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Dmitri Mendeleev …arranged elements in order of their atomic numbers, such that elements with similar properties fell into the same column or group. Periodicity and the Periodic Table the result… The Periodic Table Periods Horizontal Rows Groups Metals vs. Non-Metals Vertical Columns Nonmetals Metals “Metalloids” (Semi-conductors) 1 Metals: Non-metals Good conductors of heat and electricity Malleable, Ductile, Shiney Nonconductors (insulators) Dull, Brittle Family: The Alkali Metals Families of Elements Elements grouped together by similar properties Group 1: Li, Na, K, Rb, Cs, Fr. Highly Reactive All have only 1 valence electron in s orbital Alkali Metals Alkaline Earth Metals Transition Metals Semi-Conductors Halogens Noble Gases Other Non-Metals Form +1 cations Family: The Alkaline Earth Metals Family: The Transition Metals Group 2: Be, Mg, Ca, Sr, Ba, Ra. Groups 3 through 12 Somewhat Reactive Generally less reactive than groups 1 and 2 All have 2 valence electrons in s orbital d-orbital filling region of the table Form +2 cations *everything else in the periodic table is often referred to as the Main Group Elements 2 “Sub-Family”: The Lanthanide and Actinide Series Part of the transition metals f-orbital filling region of table Also called “Rare Earth Metals” All actinides are radioactive Family: The “Metalloids” (Semi-Conductors) Intermediate conductors of heat and electricity Silicon is used for computer chips because of its conductive properties Family: The Halogens Group 17: F, Cl, Br, I, At Highly Reactive All have 7 valence electrons Form -1 anions Family: The Noble Gases Group 18: He, Ne, Ar, Kr, Xe, Rn. Family: The Other Non-Metals The 6 leftover elements: Least Reactive Elements (most stable) C, N, O, P, S, Se O, S, Se, form –2 anions All have full valence shell N, P, form –3 anions C generally does not form ions Do not form ions 3 Family: The Other Metals The 8 leftover metals: Al, Ga, In, Sn, Tl, Pb, Bi, Po Form the same ions as the other elements in their group. Special Case: Hydrogen Hydrogen is in a class of its own… it does not belong to any other family. Often, Hydrogen occurs as a H+ ion, which is really is just a proton! Periodic Law “the physical and chemical properties of elements are periodic functions of their atomic number” for example… Electronegativity Ionization Energy Density Atomic Radius all of these properties exhibit Periodic Trends 4 Electronegativity Electronegativity = “electron hogging” = the tendency of an atom to attract electrons “Electron Hogging” Electronegativity Ionization Energy = the amount of energy needed to remove an electron from an atom. So it is like “cationization” energy In general, electronegativity values increase across a period and decrease down a group. Ionization Energy Sodium (Z=11) tends to lose its one Ionization Energy e-. It has a low ionization energy… …because little energy is needed to remove the electron. Fluorine (Z=9) tends to gain one e-. It has a very high ionization energy… …because a massive amount of energy would be needed to remove an electron! A high ionization energy… …means the atom does not lose electrons easily A low ionization energy… …means the atom loses electrons easily 5 Ionization Energy Ionization Energy 1st ionization energy = amount of energy needed to remove the first electron from an atom. 2nd ionization energy = amount of energy needed to remove a second electron from an atom. etc.. Atomic Radius = electrons in unbonded atoms are constantly moving, so it is difficult to measure the radius or diameter of a single atom… In general, ionization energies increase across a period and decrease down the groups. Atomic Radius ??? so, we look at bonded atoms… Atomic Radius = one half the distance between the nuclei of 2 identical atoms that are bonded together Usually measured in angstroms (Å) or picometers (pm) 1 angstrom (Å) = 10–10 meters 1 picometer (pm) = 10–12 meters Density mass … depends on the number of protons and neutrons. In general, atomic radii decrease across a period and increase down a group. = mass ÷ volume volume … depends on the electron configuration. so,a complex pattern emerges … 6 Periodic Table You must memorize the following 45 element names and symbols. I suggest you make some flash cards. A Review; Classification of Elements 7 8 9