Chapter 5: The Periodic Law

Section 1: History of the Periodic Table

Italian chemist Stanislao Cannizzaro presented a convincing method for accurately measuring the relative mass of atoms. Russian chemist Dmitri Mendeleev created a table in which elements with similar properties were grouped together - a periodic table of elements. The best way to do this he found was to organize the elements according to their increasing atomic mass.

English chemsit Henry Moseley improved Mendeleev's periodic table, as he ordered the elements according to atomic number. He found that you were able to see a pattern in the properties better when ordered as so. Mendeleev's principle of chemical periodicity is correcly stated in the periodic law: the physical and chemical properties of the elements are periodic functions of their atomic numbers.

The periodic table is an arrangement of the elements in order of their atomic numbers so that the elements with similar properties fall in the same column, or group. The noble gases are elements of Group 18. The lanthanides are rare-earth elements, whose atomic numbers range from 58-71. The actinides have atomic numbers from 89-103.

Section 2: Electron Configuration and the Periodic Table

Based upon the electron configuration of the elements the table can be divided into four blocks. These blocks represent the different sublevels of electron configuration.

The s-block elements:
  • Groups 1-2
  • Electron configuration: ns1,2
  • Contains the alkali metals (Group 1), and alkaline-earth metals (Group 2)
  • Very reactive metals; Group 1 is more reactive than Group 2, but both do not exist in nature as free elements because they are too reactive.

The d-block elements:
  • Groups 3-12
  • Electron configuration: (n-1)d1-10ns0-2
  • transition elements: typical metallic properties
  • Good Conductors of electricity and have a high luster; less reactive than the s-block elements; many exist in nature as free elements.

The p-block elements:
  • Groups 13-18
  • Electron configuration: ns2np1-6
  • Combine with s-block elements to become the main-group elements
  • Includes nonmetals, metalloids, halogens (Group 17), and noble gases (Group 18).

The f-block elements:
  • Lanthanides and Actinides
  • Between Groups 3 and 4.
  • Between Periods 6 and 7.
  • 14 in each; highly similar properties; resemble Group 2 elements.

external image periodic_table_blocks_alone.jpg

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Section 3: Electron Configuration and Periodic Properties

  • Atomic Radii:One-half the distance between nuclei of identical atoms bonded together.
    • Period Trend- Decrease across a period.
    • Group Trend- Increase down a group.
  • Ionization Energy: Energy required to remove one electron from a neutral atom of an element.
    • Period Trend- Increase across period.
    • Group Trend- Decrease down a group.
  • Electron Affinity: Energy change that occurs when an electron is acquired by a neutral atom.
    • Period Trend- Becomes more negative across a period.
    • Group Trend- More difficult to add electrons down a group.

  • Ionic Radii: Common ions of elements and their radii.
  • Cation- positive ion.
  • Anion- negative ion.
    • Period Trend- Left tends to form cations, while the right tends to form anions.
    • Group Trend- Increase of ionic radii down a group

  • Electronegativity: Measure of the ability of an atom in a chemical compound to attract electrons from another atom in the compound.
    • Period Trend- Increase along a period.
    • Group Trend- Decrease down a group, or remain the same.

Student Created Test Items

1. Define periodic law.

2. How many blocks are on the periodic table? What are they called?

3. What group contains the most reactive nonmetals?

4. How many different types of metals are on the periodic table? What are they?

5. True/False, ionization is the energy required to remove one electron from a neutral atom of an element.

6. What does O2- mean?

7. What does Li+ mean?

8. What's the electron configuration for O2-?

9. What's the electron configuration for Li+?

10. Is Iodine an alkali metal, Halogen, or Noble gas?

11. What is an ion?

12. What is a positive ion called?

13. What is a negative ion called?

14. Valence electrons are found in which blocks?

15. Which halogen has the highest atomic radius?

16. Which halogen has the lowest atomic radius?

17. Does the atomic radius increase or decrease going down a group?

18. Which alkaline earth metal has the highest atomic radius?

19. Why are metals more likely to form positive ions and nonmetals more likely to form negative ions?

20. What makes the Noble gases so unreactive?

21. Explain why the atomic radii periodic trend gets smaller as moving left to right across the periods and gets larger as moving down the group.

22. Name which groups include the s, p, d, and f blocks in the periodic table.

23. Why does electronegativity increase as you move left to right across the periodic table?

24. What is the difference between a cation and a anion?

25. What is electron affinity?

26. Does atomic radii get smaller or larger as you go across the periodic table?

27. Elements on the chart going from left to right will increase or decrease in electronegativity?

28. Electronegativity is what?

29. Using patterns of atomic radius infer which element will have the largest radius.

30. What groups does the p block range between?

31. Why are valence electrons important? Where are they located on an atom?

32. Explain why as you take more electrons off during ionization, it requires more energy, and how it changes are you go left to right and down.

33. In what block are non-metals located?

34. Write the electron configuration for F-

35. What is the periodic law?

36. What is the trend of first ionization energies on the periodic table?

37. In the ion: Na+ , are the electrons being added or subtracted?

38. are electrons available to be lost, gained, or shared in the formation of chemical compounds.

39. __ may be defined as one half the distance between the nuclei of identical atoms that are bonded together.

40. What block are the transition elements in ?

41. what are the properties of the noble gases?

42. how does an electron configuration change from a positive to negative charged ion?

43. What are the outermost sub levels?

44. What are actinides?

45. What is ionization energy?

46. What happens to effective nuclear charge as you go across periods and and down groups?

47. What are the elements of group 2 called?

48. How was the modern periodic table arranged?

49. What group of elements has the highest ionization energies?

50. Why are halogens highly reactive?

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