Lab 4
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 Forceps or tongs Water 10 ml graduated cylinder
Safety Gloves Safety goggles/glasses
Background Dmitri Mendeleev arranged the Periodic Table in groups and in order of increasing atomic mass.
Background Henry Moseley rearranged the Periodic Table in order of increasing atomic number (Z).
Background Atomic number (Z) Number of electrons and protons Ex: Cr 24 Atomic mass (M) Z + number of neutrons Ex: M Cr = 52 amu
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) = amu. 1 amu = 1.66 x kg. (Show calculation)
Background (Periodic table) Property of an element depends on the location (family = vertical column; period = horizontal row).
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
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
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