Chapter 6 Periodic Table Periodic Table

History A. John Newlands 1. Law of octaves 2. Properties repeat every 8 elements when arranged by atomic mass arranged by atomic mass B. Dmitri Mendeleev 1. Published 1 st periodic table 2. Arranged elements in order of increasing atomic mass atomic mass

Dobereiner’s Triads Name Atomic Mass Name Atomic Mass Name Atomic Mass Calcium 40 Barium 137 Average 88.5 Strontium 87.6 Chlorine 35.5 Iodine 127 Average 81.3 Bromine 79.9 Sulfur 32 Tellurium Average 79.8 Selenium 79.2 Johann Dobereiner ~1817 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 1 Li Na K John Newlands ~1863 Smoot, Price, Smith, Chemistry A Modern Course 1987, page Be Mg 3 B Al 4 C Si 5NP5NP 6OS6OS 7 F Cl

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 Henry G.J. Moseley Determined the atomic numbers of elements from their X -ray spectra (1914) Determined the atomic numbers of elements from their X -ray spectra (1914) Arranged elements by increasing atomic number Arranged elements by increasing atomic number Killed in WW I at age 28 Killed in WW I at age 28 (Battle of Gallipoli in Turkey)

E. Grouping of Elements Grouping of ElementsGrouping of Elements 1. Groups or families – elements in same vertical column have similar properties vertical column have similar properties 2. Periods – elements in the same horizontal row row 3. Representative elements – Groups designated with an A on periodic table – designated with an A on periodic table – wide range of properties wide range of properties properties 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 Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 367 N7N7 P 15 As 33 Sb 51 Bi 83 O8O8 S 16 Se 34 Te 52 Po 84 F9F9 Cl 17 Br 35 I 53 At 85 He 2 Ne 10 Ar 18 Kr 36 Xe 54 Rn 86 Li 3 Na 11 K 19 Rb 37 Cs 55 Fr 87 Be 4 Ca 20 Sr 38 Ba 56 Ra 88 Mg Alkali metals Alkaline earth metals Nitrogen family Oxygen family Halogens Noble gases

Classification of the Elements A. Organizing by electron configuration 1. Atoms in the same group have similar chemical properties because they have the chemical properties because they have the same number of valence electrons – same number of valence electrons – electron dot diagrams are the same electron dot diagrams are the same 2. Elements in the same period have valence electrons in the same energy level 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 because of increasing positive charge in nucleus nucleus 2. In a family, radius increases top to bottom because electrons are being added to higher because electrons are being added to higher energy levels and more electrons between valence energy levels and more electrons between valence electrons and nucleus result in “shielding effect” electrons and nucleus result in “shielding effect”

B. Ionic Radius 1. Positive ions are smaller than the neutral atoms atoms 2. Negative ions are larger than the neutral atoms atoms

C. Ionization Energy – the energy required to remove an outer electron from a gaseous atom Ionization Energy Ionization Energy 1. In a period, ionization energy generally increases left to right – nucleus has higher increases left to right – nucleus has higher positive charge and electrons are closer to positive charge and electrons are closer to nucleus nucleus 2. In a family, ionization energy decreases top to bottom because electrons are further to bottom because electrons are further from the nucleus and because of the shielding effect shielding effect

3. Octet rule – atoms tend to gain, lose or share electrons to acquire a full set of 8 share electrons to acquire a full set of 8 valence electrons valence electrons D. Electronegativity – the relative ability of an Electronegativity atom to attract electrons in a chemical bond 1. Increases in a period left to right 2. Decreases in a family top to bottom