Atomic Size

Introduction

The goals of this lab are to measure atomic and molecular size in solid/liquid/gas; to estimate the "packing coefficient" for atoms in solids; and to prepare a monolayer film of oleic acid and use its experimental measurements to estimate the value of Avogadro's number. To measure atomic size in solids, cubical and spherical atomic models would be used; to examine the packing coefficient in solids, the empty space between atoms of the cubical model would be calculated; to measure Avogadro's number, a monolayer film of oleic acid would be measured in size then calculated in thickness and volume to derive statistical numbers.

Experimental Procedure

For the measurement of atomic size in solids, two cylindrical samples of aluminium and copper were obtained, weighed, and measured in volume through water displacement. Then density was calculated and estimated in its atomic size with the cubical atomic model. A small bottle of lead shot was also used to experimentally estimate the value of the packing coefficient. A 10 mL graduated cylinder was taken, filled with lead shot to about 10.0 mL and the total empty space volume between the lead balls was found.

For the measurement of molecular size in liquids and solids, a clean 50 mL graduated cylinder was weighed and had 20 mL of distilled water added to it. The mass difference between the exact volume of water and the exact mass of the graduated cylinder was used to calculate the water density and the molecular size of the water molecules.

For the measurement of molecular size in solids and gases, a measured solid dry ice sample was placed in a 125 mL glass flask, and a rubber balloon was placed over the neck of the flask. Once the whole dry ice pellet in the flask sublimates into carbon dioxide, the final gas volume in the balloon would be recorded then calculated in molecular size.

For the measurement of Avogadro's number, oleic acid molecular length was measured with the monolayer technique. Calibration of the pipet was an important process in this experiment, as an accurate average volume of a drop of oleic acid would have influenced experimental data. A petri dish was filled with distilled water to ¾ full and settled to rest for 1 minute on a level surface. Then the water surface was dusted with lycopodium powder. A drop of oleic acid was added to the petri dish and the spreading film pushed the powder away. After 10-15 seconds have elapsed, the ethanol completely evaporated from the acid film. Once the monolayer film stabilised, five measurements of the diameter were taken, the average value of the oleic acid molecule's length and its standard deviation were then calculated.

Discussion

For the measurement of atomic size in solids, slight experimental errors were encountered-ranging from 3.57% to 7.69%, the spherical