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Periodic Trends

Lab 4. Periodic Trends. Goals of the Experiment. Measure bulk densities & calculate atomic densities of some transition metals Relate density to atomic size (a periodic trend). Materials. Cr (25 to 30 g) Z Cr = 24 Mo (35 to 40 g) Z Mo = 42 W (55 to 60 g) Z W = 74

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Periodic Trends

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  1. Lab 4 Periodic Trends

  2. Goals of the Experiment • Measure bulk densities & calculate atomic densities of some transition metals • Relate density to atomic size (a periodic trend)

  3. Materials • Cr (25 to 30 g) ZCr = 24 • Mo (35 to 40 g) ZMo = 42 • W (55 to 60 g) ZW = 74 • Forceps or tongs • Water • 10 ml graduated cylinder

  4. Safety • Gloves • Safety goggles/glasses

  5. Background • Dmitri Mendeleev arranged the Periodic Table in groups and in order of increasing atomic mass .

  6. Background • Henry Moseley rearranged the Periodic Table in order of increasing atomic number (Z).

  7. Background • Atomic number (Z) • Number of electrons and protons • Ex: Cr 24 • Atomic mass (M) • Z + number of neutrons • Ex: MCr = 52 amu

  8. Background • Atomic Mass (M) • Some of the mass of an element is converted into energy (nuclear binding ), E = mc2. • Ex: Tungsten (Z = 74; MW = 184 amu). Actual mass (isotope) = 183.95093129 amu. 1 amu = 1.66 x 10-27 kg. (Show calculation)

  9. Background (Periodic table) • Property of an element depends on the location (family = vertical column; period = horizontal row).

  10. Background (Periodic Trends) • Atomic Radius • Increases from R to L; Increases from Top to Bottom (Show schematic view) • Ionization Energy (IE) – Emin required to remove 1 e- from an atom/ion in its ground state and it correlates to reactivity of metals (exceptions). • Increases from L to R; Decreases as you go down a family • Smaller IE = more reactive the metal

  11. Background (Periodic Trends) • Electron affinity (EA) - ∆E associated with the addition of an electron to an atom/ion & it correlates to the reactivity of nonmetals (exceptions). • Increases from L to R; Decreases as you go down a family. • Larger EA = more reactive nonmetal

  12. Background (Periodic Trends) • Density also displays a periodic trend – atomic density increases from top to bottom but varies less significantly as one moves from left to right across a period. • Bulk density depends on 3 properties: • Mass of the atoms • Packing arrangement (crystal structure – body centered, face centered, or simple cubic). • Size of each atom

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