Nuts and Bolts Periodicity
Small, medium, and large nuts, bolts, and washers can be arranged in a matrix on an overhead projector in a 3X3 matrix so that similar hardware are in the same column. An analogy is drawn to the arrangement of elements in the periodic table.
This demo is usually used when the periodic table is first introduced. Allow about 10 minutes for this demo
Throughout the nineteenth century chemists struggled to find some kind of pattern within the known elements, some way of arranging them that would help to explain their similarities and differences:
- Johann Dobereiner, 1829 - Developed 'triads', groups of 3 elements with similar properties. Lithium, sodium & potassium formed a triad. Calcium, strontium & barium formed a triad.Chlorine, bromine & iodine formed a triad. This was a forerunner to the notion of groups.
- John Newlands, 1864 - The known elements (>60) were arranged in order of atomic weights and observed similarities between the first and ninth elements, the second and tenth elements etc. He proposed the 'Law of Octaves'. Newlands' Law of Octaves identified many similarities amongst the elements, but also required similarities where none existed. He did not leave spaces for elements as yet undiscovered. This was a forerunner to the notion of periods.
- Lothar Meyer, 1869 - Compiled a Periodic Table of 56 elements based on the periodicity of properties such as molar volume when arranged in order of atomic weight. Meyer & Mendeleev produced their Periodic Tables simultaneously.
- Dmitri Mendeleev, 1869 - Produced a table based on atomic weights but arranged 'periodically' with elements with similar properties under each other. Gaps were left for elements that were unknown at that time and their properties predicted (the elements were gallium, scandium and germanium). The order of elements was re-arranged if their properties dictated it, eg, tellerium is heavier than iodine but comes before it in the Periodic Table. Mendeleev's Periodic Table was important because it enabled the properties of elements to be predicted by means of the 'periodic law': properties of the elements vary periodically with their atomic weights.1
1AUS-e-TUTE, "History of the Periodic Table of the Elements." AUS-e-TUTE for Astute Students, 2 Aug. 2005, <http://www.ausetute.com.au/pthistor.html>
- small washer
- small nut
- small bolt
- medium washer
- medium nut
- medium bolt
- large washer
- large nut
- large bolt
Have a volunteer from the class arrange the objects in a single line on the overhead in order of increasing size. Ask the class if there is a pattern.
This demo is not particularly hazardous.