02. Charting matter
ATL
Information literacy skills: Present information in a variety of formats and platforms.
Use a periodic table of the elements to produce a table in a spreadsheet program of the nucleon number, A, and the proton number, Z, for as many elements as you can - but at least a minimum of 20 elements selected from the smallest to the largest proton numbers.
Program the spreadsheet with a formula to calculate the number of neutrons, N, for each of the elements. Copy the formula into your data table so that it repeats the calculation for all elements.
Now produce a scatter graph on your spreadsheet showing points for each of the atoms (N, Z).
Label the axes on your scatter graph clearly.
Now copy the column for Z again. Use this column to add a new data series to the scatter graph that shows the line N = Z.
Video instructions can be found here:
Analysis
Outline what you notice about the line for the actual existing elements compared with the line N = Z.
Assessment opportunity
In this activity you have practiced skills that are assessed using Criterion C: Processing and evaluating.
The curve for actual elements does not follow the line N = Z, but deviates upward from it at higher proton numbers. We can understand this deviation if we take a moment to apply what we already know about electrical forces to our model of the nucleus. If the nucleus consists only of protons and neutrons, then the only electrical charge present is the positive charge of protons. While the size of the proton charge is relatively small, at around 10-19 coulombs, the size of a nucleus is around 10-15 meters, so the protons are very close together indeed. Electrostatics would predict that nuclei should, in fact, fly apart due to the electrostatic repulsion between protons - but clearly they do not!
This fact led to the hypothesis of another force acting within the nucleus over very short range. The force needs to be attractive, and it needs to 'stick' nucleons together. The strong nuclear force is thought to be a leftover remnant of the forces that hold tiny sub-nucleon particle called quarks together within individual protons and neutrons. It is a rather special kind of force - it decreases very rapidly with distance, and it only acts on certain types of particles called hadrons.Since the strong nuclear force acts only over very short distances, it cannot hold very large nuclei together well, and these nuclei, therefore, need a proportionally greater number of nucleons to provide enough force to 'glue' them together.
The Japanese physicist Hideki Yukawa (1907 - 1981) who first postulated the existence of sub nucleonic particles that provided strong nuclear force.
