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Periodic Table Larry Scheffler Lincoln High School The Periodic Table-Key Questions What is the periodic table ? What information is obtained from the table ? How can elemental properties be predicted based on the Periodic Table? Periodic Table • The development of the periodic table brought a system of order to what was otherwise an collection of thousands of pieces of information • The periodic table is a milestone in the development of modern chemistry. It not only brought order to the elements but it also enabled scientists to predict the existence of yet undiscovered elements. Early Attempts to Classify Elements Dobreiner’s Triads (1827) • Classified elements in sets of three having similar properties. • Found that the properties of the middle element were approximately an average of the other two elements in the triad. Dobreiner’s Triads Element Atomic Mass Cl Br I Ca Sr Ba 35.5 79.9 126.9 40.1 87.6 137.3 Average Density 81.2 88.7 1.56 3.12 4.95 1.55 2.6 3.5 Average 3.25 2.53 Note: In each case, the numerical values for the atomic mass and density of the middle element are close to the averages of the other two elements Newland’s Octaves -1863 John Newland attempted to classify the then 62 known elements of his day. He observed that when classified according to atomic mass, similar properties appeared to repeat for about every eighth element His Attempt to correlate the properties of elements with musical scales subjected him to ridicule. In the end his work was acknowledged and he was vindicated with the award of the Davy Medal in 1887 for his work. Dmitri Mendeleev Dmitri Mendeleev is credited with creating the modern periodic table of the elements. He gets the credit because he not only arranged the atoms, but he made predictions based on his arrangement which were shown to be quite accurate. Mendeleev’s Periodic Table • Mendeleev organized all of the elements into one comprehensive table. • Elements were arranged in order of increasing mass. • Elements with similar properties were placed in the same row. Mendeleev’s Periodic Table Mendeleev’s Periodic Table Mendeleev left some blank spaces in his periodic table. At the time the elements gallium and germanium were not known. He predicted their discovery and estimated their properties Periodic Table The Periodic Table has undergone several modifications before it evolved in its present form. The current form is usually attributed to Glenn Seaborg in 1945 Periodic Table Expanded View The Periodic Table can be arranged by energy sub levels The s-block is Group IA and & IIA, the p-block is Group IIIA - VIIIA. The d-block is the transition metals, and the f-block are the Lanthanides and Actinide metals The way the periodic table usually shown is a compressed view. The Lanthanides and actinides (F block)are cut out and placed at the bottom of the table. Periodic Table: Metallic Arrangement Layout of the Periodic Table: Metals vs. nonmetals 1 IA 1 18 VIIIA 2 IIA 13 IIIA 14 IVA 15 VA 16 VIA 17 VIIA 2 3 4 5 6 7 3 IIIB 4 IVB 5 VB 6 VIB 7 VIIB 8 9 VIIIB Metals 10 11 IB 12 IIB Nonmetals The Three Broad Classes Are Main, Transition, Rare Earth Main (Representative), Transition metals, lanthanides and actinides (rare earth) Reading the Periodic Table: Classification Nonmetals, Metals, Metalloids, Noble gases Periodic Table: The electron configurations are inherent in the periodic table 1 IA 1 2 3 4 5 6 7 H 1s1 18 VIIIA 2 IIA Li Be 2s1 2s2 Na Mg 3s1 3s2 13 IIIA B 2p1 3 IIIB 4 IVB Sc 3d1 Rb 5s1 Ca 4s2 Sr 5s2 Y 4d1 V Ti Cr Mn Fe Co 3d2 3d3 4s13d5 3d5 3d6 3d7 Zr Nb Mo Tc Ru Rh 4d2 4d3 5s14d5 4d5 4d6 4d7 Cs 6s1 Ba 6s2 La 5d1 Hf Ta W Re Os 5d2 5d3 6s15d5 5d5 5d6 Fr 7s1 Ra 7s2 Ac Rf 6d1 6d2 K 4s1 5 VB 6 VIB 7 VIIB Db Sg Bh 6d3 7s16d5 6d5 8 9 VIIIB 14 IVA 15 VA 16 VIA 17 VIIA B 1 2p C N O 2 3 2p 2p 2p4 F 2p5 Ne 2p6 Cl 3p5 Ar 3p6 He 1s2 10 11 IB 12 IIB Ni 3d8 Cu 4s13d10 Ni 4d8 5s14d10 Zn Ga Ge 3d10 4p1 4p2 Cd In Sn 10 4d 5p1 5p2 As Se Be 4p3 4p4 4p5 I Sb Te 5p3 5p4 5p5 Kr 4p6 Xe 5p6 Hg Tl Pb 5d10 6p1 6p2 Bi Po At 6p3 6p4 6p5 Rn 6p6 Ir Ni 7 5d 5d8 Hs Mt 6d6 6d7 Ag Au 6s15d10 Al Si 3p1 3p2 S P 3 3p 3p4 Periodic Table Organization-----Groups or Families Vertical columns in the periodic table are known as groups or families The elements in a group have similar electron configurations Periodic Table Organization ---- Periods Horizontal Rows in the periodic table are known as Periods The Elements in a period undergo a gradual change in properties as one proceeds from left to right Periodic Properties Elements show gradual changes in certain physical properties as one moves across a period or down a group in the periodic table. These properties repeat after certain intervals. In other words they are PERIODIC Periodic properties include: -- Ionization Energy -- Electronegativity -- Electron Affinity -- Atomic Radius -- Ionic Radius Trends in Ionization Energy Ionization energy is the energy required to Remove an electron from an atom Ionization energy increases across a period because the positive charge increases. Metals lose electrons more easily than nonmetals. Nonmetals lose electrons with difficulty (they like to GAIN electrons). Trends in Ionization Energy The ionization energy increases UP a group Atoms near the top of a group are effected less by the Shielding Effect. Ionization Energies Ionization Energies are Periodic Electronegativity Electronegativity is a measure of the ability of an atom in a molecule to attract electrons to itself. This concept was first proposed by Linus Pauling (1901-1994). He later won the Nobel Prize for his efforts Periodic Trends: Electronegativity In a group: Atoms with fewer energy levels can attract electrons better (less shielding). So, electronegativity increases UP a group of elements. In a period: More protons, while the energy levels are the same, means atoms can better attract electrons. So, electronegativity increases RIGHT in a period of elements. Trends in Electronegativity Electronegativity Electronegativity The Electron Shielding Effect Electrons between the nucleus and the valence electrons repel each other making the atom larger. Atomic Radius The radius increases down a group. Because electrons are added further from the nucleus, there is less attraction. This is due to additional energy levels and the shielding effect. Each additional energy level “shields” the electrons from being pulled in toward the nucleus. The radius decreases on going across a period. Atomic Radius The radius decreases across a period owing to increase in the positive charge from the protons. Each added electron feels a greater and greater + charge because the protons are pulling in the same direction, where the electrons are scattered. Large Small Core Charge The concept of core charge can be used to better understand trends in atomic radii. Core charge = nuclear charge (ie: number of protons) – number of inner-shell electrons. Eg: Na (s) 11p – 10e = +1 Core Charge The greater the core charge, the greater the attraction of protons to electrons. greater core charge means SMALLER atomic radii. Core charge increases across period 3 so atomic radii decreases. Atomic Radius Atomic Radius Trends in Ion Sizes Radius in pm Cations Cations (positive ions) are smaller than their corresponding atoms Ion Sizes Does the size go up or down when gaining an electron to form an anion? Ionic Radius + Li,152 pm 3e and 3p Li + , 78 pm 2e and 3 p Forming a cation. CATIONS are SMALLER than the atoms from which they come. The electron/proton attraction has gone UP (increased core charge) and so the radius DECREASES. Ionic Radius for Cations Positve ions or cations are smaller than the corresponding atoms. Cations like atoms increase as one moves from top to bottom in a group. Anions Anions (negative ions) are larger than their corresponding atoms Ionic Radius-Anions F 64 pm 9e- and 9p+ F- , 133 pm 10 e- and 9 p+ Forming an anion. ANIONS are LARGER than the atoms from which they come. The electron/proton attraction has gone DOWN (core charge decreases) and so size INCREASES. Trends in ion sizes are the same as atom sizes. Ionic Radii for Anions Negative ions or anions are larger than the corresponding atoms. Anions like atoms increase as one moves from top to bottom in a group. Ionic Radius for an Isoelectronic Group Isoelectronic ions have the same number of electrons. The more negative an ion is the larger it is and vice versa. Summary of Periodic Trends Properties of the Third Period Oxides Properties of the Third Period Chlorides The Periodic Table--Summary The periodic table is a classification system. Although we are most familiar with the periodic table that Seaborg proposed more than 60 years ago, several alternate designs have been proposed. Alternate Periodic Tables Alternate Periodic Tables II