Week 3 Atoms and the Periodic Table.pdf

Chapter 2 Week 3 Atoms and the Periodic Table Chapter Outline History of the Periodic Table The Modern Periodic Table Periodic Trends  History of Periodic Table Mendeleev’s Dobereiner’s Triad Table (1869)...

Chapter 2 Week 3 Atoms and the Periodic Table Chapter Outline History of the Periodic Table The Modern Periodic Table Periodic Trends  History of Periodic Table Mendeleev’s Dobereiner’s Triad Table (1869) Modern Periodic (1817) Table (1829) Newlands’ Law of Henry Moseley Octaves(1866) (1864)  History of Periodic Table Dobereiner’s Triads (1817) John Dobereiner grouped elements which exhibit very similar characteristics in threes or triads. The atomic weight of the second element was found to be the average of the first and third elements. Johann Wolfgang Dobereiner  History of Periodic Table Newlands’ Law of Octaves (1866) When elements are arranged in order of increasing atomic masses, the properties of the 8th element are a repetition of properties of the 1st element John Newlands  History of Periodic Table Mendeleev’s Table (1869). Dmitri Mendeleev, a Russian chemist, discovered that the atomic weights of the elements were related to the periodic variation in their properties. Dmitri Mendeleev  History of Periodic Table Henry Moseley (1894) suggested that it was the charge of the nucleus and not the atomic weight that accounted for the periodic trends in the properties of the elements. The modern periodic law is stated as ‘properties of elements are a function of their atomic number.’ Henry Mosley The Modern Periodic Table M O Nh Ts c g  The Modern Periodic Table  Metals Are solids at room temperature (except for Hg, which is liquid), shiny, conduct electricity, and are ductile and malleable. Form alloys (solutions of one metal dissolved in another); brass, for example, is an alloy of copper and zinc. In chemical reactions, they tend to give up electrons.  Nonmetals Except for hydrogen (H), they lie on the right side of the Periodic Table. Do not conduct electricity. In chemical reactions, they tend to accept electrons. The Modern Periodic Table M O Nh Ts c g  Periodic Trends Periodic Table was constructed based on trends (periodicity) in chemical properties. Chemists realized that the periodicity of chemical properties could be understood in terms of periodicity in electron configuration. The Periodic Table worked because elements in the same column (group) have the same configuration in their outer shells.  Periodic Trends: Atomic Radius The size (radius) of an atom is determined by the distance from the nucleus to the outermost occupied electron shell. In general, atomic size increases with increasing number of electron shell down a group in the periodic table.  Periodic Trends: Electron Affinity Electron affinity is the amount of energy released or exerted when an atom gains an electron. It is the ability of an atom to gain additional electrons which depends on the attraction between the electron and the nucleus of an atom.  Periodic Trends: Ionization Energy Ionization Energy of an atom is the energy needed to separate an electron or electrons from a gaseous ground state atom. The farther the distance of an electron from the nucleus, the more easily it can be removed.  Periodic Trends: Electronegativity Electronegativity describes the ability of an atom to attract electrons to itself. It is related to ionization energy and electron affinity since these quantities reflect the ability of an atom to form cations and anions.