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CHAPTER 6 CHEMICAL PERIODICITY DEVELOPMENT OF THE PERIODIC TABLE • • Scientists needed a way to organize and refer to the growing number of known elements Categorized the elements according to similarities in their physical and chemical properties (Dobereiner’s Triads, Mendeleev’s and Newland’s Periodic Tables) • Relationship between atomic structure and properties of elements (Moseley’s Periodic Table) MENDELEEV’S PERIODIC TABLE • • • Mendeleev listed the elements in horizontal rows in order of increasing atomic mass Regular patterns of physical and chemical properties occurred in vertical columns Blank spaces left where unknown elements belonged, but able to predict their properties MOSELEY’S PERIODIC TABLE • • Moseley determined atomic number of the atoms of the elements Arranged the elements by order of atomic number, not by atomic mass MODERN PERIODIC TABLE • The horizontal rows of the periodic table are called periods (organized by increasing atomic number) • The vertical columns are called groups or families (organized by chemical properties) • Periodic Law: when the elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties ORGANIZATION OF THE PERIODIC TABLE Group Period METALS, METALLOIDS, AND NONMETALS Metalloids MAIN GROUP OR REPRESENTATIVE ELEMENTS IA IIA VIII A IIIA IVA VA VIA VIIA p-block s-block TRANSITION ELEMENTS IIIB IVB VB VIB VIIB VIIIB d-block f-block (inner transition elements) IB IIB SPECIAL GROUPS WITHIN THE PERIODIC TABLE ELECTRON CONFIGURATIONS AND PERIODICITY • • Electron plays the greatest part in determining the physical and chemical properties of an element Elements can be classified into four different categories based on their electron configurations ELECTRON CONFIGURATIONS AND PERIODICITY 1. The noble gases are elements in which the outermost s and p sublevels are filled Called inert gases because they do not partake in chemical reactions • Valence: outermost s and p orbitals • Octet: 8 electrons in valence shell 2. The representative elements are elements whose outermost s or p sublevels are only partially filled (group A) • Alkali metals: group 1A elements • Alkaline earth metals: groups 2A elements • Halogens: nonmetallic elements of group 7A • Group number = number of valence electrons ELECTRON CONFIGURATIONS AND PERIODICITY 2. The representative elements are elements whose outermost s or p sublevels are only partially filled (group A) • Alkali metals: group 1A elements • Alkaline earth metals: groups 2A elements • Halogens: nonmetallic elements of group 7A • Group number = number of valence electrons ELECTRON CONFIGURATIONS AND PERIODICITY 3. The transition metals are elements whose outermost s sublevel and the nearby d sublevel contain electrons (group B) 3. The inner transition metals are elements whose outermost s sublevel and the nearby f sublevel contain electrons ELECTRON CONFIGURATIONS AND PERIODICITY • • • • • S block: groups 1A and 2A and He P block: groups 3A, 4A, 5A, 6A, 7A, and 8A except He D block: transition metals F block: inner transition metals Period number corresponds to the principal energy level for the S and P blocks only PERIODIC TRENDS IN ATOMIC SIZE • The radius of atoms: atomic radii • From one group to the next, atomic radius decreases because the electrostatic attraction between increasingly larger nuclei increases, pulling the electrons closer to the nucleus • From one row to the next, atomic radius increases because increasing numbers of neutrons shield the electrostatic force and valence electrons are located further and further away from the nucleus PERIODIC TRENDS IN IONIC SIZE • Ionic radii is the size of an ion compared to same neutral atom • Cations (positive ions) are smaller because of the reduced energy level with the same number of protons • Anions (negative ions) are larger because of a reduced effective nuclear charge on outer electrons • From one row to the next, atomic radius increases because increasing numbers of neutrons shield the electrostatic force and valence electrons are located further and further away from the nucleus PERIODIC TRENDS IN IONIZATION ENERGY • • • The energy that is required to overcome the attraction of the nuclear charge and remove an electron to create a positive atom is the ionization energy Increased nuclear charge that occurs from one group to the next accounts for electrons being held more tightly within the atom. The more tightly they are held, the greater the amount of energy that is required to remove and electron from an atom From one row to the next, ionization energy increases because increasing numbers of neutrons shield the electrostatic force and valence electrons are located further and further away from the nucleus PERIODIC TRENDS IN ELECTRONEGATIVITY • • The electronegativity of an element is the ability of an atom to attract electrons within a bond Electronegativity increases as you go across a period form left to right and decreases as you move down a group