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Periodic Table S1 The Periodic Table History of the Periodic Table I. Early attempts Made the task a little easier: Jöns Jakob Berzelius 1828 Swedish - developed a table of atomic weights - introduced letters to symbolize elements a) Johann Döbereiner 1829 German - described triads of elements (e.g. Cl, Br, I; Ca, Ba, Sr; S, Se, Te) – first indication that elements were related to one another – atomic mass is related to chemical properties Karlsruhe Congress (big Chemistry Conference) 1860 Germany b) John Newlands 1865 English - arranged elements in order of relative atomic masses; - described the Rule of Octaves – every 8th element has similar properties c) Julius Lothar Meyer 1870 German graph of atomic volume (atomic weight/density) against atomic weight periodic trends in elements’ properties; established concept of valency II. Dmitri Mendeleev a) 1869 Russian How: While writing a book on inorganic chemistry to get organized, wrote elements on notecards with some properties and atomic weight/mass: ULTIMATE SOLITAIRE arranged elements in order of atomic masses noticed a repetition of properties every 8 or 18 elements elements with similar properties in horizontal rows -1- Periodic Table S1 b) The amazing part: he predicted 3 elements not yet discovered (eka-aluminum, eka-boron, eka-silicon) c) Problems : Ar/K, Te/I, Co/Ni 1st element in each pair has greater atomic mass places reactive K in unreactive noble gases d) Importance – 1) realized elements yet to be discovered; 2) characteristics of element could be predicted from its atomic weight (and position on the tables) Properties of Some Elements Predicted by Mendeleev Predicted Elements Eka-aluminum Eka-boron Eka-silicon Element and year discovered Gallium, 1875 Scandium, 1877 Germanium, 1886 Properties Density of metal Melting point Predicted Properties 6.0 g/mL Low Observed Properties 5.96 g/mL 30oC Oxide formula Ea2O3 Ga2O3 Density of metal Oxide formula 3.5 g/mL Eb2O3 3.86 g/mL Sc2O3 Solubility of oxide Dissolves in acid Dissolves in acid Melting point Density of metal Color of metal Oxide formula High 5.5 g/mL Dark gray EsO2 900oC 5.47 g/mL Grayish white GeO2 Density of oxide Chloride formula 4.7 g/mL EsCl4 4.70 g/mL GeCl4 Discovery of the Noble Gases 1890s • Lord Rayleigh (physicist) and Sir William Ramsay (chemist) • 1894 - Argon “the lazy one”, discovered when Ramsay was trying to isolate nitrogen • 1895 - Helium – found on earth in uranium minerals (found in the sun in 1868) • 1898 - Neon “the new one”, Krypton “the hidden one”, Xenon “the alien one” • 1910 – Radon Properties: Largely unreactive, 8 electrons in valence shell, low boiling and melting points -2- Periodic Table S1 Nucleus discovered – 1910 - Rutherford predicted that the charge of an atom is proportional to its mass III. Henry Moseley 1913 English (worked with Rutherford) a) of emitted X-rays corresponded to # protons atomic number “Do other properties match atomic numbers?” Yes! arranged the periodic table by atomic #’s, not mass b) IV. Law of Atomic Numbers (Law of Chemical Periodicity) - the properties of elements are periodic functions of their atomic numbers - corrected incorrect placement of cobalt and nickel, and iodine and tellurium Glenn Seaborg 1940s American 1912-1999 a) “transuranium” elements – formation of elements beyond uranium (93-103) reorganization of periodic table to include both series of radioactive elements (lanthanides and actinides) b) note the names of elements 95-103, reflect Seaborg’s academic life – scientists and institutions (UC-Berkeley) Trends of the Periodic Table “periodic” = repeating pattern Overall theme = electrons’ positions relative to each other and the nucleus determine the following properties: 1. Atomic radius 2. Ionization energy 3. Electronegativity -3- Periodic Table S1 1. Atomic Radius ½ distance between nuclei a) Trend down a GROUP: i. larger atoms – valence e-’s are farther away from nucleus ii. shielding effect – the number of e-’s between the nucleus and valence e’s helps keep the valence e-’s farther away from the nucleus, thus the pull of the nucleus on the valence e-’s. b) Trend across a PERIOD: same principal energy level) i. for every added e-, one more p+ pull on outer e-’s by nucleus ii. not as noticeable in periods with heavier elements (inner e-‘s shield the valence e-’s greater distance between nucleus and valence e-’s) iii. shielding effect is constant across a period, as e-’s are added only to the valence, or outermost energy level -4- Periodic Table S1 Atomic Radii 1. Which groups and periods of elements are shown in the table of atomic radii? ______________________________________________________________________ 2. In what unit is atomic radius measured? __________Express this unit in m __________ 3. What are the values of the smallest and largest atomic radii shown? What elements have these atomic radii? _______________________________________________________ 4. What happens to atomic radii within a period as the atomic number increases? ______________________________________________________________________ 5. What accounts for the trend in atomic radii within a period? ______________________________________________________________________ ______________________________________________________________________ -5- Periodic Table S1 6. What happens to atomic radii within a group? ____________________________ 7. What accounts for the trend in atomic radii within a group? _______________________________________________________________________ _______________________________________________________________________ 8. a) Divide the atomic radius of Cs by the atomic radius of Li and round to 2 significant figures. Cs:Li _______________ b) Divide the atomic radius of Cs by the atomic radius of Rn and round to 2 significant figures. Cs:Rn ______________ c) Summarize your findings about a) and b) here: _____________________________ ___________________________________________________________________ 2. Ionization Energy Definition: the energy required to remove an electron from an atom in the gas phase (in J or kJ) a) Successive ionization energies for each atom (since > 1 electron can be removed) Removing each subsequent electron requires more energy Diagram - removing successive electrons from Be: -6- Periodic Table S1 Ionization Energies of Na, Mg, and Al (in kJ/mol) Successive ionization energies (kJ/mol) Element First Second Third Fourth Na 496 4,562 6,912 9,543 Mg 738 1,451 7,733 10,540 Al 578 1,817 2,745 11,577 1. What happens to the values of the successive ionization energies of an element? ___________________________________________________________________ 2. How is a jump in ionization energy related to the valence electrons of the element? ___________________________________________________________________ ___________________________________________________________________ -7- Periodic Table S1 1. What is meant by first ionization energy? _______________________________________ _______________________________________________________________________ 2. Which element has the smallest first ionization energy? The largest? What are their values? ________________________________________________________________ 3. What generally happens to the first ionization energy of the elements within a period as the atomic number of the elements increases? ________________________________ 4. What accounts for the general trend in the first ionization energy of the elements within a period? ________________________________________________________________ ______________________________________________________________________ 5. Based on the graph, rank the group 2A elements in periods 1-5 in decreasing order of first ionization energy. _________________________________________________________ 8. What generally happens to the first ionization energy of the elements within a group as the atomic number of the elements increases? _____________________________________ -8- Periodic Table S1 9. What accounts for the general trend in the first ionization energy of the elements within a group? _________________________________________________________________ _______________________________________________________________________ b) Summary of trends in first ionization energies: trend down a GROUP: 3. trend across a PERIOD: Electronegativity = how much one atom pulls on another atom’s electrons in a bond only refers to atoms in a bond (molecule or compound) -9-