Chapter 5 The Periodic Table

1. Chapter 5The Periodic Table

2. 5.1 Organizing the Elements: • Key Concepts: ·Mendeleev arranged the elements into rows in order of ­­­­­­­­­­­­ increasing mass so that elements with similar properties were in the same column. ·The close match between Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be.

3. Why is the Periodic Table important to me? • The periodic table is the most useful tool in chemistry. • You get to use it on quizzes and tests! • It organizes lots of information about all the known elements.

4. Pre-Periodic Table Chemistry … • …was a mess!!! • No organization of elements. • Imagine going to a grocery store with no organization!! • Difficult to find information. • Chemistry didn’t make sense.

5. Dmitri Mendeleev: Father of the Table • Previous attempts to organize known elements failed to work for all known elements at the time • Russian Chemist and teacher, Dmitri Mendeleev, discovered a way • Found a way to approach the problem when playing his favorite card game, a version of solitaire (organization was the key) • Solitaire…??????

6. How does the game of solitaire work???

8. Dmitri Mendeleev: Father of the Table HOW HIS WORKED… • Put elements in rows by increasing atomic weight. • Elements with similar properties were in the same column. • Put elements in columns by the way they reacted.

9. Mendeleev’s Periodic Table • Periodic Table: an arrangement of elements in columns, based on a set of properties that repeat from row to row

10. Mendeleev’s Prediction • Table was not complete, not all elements had yet been discovered • He left gaps/spaces in his table for those elements • He was NOT the first to organize the elements in the form of a table • He was the FIRST to offer good explanations for how the properties of an element were related to its location in his table • He used the gaps in his tables to predict properties of undiscovered elements • Other scientists used the predictions to help in their search for undiscovered elements

11. Evidence Supporting Mendeleev’s Table • The close match between Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be • With the periodic table, chemists could do more than predict the properties of new elements – they could explain the chemical behavior of different groups of elements!!!

12. 5.2  The Modern Periodic Table

13. The Current Periodic Table • Mendeleev wasn’t too far off. • Now the elements are put in rows by increasing ATOMIC NUMBER!! • The horizontal rows are called periods and are labeled from 1 to 7. • The vertical columns are called groups are labeled from 1 to 18.

14. PERIODS • Period: A rowin a periodic table of elements (left to right) • To understand the structure of the table, think what happens as the atomic number increases: • Reminder: Atomic Number = Number of Protons • First energy level has ONLY 1 orbital • The 1 e- in a hydrogen atom and 2 e- in a helium atom can fit in this orbital (first energy level) • This is why H and He are in Period 1

15. PERIODS • Lithium, 1st element in Period 2, has one of its the three electrons in the second energy level • This is why lithium is the first element in Period 2 • Sodium, 1st element in Period 3, has one e- in its third energy level • Potassium, 1st element in Period 4, has 1 e- in its fourth energy level • This pattern applies to ALL the elements in the 1st column on the table 

16. Families (groups) on the Periodic Table • Columns are also grouped into families (or groups). • Families may be one column, or several columns put together. • Families have names (Just like your family has a common last name.)

17. Groups • Group: A column in a periodic table of elements • Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups

18. Groups • Periodic Law: the pattern of repeating properties displayed by elements in the periodic table • Elements within a group have similar properties: • Similar e- configurations (see example above – first column of the table) • Electron configuration determines an elements chemical properties

19. Various Trends of the Periodic Table

20. Atomic Mass • Atomic mass is a value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes.

21. Atomic Mass Units • Mass of an atom in grams is EXTREMELY small • Scientists came up with an easier way to talk about mass • Chose one isotope to serve as a standard • Scientists assigned 12 atomic mass units (amu’s) to the carbon-12 atom (which has 6P and 6N) • Atomic Mass Unit (amu): 1/12 the mass of a carbon-12 atom

22. An Example…Isotopes of Chlorine • Chlorine has an atomic number of 17 and an atomic mass of 35.453 atomic mass units • Where does the number 35.453 come from??? • There are two natural isotopes of Chlorine: • Chlorine-35 which has 17 protons and 18 neutrons • Chlorine-37 which has 17 protons and 20 neutrons

23. It’s a weighted average of the isotopes • Atomic masses come from an average of the isotopes for a given element that exist in nature • The value for atomic mass is known as a “weighted average” • Cl-35 occurs 3 times as often as Cl-37 • Take an average of those numbers: (3 × 35) + (1 × 37) ----------------------------- = 35.453 4

24. Classes of Elements • Elements are classified as metals, nonmetals, and metalloids.

25. Metals

26. Metals • Metals: elements that are good conductors of electric current and heat. • Properties of Metals: • Except for mercury, metals are solid at room temperature • Most metals are malleable • Many metals are ductile (can be drawn into thin wires) • Some metals are extremely reactive* (page 135, figure 10) • *Meaning they easily combine chemically with other elements

28. Transition Metals • Transition Metals: metals in groups 3-12, form a bridge between the elements on the left and right sides of the tables. • Examples: copper and silver • Some of the first elements discovered • Ability to form compounds with distinctive colors (page 137  production of colored glass) • Includes the lanthanide and actinide series (at the bottom of the table)

31. Nonmetals

32. Nonmetals • Nonmetals: elements that are poor conductors of heat and electric current • Properties opposite those of metals • Low boiling points • Most are gases at room temperature • Nonmetals that are solid at room temperature tend to be brittle (will shatter) • Some very reactive, some not at all, some fall somewhere in between • Fluorine (in Group 17) is the most reactive nonmetal (found in toothpaste)

34. Metalloids

35. Metalloids • Metalloids: elements with properties that fall betweenthose of metals and nonmetals • Ability to conduct electric current varies with temperature • Pure silicon (Si) and germanium (Ge) are good insulators at low temperatures and good conductors at high temps.

38. Variation Across a Period • Across a period from left to right, the elements become less metallic and more nonmetallic in their properties • Most reactive metals on left side • Most reactive nonmetals on the right side (in Group 17) • Period 3 elements (left to right) provide an example of this (page 138, Figure 13)

39. 5.3  Representative Groups

40. Hydrogen… • Why is hydrogen (H) on the left side of the table with the active metals? • Hydrogen’s location is related to its electron configuration, not its properties!!!

41. Patterns of Electron Configuration • Wonder why there are 2 numbering schemes on the periodic table? • When the ‘A’ groups are numbered 1-8, they provide a reminder about the electron configurations of the elements in those groups • The number of an ‘A’ group matches the number of valance electrons in an electron configuration for an element in that group

42. Valence Electrons • Valence Electron: an electron that is in the highest occupied energy level of an atom • Valence electrons play a key role in chemical reactions • Properties vary across a period because the number of valence electrons increases from left to right • Elements in a group have similar properties because they have the same number of valence electron • Hydrogen is on far left of table because it has one valence electron, just like the rest of the elements in that column

43. Valence Electrons

44. Valence Electrons  Lewis Structure

45. Hydrogen- Yellow • Hydrogen belongs to a family of its own. • Hydrogen is a diatomic, reactive gas. • Hydrogen was involved in the explosion of the Hindenberg. • http://www.youtube.com/watch?v=F54rqDh2mWA • Hydrogen is promising as an alternative fuel source for automobiles.

47. Alkali Metals- Lt. Blue • 1st column on the periodic table (Group 1 /1A) not including hydrogen. • Very reactive metals, always combined with something else in nature (like in salt).

48. Alkali Metals • Single valence electron • Soft enough to cut with a butter knife. • The reactivity of alkali metals increases from the top of Group 1A to the bottom • Lithium (Li) down through Francium (Fr) • http://www.youtube.com/watch?v=m55kgyApYrY