Chemistry Open-book Paper - Periodic table and Atomic structure

Gallium was discovered in 1875 by a French scientist Paul Boisandram. Gallium is an unusual element since it is in a borderline situation where by it can act as a metal or non-metal depending on the situation.

There are two sides of the controversy on Gallium; these are both physical and chemical. The first is the pH of the oxides of Gallium; metallic elements should make base oxides whilst non-metallic oxides are acidic. Gallium dissolves in both acid and alkalis, which is unusual but it follows the example of aluminium which is above in the same group.

Ionic oxides are base and covalent oxides are acid and neutral.

For instance, 2Na+O2- (s) + H2O (l) --> 2Na+ (aq) + 2OH- (aq)

2Ga (s) + 2OH- (aq) + 6H2O (l) --> 2[Ga(OH4)]- (aq) + 3H2 (g)

Both show ionic oxides are base

SO3(s) + 2H2O (l) --> H3O+ (aq) + HSO4- (aq)

2Ga (s) + 6H+ --> 2Ga3+ (aq) + 3H2 (g)

Both show covalent oxides are acidic

This shows that Gallium acts as both metal and non-metal

An atomic spectrometer is where atoms can get excited by absorbing energy from heat, electrical discharge or radiation. This atomic excitement causes the electrons to gain energy and go up energy levels. Once it begins to lose energy and return to ground state, the electrons return to their initial levels giving off energy in the form of radiation. A spectrometer is used to give lines that are called monochromatic lines. This radiation is usually visible, infra-red or ultraviolet. The colour and wavelength is used to determine the element. This is Bohr's theory created by Danish scientist Niels Bohr. For instance with hydrogen the one electron can go up energy levels (shells) 1-3 therefore there would be three lines in the visible, and one ultra violet and 3 infra-red lines in the spectrum.

This spectrum was produced by exciting a glass tube of hydrogen gas with about 5000 volts from a transformer

This UNILAC accelerator was created by a team called GSI. The linear accelerator fires a beam of heavy ion bombarding a stable element to attempt to fuse them together and create a new element, this requires sufficient violence to overcome the natural repulse of the nuclei. The element Ds 110 was created by directing a high-energy beam of nickel-62 atoms generated from the GSI heavy-ion accelerator, known as UNILAC, at lead-208 targets on the circumference of a wheel rotating at 1,125 rpm.

These studies using both the UNILAC accelerator and atomic spectroscopy have increased our knowledge about the periodic table by not only discovering many new elements, but also by understanding the elements already known. Until 1899 the smallest thing was the atom, since then we have been able to spit it and found electrons, protons and neutrons. For years scientists have concentrated simply on electrons and Neils Bohr in 1913 published an emission spectra that suggested that electrons had shells and sub-shells, and that they moved round the nucleus in orbits.

Recently research has been done on the nucleus, shell and sub shells have been established. These allow scientists to reliably predict the stability of elements. These shells have the same principle as the electron shells, this means when the outer shell is full the element is stable. The number of proton required to fill the shell is called "Magic number". There are different shells for protons and for neutrons. The UNILAC accelerator relies on the fact that the nucleus of one element can join with an ion to create a new element.

For the UNILAC accelerator the atomic structure allowed the scientists to know that a considerable force is required to overcome the electron cloud and repulsive forces of the nucleus.

Atomic Spectroscopy relied on the rules of electron configuration, and the knowledge of energy levels. Without the understanding of energy levels we would not be able to interpret the colours and lines that are given in the spectrometer.

In the late 1700's only 30 elements had been identified, like gold and copper. In the early 1800's scientists started using new laboratory techniques to find new elements. Within 100 years the known elements were doubled.

Until recently scientists have been working mainly on finding the electron configuration, ions and reactivity. As shown earlier this electron study has evolved to spectroscopy and various other things. Yet lately more attention has been paid into the nucleus of the atom, and they have discovered shells and sub shells that can determine the stability of an element.

In the last decade scientists are no longer searching for existing elements, but manufacturing them. Unfortunately they are at such a level that the elements that they are making only last fractions of a second. Many scientists find this pointless since there can't be any real application of these elements. Although in theory, element 114 if made at the right isotope may last for years, since its neutron and proton both fill their outer shell ('double magic') and therefore it's very stable, has not been found at such a stable state yet.

The problem is that when discovering new elements the next one is 3 to 4 times more difficult. These days scientists have found particles that are even smaller than electrons. They think that all sub-atomic particles are themselves made up of yet smaller particles called Quarks.

References:

Gallium: A landmark in the history of chemistry

The New Alchemists

Chemical Ideas - Heinemann

Chemistry in Context - Graham Hill & John Holman

A-Level Chemistry - E.N.Ramsden

Mechanics and Radioactivity - Mark Ellse & Chris Honeywill

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www.webelements.com