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Periodic Table notes.notebook February 08, 2016 History of the Periodic Table Early Classification Mendeleev’s Periodic Table: (1869) Arranged elements in a table by atomic mass. Elements with similar properties were grouped in columns. Mendeleev left empty spaces for elements that were “undiscovered”. He used his table to predict the properties of these elements (Sc, Ga, Ge) and he was right! Why did some elements (Ar & K, Co & Ni, I & Te) not follow the atomic mass pattern? Why were the properties periodic? Feb 88:53 AM The Modern Periodic Table Moseley’s Atomic Number: (1911) led to the arrangement of the periodic table by increasing atomic number; retained columns with similar properties Modern Periodic Law: The properties of the elements are periodic functions of their atomic numbers Feb 88:56 AM Periodic Table notes.notebook February 08, 2016 Arrangement of the Modern Periodic Table Physical Property: a characteristic of a substance that can be observed or measured without changing the identity of the substance Chemical Property: a description of a substance’s ability to react (or not react). Changes into a new substance as a result of the observation or measurement. Feb 88:56 AM General Properties of the Elements Metals: left of the staircase and Al Good conductors of heat and electricity, malleable, ductile, shiny, high melting points, mostly solids (Hg is the exception), few valence e‐ Nonmetals: right of the staircase and H Poor conductors of heat and electricity, are gases or dull, brittle solids, low melting points, 5‐7 valence e‐ Metalloids (semimetals): touching the staircase except Al Solids, have some properties of metals and nonmetals, semiconductors Feb 88:56 AM Periodic Table notes.notebook February 08, 2016 Families or Groups (columns) Main Group Elements (s & p blocks) Alkali Metals – Group I most reactive metals, not found free in nature, silvery, soft, react vigorously with H2O, lose e‐ in reactions, general valence structure ns1, general dot diagram  Alkaline Earth Metals – Group 2 reactive, not found free in nature, harder, denser, stronger than Group I, lose e‐ in reactions, general valence structure ns2, general dot diagram  Halogens – Group 17 most reactive nonmetals, “salt formers”, gases (F, Cl), liquid (Br), solids (I, At), gain e‐ in reactions, general valence structure ns2np5, general dot diagram Noble Gases – Group 18 stable, unreactive elements (although some can form compounds), discovered between 1894‐1900, general valence structure ns2np6, general dot diagram, He is the exception Feb 88:58 AM Transition elements (d block) – metallic properties, less reactive, harder & stronger than s‐block, sum of the outer “s” and “d” electrons gives the group number, variable oxidation numbers (charges), often form colored ions, deviation in e‐ configurations Inner Transition Elements or Rare Earth Elements (f block) Lanthanides (early 1900’s): atomic numbers 58‐71 – shiny metals, reactivity similar to Group 2 Actinides: atomic numbers 90‐103 – all are radioactive, Th through Np are naturally occurring, all the rest are synthetic Hydrogen: unique properties! Physical properties of a gas, chemical properties of a Group I metal Feb 89:00 AM Periodic Table notes.notebook February 08, 2016 Periodic Properties of the Elements: A result of Zeff and shielding by core electrons Valence e‐ (outermost energy level, s & p e‐) Group 1 2 3‐12 13 14 15 16 17 18 e‐ config s1 s2 s2d1‐10 s2p1 s2p2 s2p3 s2p4 s2p5 s2p6 number of valence e‐ 2 1,2 ‘d’ e‐ can be lost 3 4 5 6 7 8 varies (all +) +3 ±4 ‐3 ‐2 ‐1 0 1 oxidation +1 number varies +2 (except He) Remember: lose e‐ (+); gain e‐ (‐)! Feb 89:01 AM Atomic Radius: ½ the distance between nuclei of identical atoms bonded together. Across a Period: the atomic radius decreases due to nuclear charge increase (e‐ cloud pulled in tighter to nucleus due to increased attractive force) Down a Group: the atomic radius increases due to increase in the number of energy levels Feb 89:03 AM Periodic Table notes.notebook February 08, 2016 Ionic Radius Cation (+ ion, more p+ than e‐): ionic radius is less than atomic radius Anion (‐ ion, less p+ than e‐): ionic radius is greater than atomic radius Across a row: ionic radius goes down due to increasing nuclear charge. As the first anion in the period is formed, the ionic radius jumps up, then goes down again as nuclear charge increases. Down a Group: the ionic radius increases due to increase in the number of energy levels Feb 89:04 AM Reactivity Metals: the most reactive is Fr (largest, easiest to lose e‐) Metallic Behavior decreases as move across a period, increases as move down a group Nonmetals: the most active is F (smallest, hardest to lose e‐) Nonmetallic Behavior increases as move across a period, decreases as move down a group Feb 89:04 AM Periodic Table notes.notebook February 08, 2016 Ionization Energy (IE): the energy needed to remove one e‐ from the valence shell of a neutral atom, often called 1st ionization energy, measured in kJ/mol Across a Period: ionization energy increases due to nuclear charge increase, atomic radius decrease, sublevel deviations. Metals typically have a low IE, nonmetals typically have a high IE. Down a Group: ionization energy decreases due to increasing energy level (distance from the nucleus), increasing atomic radius, shielding IE increases as each successive e‐ is removed: 3rd IE > 2nd IE > 1st IE; harder to remove an e‐ from a more (+) ion Feb 89:04 AM Electronegativity: a measure of the ability of an atom in a compound to attract e‐ follows same trends as IE Electron Affinity: the attraction a nonbonded atom has for an additional e‐ follows same trends as IE Feb 89:04 AM Periodic Table notes.notebook February 08, 2016 Summarizing Periodic Trends Feb 89:05 AM Factors Affecting Periodic Properties Nuclear Charge (Zeff): affects pull on e‐ cloud; more p+, more pull (calculated by Protons minus CORE electrons) Atomic Size: number of energy levels affects the distance between nucleus and valence e‐; more energy levels, more distance Shielding: the number of e‐ between the nucleus and valence e‐, affects the pull by the nucleus; more e‐, more shielding, easier to remove valence e‐ Sublevel Stability: ½ and full sublevels are more stable than other configurations Feb 89:08 AM