Standard level
Atomic radius is dependent on the type of matter under consideration. It could be the atomic (van der Waals) radius, the metallic radius or the covalent radius. In this experiment the students will investigate the metallic radius.
Background
Metals are made up of many atoms joined together by delocalised electrons. The metal atoms could indeed be considered ions surrounded by delocalised electrons - it's arguable. What is true is that the metal atoms/ions are pulled tightly together and adopt the most efficent packing system, known as close-packing, in which each atom is surrounded by 12 nearest neighbours.
However, the atoms do not occupy all of the space. There are small holes which account for 26% of the available volume.
Hence, if we know the measured volume and mass of a sample of metal, the mass will provide us with the number of particles (moles), and the volume of 1 particle can then be calculated.
Assuming the atoms to be spherical, allows us to determine the atomic radius using the formula:
Volume of a sphere = 4/3πr3
Chemicals
- Metal cube samples, all 2cm x 2cm x 2cm
- Aluminium
- Copper
- Iron
- Zinc
Apparatus
- Electronic balance
- Weigh a metal cube.
- Divide the mass, in grams, by the relative mass of the metal.
- Calculate the volume of the cube in m3.
- Calculate the actual volume occupied by the atoms.
- Calculate the volume of 1 atom.
- Determine the atomic (metallic) radius.