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The Periodic Table Elements are arranged in a way that shows a repeating, or periodic, pattern. Dmitri Mendeleev created the first periodic table of the elements in 1869. He ordered the ~70 known elements by their atomic masses and their chemical properties. He found that some elements could not be put into groups with similar properties and at the same time stay in order. Mullis 1 Modern Periodic Table Later, Henry Moseley carried on the work. Moseley put the elements in order of increasing atomic NUMBER. He found that the position of the element corresponded to its properties. The modern periodic table shows the position of the element is related to : Atomic number AND Arrangement of electrons in its energy levels Mullis 2 Atomic Sizes using Periodic Table As we move down a group, atoms become larger. Larger n = more shells = larger radius As we move across a period, atoms become smaller. More protons = more effective nuclear charge, Zeff More positive charge increases the attraction of nucleus to the electrons in the outermost shell, so the electrons are pulled in more “tightly,” resulting in smaller radius Mullis 3 Ionization energy Ionization energy of an ion or atom is the minimum energy required to remove an electron from the ground state of the isolated gaseous atom or ion. The first ionization energy, I1 is the energy required to remove one electron from an atom. Na(g) Na+(g) + e Larger ionization energy, harder to remove electron. 4 Fig. 8.11 5 Periodic Trends in Ionization Energy Highest = Fluorine Ionization energy decreases down a group. Easier to remove electrons that are farther from the nucleus. Ionization energy increases across a period. Zeff increases, so it’s harder to remove an electron. 6 Electron Affinity Electron affinity is the energy change when a gaseous atom gains an electron to form a gaseous ion. Gain Electron affinity: Cl(g) + e- Cl-(g) Lose Ionization energy: Cl(g) Cl+(g) + e- 7 Electronegativity Electronegativity is the ability of an atom in a compound to ATTRACT an electron. F has the highest electronegativity. (She is “SO ATTRACTIVE!”) 8 Metals Metallic character increases down a group and from left to right across a period. Metal properties: Lustrous (shiny) Malleable (can be shaped) Ductile (can be pulled into wire) Conduct electricity Metal oxides form basic ionic solids: Metal oxide + water metal hydroxide Metal oxides react with acids to form salt and water 9 General Trend Summary Fr Atomic Radius, Metallic Character F Electronegativity, Ionization Energy, Electron Affinity Atomic Radius, Metallic Character Electronegativity, Ionization Energy, Electron Affinity 10 Mullis 11 Ionization energy Ionization energy of an ion or atom is the minimum energy required to remove an electron from the ground state of the isolated gaseous atom or ion. The first ionization energy, I1 is the energy required to remove one electron from an atom. Na(g) Na+(g) + e The 2nd ionization energy, I2, is the energy required to remove an electron from an ion. Na+(g) Na2+(g) + e Larger ionization energy, harder to remove electron. Mullis 12 Periodic Trends in Ionization Energy Highest = Fluorine Ionization energy decreases down a group. Easier to remove electrons that are farther from the nucleus. Ionization energy increases across a period. Zeff increases, so it’s harder to remove an electron. Exceptions: Removing the 1st and 4th p electrons Mullis 13 Electron Affinity Electron affinity is the energy change when a gaseous atom gains an electron to form a gaseous ion. Electron affinity: Cl(g) + e- Cl-(g) Gain Ionization energy: Cl(g) Cl+(g) + eLose Mullis 14 Electronegativity Electronegativity is the ability of an atom in a compound to ATTRACT electrons. Fluorine has the highest electronegativity. Fluorine is “SO ATTRACTIVE!” (bats eyelashes) Mullis 15 Metals Metallic character increases down a group and from left to right across a period. Metals are found to the left of the zig-zag line on the periodic table. Metal properties: Lustrous (shiny) Malleable (can be shaped) Ductile (can be pulled into wire) Conduct electricity Metals form cations (positive ions) This means they lose 1-4 electrons Therefore, they are usually found in IONIC compounds Mullis 16 Nonmetals Lower melting points than metals Diatomic molecules are nonmetals. The seven (7) diatomic molecules are: Br2 I2 N2 Cl2 H2 O2 F2 Two or more nonmetals form molecular compounds with COVALENT bonds. Mullis 17 Trends See your book for full explanation. Closer to F = more ELECTRONEGATIVITY ELECTRON AFFINITY IONIZATION ENERGY Closer to Cs = more METALLIC CHARACTER ATOMIC RADIUS REACTIVITY Mullis 18