Transcript Chapter 6
Chapter 6 Periodic Table Periodic Table • a chart that organizes information about the elements • knowing an elements location in the table allows you to predict properties • scientists have placed elements with similarities in the same groups on the table History: Joseph Dobereiner – Triads (1829) • made chart of groups of three elements that had similar properties • ex. Ca, Ba, Sr (found Sr mass is half way between the other two) Dobereiner’s Triads Triad 1 Triad 2 First element Calcium 40.1 Chlorine 35.3 Sulfur Third element Average Barium Iodine 126.9 Tellurium 88.7 81.2 Second Element Strontium 87.6 Bromine 137.3 Triad 3 32.1 127.6 79.9 79.9 Selenium 79.0 John Newlands – Law of Octaves (1863) • arranged in order of atomic mass • appeared to be a repetition of properties every eighth element • arranged elements into groups of 7 • Law of Octaves – same properties repeat every 8th element • (but it didn’t account for Noble gases and transition metals) Law of Octaves 1 2 3 Li Be B Na Mg Al K 4 C Si 5 N P 6 O S 7 F Cl Mendeleev’s Periodic Table 1869- Dmitri Mendeleev and Lothar Meyer both demonstrated a connection between atomic mass and properties -Mendeleev published his table first and better demonstrated its usefulness -placed elements with similar properties in vertical columns called groups or families -horizontal rows are periods -if no known element fits in a particular place, he left a blank (predicted the properties of it for someone to discover later) Mendeleev’s Prediction Ekasilicon (Es) (predicted properties) • Atomic Mass: 72 • High Melting Point • Density: 5.5 g/ml • Dark gray metal • Will obtain from K2EsF6 • Slightly dissolved by HCl • Will form EsO2 • Density of EsO2: 4.7 g/ml Germanium (Ge) (1886) (actual properties) • Atomic Mass: 72.61 • Melting Point: 945° C • Density: 5.323 g/ml • gray metal • Will obtain from K2GeF6 • Not dissolved by HCl • Will form GeO2 • Density of GeO2:4.7 g/ml Mendeleev’s Periodic Law • physical and chemical properties of elements were periodic functions of their atomic mass • by arranging by atomic mass he did find he had some elements in groups with different properties (ex. Te and I, Co and Ni) Modern Periodic Table -Henri Moseley’s discovery of the atomic number corrected Mendeleev’s problems and led to the modern table Modern Periodic Law • properties of elements are periodic functions of their Atomic numbers • found atoms of similar electron configurations found in similar groups • The Development of the Periodic Table Chinese Periodic Table German Table (Periodensystem der Elemente ) Russian Norwegian • http://no.wikipedia.org/wiki/Periodesystem et_i_stor_utgave • Romanian Parts of the Periodic Table Groups or Families - vertical column of elements w/ similar properties Group 1- Alkali Metals Group 2 – Alkaline Earth Metals Group 16- Chalcogens Group 17 – Halogens Group 18 – Noble or Inert gases 3-12 – Transition metals Staircase- metalloids Bottom rows- Rare earth metals (Lanthanoids & Actinoids or Lathanides & Actinides) Periods - horizontal rows (of elements w/ common outer energy level) Properties of Elements Metals: -left side of staircase -hard, shiny, conduct heat or electricity well, malleable, ductile -have 3 or fewer electrons in outer level (3 or less dots in dot diagram) Nonmetals -right side of staircase -gases or brittle solids, dull surfaces, used as insulators -have 5 or more electrons in outer energy level Metalloids -have properties of both metals and non metals -found on staircase Reading the Periodic Table Organizing elements by electron configuration • Atoms in same group have similar chemical properties because they have similar electron configurations and similar # of valence electrons • Period numbers tell us the outer most energy levels • The periodic table not only has rows & columns but sections or blocks representing the sublevels Outer energy levels 1 2 3 4 5 sblock pblock d - block 6 7 f -block • The energy level number in front of (s) is always the period number • The energy level number in front of the (p) is the period number • The energy level number in front of the (d) is one less than the period number • The energy level number in front of the (f) is 2 less than the period number Periodic Trends • Properties of elements change in predictable ways depending on their location on the periodic table because of their electron configuration Atomic Radius -half the distance between adjacent nuclei in two atoms of the element bonded together Trends: Ionic Radius • when elements lose or gain electrons to form ions their size increase and decreases • an atom that loses electrons and becomes positively charged gets smaller • an atom that gains electrons and becomes negatively charged gets larger Trends: Positive ions decrease Generally decreases Negative ions decrease Ionization Energy -energy required to remove an electron from a gaseous atom Trends: Electronegativity • the relative ability of the atoms to attract electrons in a chemical bond Electronegativity Trends: