An Introduction to the Periodic Table

1. An Introduction to the Periodic Table Foundations and Applications

2. A little introduction… • The basic Periodic Table that you are familiar with today was developed by Dmitri Mendeleev in the latter part of the nineteenth century (1872) • His basic ideas has stood the test of time, even though his periodic table has been greatly modified over the past 140 years.

3. A Little History • By 1789, with the publication of The Elements, by Lavoisier (French), over 25 distinct elements had been identified. Nine of these had been discovered in the past 30 years. • 20 more elements were discovered in the next 20 years. • It was beginning to get difficult to keep track of them all.

4. History, cont. • In 1808, Dalton( English) had noted that each element could combine with other elements in certain fixed ratios of mass. This implied that elements combined in fixed units of matter that he called atoms. • Atoms of each element had a distinct mass. Oxygen seemed to be 16 times heavier than the lightest element, hydrogen. • If Hydrogen was set to have a mass of 1, then oxygen would have a mass of 16.

5. history…, cont. • Mendeleev based his table on two basic ideas: • The elements can reasonably be listed in order of increasing atomic weight • When that is done, the chemical properties recur periodically • Although there were errors made, his basic ideas have worked out well.

6. The Need to Organize • By the mid-1800’s, over 50 elements had been discovered. • They had a wide variety of properties, including mass, state, combining power with other elements, texture, color, etc. • To keep track of all of this information, chemists needed a way of classifying the elements • But, it was not clear which properties were important and which were not.

7. Ways to Organize • One way to organize the elements was by how they combined with others. • Some elements combined with chlorine in a 1:1 ratio • Li, Na, K, Cu, Rb, Ag • Other elements combined with chlorine in a 1:2 ratio • Be, Mg, Ca, Zn, Sr, Cd

8. Ways to Organize, cont. • Other ways to organize included • How they combined with other elements • Color and texture • Conductivity and malleability • But the easiest way to organize them was by listing them by mass.

9. B H Li P Ti V S C N O F K Si Mg Na Ca Cr Al Cl Listing by mass • This is what the list would look like in 1872: Be 1 7 9 11 12 14 16 19 23 24 27 29 31 32 35 39 40 48 51 52 And so on…

10. O F N B C Ti V K P Li H S Mg Na Al Ca Cl Cr Si Li2O Na2O K2O BeO MgO CaO Al2O3 B2O3 CO2 SiO2 Repeating Patterns • Some of the elements, when listed by mass, had properties that repeated themselves: • For example by combining powers w/oxygen Be

11. SiH4 CH4 V H Li P S F Ti C B N O K Na Al Mg Ca Si Cr Cl NH3 PH3 H2O H2S HF HCl Repeating Patterns, cont. • Or by it’s combing with hydrogen ions: Be

12. NH3 PH3 H2O C H Li P S V K Ti B N O F Ca Mg Cr Al Si Cl Na H2S HF HCl LiCl NaCl KCl BeCl2 MgCl2 CaCl2 AlCl3 BCl3 Grouping Repeated Patterns • These repeated patterns can be grouped together: Be

13. C F N B P S O Ti K V H Li Al Mg Na Cl Ca Cr Si Be Grouping Repeated Patterns, cont • The pattern seems to repeat periodically • This can allow you to rearrange the list of elements into a table, with each new line being the start of a new period.

14. B H Li P Ti V S C N O F K Al Cl Ca Cr Na Mg Si Some problems • Some of the elements appeared to be missing (perhaps undiscovered.) Be Missing space, since Ca acts like Mg and Be, and Ti acts like Si and C

15. His Table, 1871

16. N Rb K Zn Li P S V H Zr C B As O F Nb Ti Ca Cr Pd Si Ni Mg Na Mn Al Fe Cl Y Cu Mo Rh Ru Sr Br Se Co Problems, cont. • Some of the periods appeared to have 10 elements in them, not 7, The reason was not clear. Be

17. N Rb K Zn Li P S V H Zr C B As O F Nb Ti Ca Cr Pd Si Ni Mg Na Mn Al Fe Cl Y Cu Mo Rh Ru Sr Br Se Co Problems, cont. • Some of the elements had variable combining power (the transition elements) Be

18. O Li H Ti Ne P S V K He C B N Zn F Zr Rb Nb As Mn Ar Cr Cl Cu Al Mg Na Fe Si Co Ru Kr Ca Mo Y Pd Rh Sr Br Se Ni Other Problems • The Noble Gas elements had not yet been discovered, and so were not included: Be

19. B Li H P Ne V K Ti As He C Zn N O F Zr Rb Nb S Mn Ar Cr Cl Cu Al Mg Na Fe Si Co Br Kr Ca Mo Y Rh Ru Sr Se Pd Ni Modern Table • A break was added to the 2nd and third periods: Be

20. O Li H Ti Ne P S V K He C B N Zn F Zr Rb Nb As Mn Ar Cr Cl Cu Al Mg Na Fe Si Co Ru Kr Ca Mo Y Pd Rh Sr Br Se Ni Changes in the Modern Table • The long rows were combined with the shorter ones: Be

21. Sc Tc Ga Ge P Li H Xe At Ag Gd V Ty Dy Er Ho Tm Pb K As Yb Fr Lr Sn In Sb Te Ti I Nb He Zr Rb Cd Zn Ra Th S U Cs Hf Rn Hg C B Ta N F Ne Ce La Pr Ac O Po Nd Tl Np Pu Bi Am Bk Cf Es Cm Fm Sm Eu Pm Au Md Ru Rh Pd Mo Ar Rh Cu Pd Y Lu Br Sr Se Mn W Ca Cr Ba Na Al Cl Fe Si Kr Co Ru Mg Ni No Pa Finishing Touches New Elements are added Periods are completed New types of metals, the Rare Earths are discovered Be Re

22. The Modern Table • The elements are listed in atomic number ( not atomic mass). That changes the order of 3 pairs of elements. • They are grouped together by electron configuration of the outermost sub-levels (what can be called the valence electrons.) • The elements are placed in rows (called periods), where the beginning of the row signals a new energy level in the electron configuration. • The table has 18+ columns (where each column is called a “family” or “group”) The columns are usually referred as a group number.

23. S Block P Block D Block F Block The Modern Table