Chemistry Chp. 4 Notes
Chemistry Chp. 4 Notes CHEM 1030-006
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This 4 page Class Notes was uploaded by Emma Karlson on Sunday October 11, 2015. The Class Notes belongs to CHEM 1030-006 at Auburn University taught by Brett A Cagg in Summer 2015. Since its upload, it has received 30 views. For similar materials see Fundamentals Chemistry 1 in Chemistry at Auburn University.
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Date Created: 10/11/15
Chemistry Chapter 4 41 Development of the Periodic Table 0 Law of octaves when the elements are arranged in order of atomic number that every eighth element that similar properties Mendeleev grouped elements according to properties 0 Ordering the periodic table by atomic number instead of atomic mass enabled scientists to make sense of discrepancies Entries today include atomic number and symbol and are arranged according to electron con guration Classi cation of Elements 0 The main group elements also called the representative elements are the elements in Groups 1A through 7A 0 The noble gases are found in Group SA and have completely lled p subshells 42 The Modern Periodic Table 0 The transition metals are found in Group 18 and BB through SB 0 Group ZB have lled d subshells and are not transition metals 0 The lanthanides and actinides make up the fblock transition elements 0 The outermost electrons of an atom are called the valence electrons o Involved in the formation of chemical bonds Similarity of valence electron con gurations helps predict chemical properties 43 Effective Nuclear Charge 0 Effective nuclear charge Ze is the actual magnitude of positive charge hat is experienced by an electron in the atom In a multielectron atom electrons are simultaneously attracted to the nucleus and repelled by one another 0 The results in shielding where an electron is partially shielded from the positive charge of the nucleus by the other electrons 0 Although all electrons shield one another to some extent the most effective are the core electrons 0 As a result the value of Ze increases steadily from left to right because the core electrons remain the same but Z increases Effective Nuclear Charge 0 In general the effective nuclear charge is given by Ze 20 0 Z is the nuclear charge the number of protons in the nucleus 0 039 is the shielding constant 0 Zeff increases from left to right across a period changes very little down a column 44 Periodic Trends in Properties of Elements 0 Atomic radius is the distance between the nucleus of an atom and its valence shell 0 Atomic radius in metals or metallic radius is half the distance between the nuclei of two adjacent identical metal atoms 0 Atomic radius in nonmetals or covalent radius is half the distance between adjacent identical nuclei connected by a chemical bond Atomic Radius 0 The atomic radius increases from top to bottom down a group 0 Increasing n so outermost shell lies farther from the nucleus 0 Atomic radius decreases from left to right across a period 0 Increasing Ze which draws the valence shell closer to the nucleus 0 Atomic radius decreases left to right across a period due to increased electrostatic attraction between the effective nuclear charge and the charge on the valence shell Ionization Energy 0 Ionization energy IE is the minimum energy required to remove an electron from an atom in the gas phase 0 The result is an ion a chemical species with a net charge 0 Nag gt Nag e39 o In general as Ze increases ionization energy also increases 0 Thus IE increases from left to right across a period 0 Within a given shell electrons with a higher value of L are higher in energy and thus easier to remove Removing a paired electron is easier because of the repulsive forces between two electrons in the same orbital It is possible to remove additional electrons in subsequent ionizations giving IE1 IE2 and so on o It takes more energy to remove the 2nd 3rd 4th etc electrons because it is harder to remove an electron from a cation than an atom It takes much more energy to remove core electrons than valence 0 Core electrons are closer to nucleus 0 Core electrons experience greater Ze because of fewer lled shells shielding them from the nucleus Electron Affinity 0 Electron affinity EA is the energy released when an atom in the gas phase accepts an electron CNQ e Cl g 0 Like ionization energy electron af nity increases from left to right across a period as Ze increases 0 Easier to add an electron as the positive charge of the nucleus increases 0 It s easier to add an electron to an s orbital than to add one to a p orbital with the same principal quantum number 0 Within a p subshell it s easier to add an electron to an empty orbital than to add one to an orbital that already contains an electron More than one electron may be added to an atom While many rst electron af nities are positive subsequent electron af nities are always negative 0 Considerable energy is required to overcome the repulsive forces between the electron and the negatively charged ion Metallic Character Metals tend to 0 Be shiny lustrous malleable and ductile 0 Be good conductors of both heat and electricity 0 Have low ionization energies commonly form cations Nonmetals tend to o Vary in color and are not shiny 0 Be brittle rather than malleable 0 Be poor conductors of both heat and electricity 0 Have high electron af nities commonly form anions o Metalloids are elements with properties intermediate between those of metals and nonmetals Coulomb s law F leQZd2 45 Electron Con gurations of Ions 0 To write the electron con guration of an ion formed by a main group element 0 1 Write the con guration for the atom o 2 Add or remove the appropriate number of electrons lons of Main Group Elements 0 Species with identical electron con gurations to the noble gas to the right are called isoelectronic Common monatomic ions arranged by their positions in the periodic table lons of dblock Elements 0 Removing electrons rst form the shell with the highest value of n forms ions of dblock elements 0 For Fe to Fe two electrons are lost from the 4s subshell not the 3d 46 lonic Radius o The ionic radius is the radius of a cation or an anion When an atom loses an electron to become a cation its radius decreases due in part to a reduction in electronelectron repulsions in the valence shell 0 A signi cant decrease in radius occurs when all of an atom s valence electrons are removed Comparing lonic Radius with Atomic Radius 0 When an atom gains one or more electrons and becomes an anion its radius increases due to increased electronelectron repulsion lsoelectronic Series 0 An isoelectronic series is a series of 2 or more species that have identical electron con gurations but different nuclear charges