The Periodic Table. Reading: Shriver 7 Atkins,

Transcription

1 Lecture 5 The Periodic Table Reading: Shriver 7 Atkins,

2 The classification of the elements Metals Typically lustrous, malleable, ductile, electrically conducting solids at room temperature t (Na, Al, Cu, Fe) Non- Metals Often gases (oxygen, chlorine), liquids (bromine), or solids (sulfur) that do not conduct electricity it appreciably Metalloids Solids with properties intermediate of metals and nonmetals (i.e., semiconductors): Si, Ge, As, Te In general 1. Metals combine with nonmetals to give hard, non-volatile solids 2. Nonmetals combine with each other to form volatile molecular compounds 3. Metals combine with metals to give alloys

3 The Periodic Table Layout reflects electronic structure: block: subshell occupied period (or row): principle quantum number n group (or column): related to number of electrons in valence shell

4 S-Block Except for H and He, electrons are easily lost for form positive ions He is exceedingly stable and has no known stable compounds All other s-block elements are very powerful reducing agents never occur naturally in the free state The metallic forms of these elements can only be extracted by electrolysis of a molten salt (Sir Humphry Davy) All are fire hazards and show be stored in Ar Generally react vigorously with H 2 O to liberate hydrogen

5 Halogens: part of the p-block Highly reactive: found in the environment only as compounds or ions Only periodic table group that contains elements in all 3 states of matter: F and Cl: gases, Br: liquid; Iodine and Astatine, solids F is one of the most reactive elements, attacking otherwise inter materials like glass and forming compounds with the heavier noble gases. Once is does react, the resulting molecule is very inert. Teflon: F+C Hydrogen halides form a series of very strong acids

6 Noble Gases: part of the p-block Odorless Odorless, colorless, monatomic gases Non-flammable, Low chemical reactivity: Ne < He < Ar< Kr < Xe< Rn First noble gas compounds: XeF 4 and XeF 2 (used to etch Si)

7 d-block Co Cr Ni Cu Mn Partly filled d-shell results in unique qualities: 1 Formation of compounds and complexes whose color is due to 1. Formation of compounds and complexes whose color is due to d-d transitions 2. Formation of compounds in many oxidation states, due to low reactivity of unpaired d-electrons 3. Formation of many paramagnetic compounds

8 F-block: Lanthanoids Term rare earth refers to hiding behind each other in minearls First discovered lanthanoid, Lanthanum, was found in a cerium mineral All contain 4f-shell electrons, except Lanthanum (which is a d-block element) All form trivalent cations: Ln 3+ All Lanthanoid ions are fluorescent, as a result of the forbidden nature of f-f transitions

9 f-block: Not as rare as you think Rare earths: Rare earths: Ce is 26 th most abundant element

10 Applications of Lanthanoids Europium-doped Yttrium vanadate was the first red phosphor to enable the development of color tv screens Lanthanoids deflect UV and IR radiation: used in production of sunglass lenses Lasers, fiber amplifiers, transmission links for internet Amplification & upconversion rticle/tech/41882 First color tv broadcast in 1953 From WebMD: Erbium laser resurfacing is designed to remove superficial and moderately deep lines and wrinkles on the face hands, neck, or chest.

11 f-block: Actinoids All are man-made, except for thorium and uranium All are radioactive First synthesized as part of the Manhattan project in 1944 Some have electrons in 6d orbitals, but in compounds the 6s electrons and any d electrons are lost, leaving the ions with an electronic configuration [Rn]5fn Need particle colliders, nuclear reactors, or supernova for their synthesis A pellet of 238PuO 2 to be used in a radioisotope thermoelectric generator for either the Cassini or Galileo mission. The pellet produces 62 watts of heat and glows because of the heat generated by the radioactive decay (primarily α). Photo is taken after insulating the pellet under a graphite blanket for minutes and removing the blanket. (from Wikipedia)

12 Trend 1: Effective Nuclear Charge The net positive charge experienced by an electron in a multielectron atom (shielding prevents outermost electrons from feeling full nuclear charge) ctive nuclear charge Effec Effective nuclear charge

13 Trend 1: Effective Nuclear Charge

14 Trend 2: Atomic Radius The distance from the nucleus to the outermost stable electron orbital (here in pm). Increases down a group due to addition of a new energy shell. Decreases across a period because effective nuclear charge increases, attracting electrons

15 Trend 2: Atomic Radius The distance from the nucleus to the outermost stable electron orbital (here in pm). Increases down a group due to addition of a new energy shell. Decreases across a period because effective nuclear charge increases, attracting electrons

16 Trend 3: Ionization Energy (IE) The minimum energy required to remove one electron from each atom in a mole of atoms in the gaseous state. A(g) A + (g)+e - (g) IE=E(A +, g)-e(a, g)

17 Trend 4: Electron affinity (EA) Electron affinity: the energy change when a gas-phase atom gains an electron A(g) +e - (g) A - (g) EA=E(A,g)-E(A -,g)

18 Trend 5: Absolute electronegativity Electronegativity: the ability of an atom to attract electrons when it is part of a compound (IE EA) 2 Y e Y H IE Y e Y Y 2 e - Y - H EA H (IE EA) Electronegativity: A measure of the attraction of Y + for an electron pair, or alternatively, the average of the attraction of Y + and Y for an electron

19 Trend 5: Absolute electronegativity Electronegativity: the ability of an atom to attract electrons when it is part of a compound increases across a period, decreases down a group

20 Trend 6: Absolute hardness Hardness: corresponds to the energy involved in the disproportionation reaction of Y: Y ½ Y + + ½ Y - (IE EA) 2 A measure of how easy it is to polarize the electron cloud of Y. Polarizability: Ability of an atom to be distorted by an electric field Polarizability is high if the separation of frontier orbitals is small Large, highly charged anions are easily polarized Cations that do not have noble-gas configurations are easily polarized

21 Electronegativity & Polarizability Interpretation of the electronegativity y and polarizability in terms of the energies of the frontier orbitals (the highest filled and lowest unfilled atomic orbitals) a) Relatively low electronegativity and polarizability b) Relatively high electronegativity and polarizability

22 Trend 7: Metallic character of the elements

23 Trend Summary Metallic character Ionization energy Ato omic radius Effective nuclear cha arge Electron affinity & electronegativity Ioni ization ene ergy Effective nuclear charge Atomic radius