Moseley is another chemist who has aided in the development of the periodic table. He realized that the atomic numbers were not just a convenient numbering scheme for the elements, but had a real physical meaning - ultimately realized as being the number of protons (and electrons) in a (neutral) element.
English chemist John Newlands, having arranged the known elements in order of increasing atomic weights, noted that after interval of eight elements similar physical and/or chemical properties reappeared. Newlands was the first to formulate the concept of periodicity in the properties of the chemical elements. He called this the Law of Octaves; Elements exhibit similar behavior to the eighth element following it in the table.
Mendeleev stated that the elements vary periodically according to their atomic masses. He separated his elements and left spaces on his table in order for the periodicity to continue. He then predicted that elements would be discovered to fill these "gaps" in the table. Mendeleev even accurately stated the properties of the elements: Scandium gallium, and germanium. By 1886 all the elements he predicted had been isolated.
The biggest difference between Mendeleev’s and earlier attempts to classify the elements was that Mendeleev's Table allowed for and was capable of adjusting to future discoveries
Gallium was discovered by Boisbaudran after studying its properties he found that they coincided with those that Mendeleev had predicted a few years earlier for eka-aluminum, the then undiscovered element lying between aluminium and indium in his periodic table.
2) Describe and explain why the properties of gallium are considered to be unusual, identifying the properties that suggest gallium is a metal and those that suggest it is a non-metal.
Gallium melts near room temperature and has one of the largest liquid ranges of a metal. (So it has found use in high temperature thermometers). This is because gallium has a high boiling point and a low melting point, and also has a low vapour pressure even at high temperatures.
Gallium is denser as a liquid than as a solid. This is probably because the solid gallium has a more open structure than the liquid.
Properties that Suggest Gallium is a Non-Metal
The low melting point of gallium is a property that suggests it is a non-metal. The fact that it is denser as a solid than a liquid (like water) does so also.
Properties that Suggest Gallium is a Metal
Gallium also has many physical and chemical properties of a metal. It is shiny and conducts heat and electricity very well. Gallium easily forms alloys with most metals and has been used to create low melting alloys.
3) Describe how atomic spectroscopy and the UNILAC accelerator have been used to increase our knowledge about chemical elements in the Periodic Table. Explain how each technique works and show how both techniques rely on the understanding of the structure of the atoms.
UNILAC Accelerator
The UNILAC accelerator is used to fire ions at a rotating disk of a target metal. Ions are injected into the injectors (1) and then pass into the high-charge injector before being fired into the next structure at about 5% of the speed of light. By the time it has reached the end of UNILAC, the ion beam has reached 16% of the speed of light. Part of the beam is then diverted to the adjoining experiment hall for experiments, while the remainder is transferred to the heavy ion synchrotron SIS for further acceleration. There, the ions reach up to 90% of the speed of light. Such high speed produces enough force for the ions to overcome the repulsion of the nuclei and fuse together, forming a new element.
Atomic Spectroscopy
4) Discuss how the work of Chemists has changed over the last two hundred years from discovering the elements to synthesising elements
The time when elements were first being discovered, it was important for the chemists at the time to discover all the elements. When most of the elements had been discovered people like Mendeleev, De Boisbaudran Newlands and others started to classify and categorize the discovered elements based on their behavior.
After Mendeleev’s ‘gaps’ had been filled in, chemists discovered the noble gasses.
Once all the 92 naturally occurring elements had been found, scientists decided to synthesise new ‘artificial’ elements. Scientists now can turn an element into another, which is a lot more precious, whereas the medieval chemists only dreamt of turning base metals into gold. However, as these elements are unstable with a half-life so short that any atoms of the of the elements may have been may have been present when the earth formed, but have long since decayed away. Hence are only known to us as the products of UNILAC accelerator (see point 3).
