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The Periodic Table and Periodicity I. History of Development A. Antoine Lavoisier – French – late 1790s 1. Compiled list of 23 elements known at the time 2. changes in world a. electricity b. spectrometry c. industrial revolution B. Stanislao Cannizzaro - Italian – 1860 1. International Congress of Chemists in Germany 2. method for accurately measuring atomic mass C. John Newlands – English - 1864 1. Law of octaves –every 8th element had repeating pattern when arranged by increasing atomic mass 2. Did not work for all elements D. Lothar Meyer – German – 1869 E. Dmitri Mendeleev – Russian – 1869 1. organized 60+ known elements by atomic mass and other properties 2. 1871 - predicted properties of 3 unknown elements 3. By 1886 - Sc, Ga, Ge found with predicted properties -But, a few elements did not seem to fit in correct group F. Henry Mosely - 1911-1913 1. analyzed spectra of 38 metals to find nuclear charge (#p +) 2. rearranged periodic table by atomic number G. As other scientists found the existance of the noble gases & inner transition metals, they were added to PT Basic PT organization A. Main divisions 1. Metals a. transition metals b. inner transition metals c. lanthanide series d. actinide series 2. nonmetals 3. metalloids/semi-metals representative elements B. Group (family) names - vertical columns group # = # of valence e- except for transitions 1. alkali metals 2. alkaline earth metals 3. halogens 4. noble gases C. Periods - horizontal rows period# = # of principal energy levels Numbering system A and B 1-18 IV. Electron Configuration A. s-block elements 1. alkali metals 2. alkaline earth metals 3. filled/partially filled s orbitals B. p-block elements 1. filled/partially filled p orbitals 2. noble gases incredibly stable due to filled s & p orbitals C. d-block elements 1. filled outermost s and filled/partially filled nearby d orbitals D. f-block elements 1. lanthanide & actinide series 2. do not fill orbitals in a predictable manner 3. filled/partially filled outermost s and filled/partially filled 4f or 5f Example questions Without using the periodic table, determine the following: Determine the group, period, and block of the following e-config. [Ne]3s2 [He]2s2 [Kr]5s24d105p5 Write the e- config for the following elements: the group 2A element in the fourth period the noble gas in the fifth period the group 6A element in the second period 3. What are the symbols for the elements with the following valence e- configs? s2d1 s2p3 s2p6 Periodic Trends A. atomic radius 1. define: one-half the distance between adjacent nuclei 2. periodic trend: decreases as you go across a period due to increasing positive nuclear charge with no additional shielding effect 3. group trend: increases as you move down a group due to increasing principal energy levels with an increased shielding effect on the increased nuclear charge B. ionic radius define: radius of positive or negative ion positive ions: always smaller than neutral atom due to increased nuclear charge and empty outer orbital negative ions: always larger than neutral atom due to increased electrostatic repulsion 4. periodic trend: decreases as you move across a period group trend: increases as you move down a group C. ionization energy - 1st, 2nd, 3rd, etc 1. define: energy required to remove an electron from a gaseous atom (an indication of how strongly an atom holds onto its valence electrons 2. periodic trend: increase as you move across a period due to increased nuclear charge 3. group trend: decrease as you move down a group due to increased shielding effect and greater distance from nucleus D. Electronegativity define: relative ability of an atom to attract electrons in a chemical bond periodic trend: increases as you move across a period due to increased nuclear charge group trend: decrease (stay the same) as you move down a group due to increased shielding effect Electron Affinity define: energy change that occurs when an electrton is acquired by a neutral atom positive number: energy absorbed – leads to unstable nucleus – electron lost spontaneously negative number: energy released – leads to more stable nucleus – electron kept periodic trend: become increasingly negative as you move across a period (halogens are most EN)(Fluorine is most chemically active nonmetal) group trend: become increasingly positive as you move down a group due to increased shielding effect.
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