Transcript Chapter 6
Chapter 6 Periodic Table History A. John Newlands 1. Law of octaves 2. Properties repeat every 8 elements when arranged by atomic mass B. Dmitri Mendeleev 1. Published 1st periodic table 2. Arranged elements in order of increasing atomic mass Dobereiner’s Triads Johann Dobereiner ~1817 Name Atomic Mass Name Atomic Mass Name Atomic Mass Calcium Barium 40 137 Chlorine Iodine 35.5 127 Sulfur Tellurium 32 127.5 Average 88.5 Average 81.3 Average 79.8 Strontium 87.6 Bromine 79.9 Selenium 79.2 Dobereiner discovered groups of three related elements which he termed a triad. Smoot, Price, Smith, Chemistry A Modern Course 1987, page 161 Newland’s Law of Octaves John Newlands ~1863 Newland’s Law of Octaves 1 2 3 4 5 6 7 Li Na K Be Mg B Al C Si N P O S F Cl Smoot, Price, Smith, Chemistry A Modern Course 1987, page 161 C. Henry Mosley – arranged elements in order of increasing atomic number – modern periodic table D. Periodic Law – the properties of the elements are a periodic function of the atomic number Modern Periodic Table Henry G.J. Moseley Determined the atomic numbers of elements from their X-ray spectra (1914) Arranged elements by increasing atomic number Killed in WW I at age 28 (Battle of Gallipoli in Turkey) 1887 - 1915 E. Grouping of Elements 1. Groups or families – elements in same vertical column have similar properties 2. Periods – elements in the same horizontal row 3. Representative elements – Groups designated with an A on periodic table – wide range of properties 4. Transition elements Group designated with a B 5. Metals – elements to the left of the heavy stairstep line 6. Nonmetals – elements to the right of the heavy stairstep line 7. Metalloids – elements adjacent to the heavy stairstep line except for aluminum which is a metal 8. Alkali metals – group 1A 9. Alkaline earth metals – group 2A 10. Noble gases – group 8A 11. Halogens – group 7A Groups of Elements 1 18 He 2 13 14 15 16 17 2 Li Be N O F Ne 3 4 7 8 9 10 Na Mg P S Cl Ar 11 12 15 16 17 18 K Ca As Se Br Kr 19 20 33 34 35 36 Rb Sr Sb Te I Xe 37 38 51 52 53 54 Cs Ba Bi Po At Rn 55 56 83 84 85 86 Fr Ra 87 88 1 Alkali metals 16 Oxygen family 2 Alkaline earth metals 17 Halogens 18 Noble gases 15 Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 367 Nitrogen family Classification of the Elements A. Organizing by electron configuration 1. Atoms in the same group have similar chemical properties because they have the same number of valence electrons – electron dot diagrams are the same 2. Elements in the same period have valence electrons in the same energy level B. s,p,d,f Blocks – indicates sublevel to which electrons are being added Periodic Trends A. Atomic Radius 1. In a period radius decreases left to right because of increasing positive charge in nucleus 2. In a family, radius increases top to bottom because electrons are being added to higher energy levels and more electrons between valence electrons and nucleus result in “shielding effect” B. Ionic Radius 1. Positive ions are smaller than the neutral atoms 2. Negative ions are larger than the neutral atoms C. Ionization Energy – the energy required to remove an outer electron from a gaseous atom 1. In a period, ionization energy generally increases left to right – nucleus has higher positive charge and electrons are closer to nucleus 2. In a family, ionization energy decreases top to bottom because electrons are further from the nucleus and because of the shielding effect 3. Octet rule – atoms tend to gain, lose or share electrons to acquire a full set of 8 valence electrons D. Electronegativity – the relative ability of an atom to attract electrons in a chemical bond 1. Increases in a period left to right 2. Decreases in a family top to bottom