lab 4. goals of the experiment measure bulk densities & calculate atomic densities of some...
TRANSCRIPT
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) ZCr = 24
Mo (35 to 40 g) ZMo = 42
W (55 to 60 g) ZW = 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: MCr = 52 amu
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)
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) – 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
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