Discovering a Pattern

2. Discovering a Pattern • In 1869, Russian chemist Dmitri Mendeleev arranged the elements in order of increasing atomic mass. • His Periodic table showed that • Elements with similar properties occurred in a repeating pattern • There were gaps in its pattern • He could predict the properties of the missing elements • By 1886, all of the gaps had been filled and Mendeleev’s predictions were right.

3. Changing the Arrangement • A few elements’ properties did not fit in the pattern of Mendeleev’s table. • 1914: British scientist Henry Moseley found the atomic number of atoms. • Elements arranged by atomic number fit the pattern in Mendeleev’s table.

4. Vertically intoGroups Horizontally IntoPeriods Elements are arranged:

5. Why?

6. If you looked at one atom of every element in a group you would see…

7. Each atom has the same number of electrons in it’s outermost shell. • An example…

8. The group 2 atoms all have 2 electrons in their outer shells Be (Beryllium) Atom Mg (Magnesium) Atom

9. The number of outer or “valence” electrons in an atom effects the way an atom bonds. • The way an atom bonds determines many properties of the element. • This is why elements within a group usually have similar properties.

10. If you looked at an atom from each element in a period you would see…

11. Each atom has the same number of electron holding shells. An example…

12. The period 4 atoms each have 4 electroncontaining shells 4th Shell K (Potassium) Atom Kr (Krypton) Atom Fe (Iron) Atom

13. Each group has distinct properties • The periodic Table is divided into several groups based on the properties of different atoms.

14. The Periodic Table and Classes of Elements • Elements are classified as metals, nonmetals, and metalloids based on number of electrons in outer shell • an outer shell is considered complete when it contains 8 electrons • The zigzag line on the periodic table can help you recognize which elements belong in which category.

15. Group 1: Alkali Metals • Alkali metals properties: • metals • 1 electron in the outer level • very reactive • softness, color of silver, shininess, low density

16. http://www.lyon.edu/webdata/Users/DMcDowell/GenChem/alkalishow.htmlhttp://www.lyon.edu/webdata/Users/DMcDowell/GenChem/alkalishow.html Alkali Metals Soft, silvery colored metals Very reactive!!!

17. Metals • found to the left of the zigzag line • have few electrons in their outer energy level. • shiny, ductile, malleable, and are good conductors of electric current and thermal energy.

18. Alkali Metals reacting with water: • Li (Lithium) • Na (Sodium) • K (Potassium) • Rb (Rubidium) • Cs (Cesium) What would you expect from Francium?!?!

19. Group 2: Alkaline-Earth Metals • Alkaline-earth metals properties: • metals • 2 electrons in the outer level • very reactive, but less reactive than alkali metals • color of silver, higher densities than alkali metals

20. Alkaline Earth Metals Silvery-White Metals Fairly reactive Many are found in rocks in the earth’s crust

21. Group 3–12: Transition Metals • Properties of Transition Metalsvary widely but include: • metals • 1 or 2 electrons in the outer level • less reactive than alkaline-earth metals • shininess, good conductors of electric current and thermal energy

22. Transition Metals Most are good Conductors of electricity Malleable (easily bent/hammered into wires or sheets)

23. How many things can you think of that have Transition Metals in them?

25. Metalloids lie on either side of these “stairsteps” They share properties with both metals and non-metals Si (Silicon) and Ge (Germanium) are very important “semi-conductors”

26. Metalloids • border the zigzag line • have about half of a complete set of electrons in their outer energy level. • Metalloids have some properties of metals and some properties of nonmetals. • Metalloids are also called semiconductors.

27. What are semiconductors used in?

28. Nonmetals Brittle Do not conduct electricity

29. Nonmetals • to the right of the zigzag line • have an almost complete set of electrons in their outer energy level. • not shiny, ductile, or malleable, and poor conductors of electric current and thermal energy.

30. Group 13: Boron Group • Group 13 properties: • one metalloid and five metals • 3 electrons in the outer level • reactive • solids at room temperature

31. Group 14: Carbon Group • Group 14 properties: • one nonmetal, two metalloids, and two metals • 4 electrons in the outer level • reactivity varies among the elements • solids at room temperature

32. Group 15: Nitrogen Group • Group 15 properties: • two nonmetals, two metalloids, and two metals • 5 electrons in the outer level • reactivity varies among the elements • solids at room temperature (except for nitrogen, which is a gas)

33. Chapter 12 Section2 Grouping the Elements Group 16: Oxygen Group • Group 16 properties: • group contains three nonmetals, one metalloids, and one metal • 6 electrons in the outer level • reactive • solids at room temperature (except for oxygen, which is a gas)

34. Chapter 12 Section2 Grouping the Elements Hydrogen • The properties of hydrogen do not match the properties of any single group, so hydrogen is set apart. • a nonmetal • 1 electron in the outer level • reactive • colorless, odorless gas at room temperature, low density

35. Halogens Most are Poisonous Fairly reactive

36. Chapter 12 Section2 Grouping the Elements Group 17: Halogens • Halogensare the elements in Group 17. Group 17 properties: • group contains nonmetals • 7 electrons in the outer level • very reactive • poor conductors of electric current, never in uncombined form in nature

37. Chlorine Gas was used as a chemical weapon during World War I. It was used by the Nazis in World War II.

38. Chapter 12 Section2 Grouping the Elements Group 18: Noble Gases • Noble gasesare the elements in Group 18. Group 18 properties: • group contains nonmetals • 8 electrons in the outer level (except helium, which has 2) • unreactive • colorless, odorless gases at room temperature

39. Noble Gases Unreactive Gases at room temperature

40. Jellyfish lamps made with noble gases artist- Eric Ehlenberger

41. Colors Noble Gases produce in lamp tubes: • Ne (Neon): orange-red • Hg (Mercury): light blue • Ar (Argon): pale lavender • He (Helium): pale peach • Kr (Krypton):pale silver • Xe (Xenon): pale, deep blue

42. Group 3–12: Transition Metals, continued • Lanthanides and Actinides Some transition metals from Periods 6 and 7 appear in two rows at the bottom of the periodic table. Elements in the first row are called lanthanides and elements in the second row are called actinides.

43. Lanthanide Series Actinide Series

44. Chapter 12 The Periodic Tables Concept Map Use the terms below to complete the concept map on the next slide.

45. Chapter 12 The Periodic Table

46. Chapter 12 The Periodic Table

47. Standardized Test Preparation Chapter 12 1. Which of the following statements is correct for the elements shown? ALithium has the greatest atomic number. BSodium has the least atomic mass. CAtomic number decreases as you move down the column. DAtomic mass increases as you move down the column.

48. Standardized Test Preparation Chapter 12 1. Which of the following statements is correct for the elements shown? ALithium has the greatest atomic number. BSodium has the least atomic mass. CAtomic number decreases as you move down the column. DAtomic mass increases as you move down the column.

49. Standardized Test Preparation Chapter 12 2. Which of the following statements best describes the outer electrons in atoms of the elements shown? FThe atoms of each element have 1 outer-level electron. G Lithium atoms have 3 outer-level electrons, sodium atoms have 11, and potassium atoms have 19. HLithium atoms have 7 outer-level electrons, sodium atoms have 23, and potassium atoms have 39. IThe atoms of each element have 11 outer-level electrons.

50. Standardized Test Preparation Chapter 12 2. Which of the following statements best describes the outer electrons in atoms of the elements shown? FThe atoms of each element have 1 outer-level electron. G Lithium atoms have 3 outer-level electrons, sodium atoms have 11, and potassium atoms have 19. HLithium atoms have 7 outer-level electrons, sodium atoms have 23, and potassium atoms have 39. IThe atoms of each element have 11 outer-level electrons.