pauli

8. Principal Quantum Number Generally symbolized by n, it denotes the shell (energy level) in which the electron is located. Number of electrons that can fit in a shell: 2n2

9. Angular Momentum Quantum Number The angular momentum quantum number, generally symbolized by l, denotes the orbital (subshell) in which the electron is located.

10. Magnetic Quantum Number The magnetic quantum number, generally symbolized by m, denotes the orientation of the electron’s orbital with respect to the three axes in space.

11. Assigning the Numbers • The three quantum numbers (n, l, and m) are integers. • The principal quantum number (n) cannot be zero. • n must be 1, 2, 3, etc. • The angular momentum quantum number (l) can be any integer between 0 and n - 1. • For n = 3, l can be either 0, 1, or 2. • The magnetic quantum number (m) can be any integer between -l and +l. • For l = 2, m can be either -2, -1, 0, +1, or +2.

12. Principle, angular momentum, and magnetic quantum numbers: n, l, and ml

13. Spin Quantum Number Spin quantum number denotes the behavior (direction of spin) of an electron within a magnetic field. Possibilities for electron spin:

14. An orbital is a region within an atom where thereis a probability of finding an electron. This is a probability diagram for the s orbital in the first energy level… Orbital shapes are defined as the surface that contains 90% of the total electron probability.

15. Sizes of s orbitals Orbitals of the same shape (s, for instance) grow larger as n increases… Nodes are regions of low probability within an orbital.

16. The s orbital has a spherical shape centered around the origin of the three axes in space. s orbital shape

17. P orbital shape There are three dumbbell-shaped p orbitals in each energy level above n = 1, each assigned to its own axis (x, y and z) in space.

18. Things get a bit more complicated with the five d orbitals that are found in the d sublevels beginning with n = 3. To remember the shapes, think of “double dumbells” d orbital shapes …and a “dumbell with a donut”!

19. Shape of f orbitals

20. Orbital filling table

21. Electron configuration of the elements of the first three series

22. Irregular confirmations of Cr and Cu Chromium steals a 4s electron to half fill its 3d sublevel Copper steals a 4s electron to FILL its 3d sublevel

23. Mendeleev’s Periodic Table Dmitri Mendeleev

24. Modern Russian Table

25. Stowe Periodic Table

26. A Spiral Periodic Table

27. “Mayan” Periodic Table

28. Period The Periodic Table Group or Family Group or family Period

29. The Properties of a Group: the Alkali Metals • Easily lose valence electron • (Reducing agents) • React violently with water • Large hydration energy • React with halogens to form • salts

30. Properties of Metals • Metals are good conductors of heat and electricity • Metals are malleable • Metals are ductile • Metals have high tensile strength • Metals have luster

31. Examples of Metals Potassium, K reacts with water and must be stored in kerosene Copper, Cu, is a relatively soft metal, and a very good electrical conductor. Zinc, Zn, is more stable than potassium Mercury, Hg, is the only metal that exists as a liquid at room temperature

32. Propertiesof Nonmetals Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element. • Nonmetals are poor conductors of heat and • electricity • Nonmetals tend to be brittle • Many nonmetals are gases at room temperature

33. Examples of Nonmetals Microspheres of phosphorus, P, a reactive nonmetal Sulfur, S, was once known as “brimstone” Graphite is not the only pure form of carbon, C. Diamond is also carbon; the color comes from impurities caught within the crystal structure

34. Properties of Metalloids Metalloids straddle the border between metals and nonmetals on the periodic table. • They have properties of both metals and nonmetals. • Metalloids are more brittle than metals, less brittle than most nonmetallic solids • Metalloids are semiconductors of electricity • Some metalloids possess metallic luster

35. Silicon, Si – A Metalloid • Silicon has metallic luster • Silicon is brittle like a nonmetal • Silicon is a semiconductor of electricity Other metalloids include: • Boron, B • Germanium, Ge • Arsenic, As • Antimony, Sb • Tellurium, Te

36. Determination of Atomic Radius: Half of the distance between nucli in covalently bonded diatomic molecule "covalent atomic radii" Periodic Trends in Atomic Radius • Radius decreases across a period Increased effective nuclear charge due to decreased shielding • Radius increases down a group Addition of principal quantum levels

37. Table of Atomic Radii

38. Ionization Energy - the energy required to remove an electron from an atom • Increases for successive electrons taken from • the same atom • Tends to increase across a period Electrons in the same quantum level do not shield as effectively as electrons in inner levels Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove • Tends to decrease down a group Outer electrons are farther from the nucleus

39. Table of 1st Ionization Energies

40. Ionization of Magnesium Mg + 738 kJ  Mg+ + e- Mg+ + 1451 kJ  Mg2+ + e- Mg2+ + 7733 kJ  Mg3+ + e-

41. Another Way to Look at Ionization Energy

42. Electronegativity A measure of the ability of an atom in a chemical compound to attract electrons • Electronegativities tend to increase across • a period • Electronegativities tend to decrease down a • group or remain the same

43. Periodic Table of Electronegativities

44. Summation of Periodic Trends

45. Ionic Radii • Positively charged ions formed when • an atom of a metal loses one or • more electrons Cations • Smaller than the corresponding • atom • Negatively charged ions formed • when nonmetallic atoms gain one • or more electrons Anions • Larger than the corresponding • atom

46. Table of Ion Sizes