1. Lab 4

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) Z Cr = 24  Mo (35 to 40 g)Z Mo = 42  W (55 to 60 g)Z W = 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: M Cr = 52 amu

8. Background  Atomic Mass (M)  Some of the mass of an element is converted into energy (nuclear binding ), E = mc 2.  Ex: Tungsten (Z = 74; M W = 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) – E min 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