Six years later in 1869 professor Dimitri Mendeleev came up with a periodic table that ours is based on today. A whole new group was added as the noble gasses were found; all the gaps have been filled. Elements are arranged in order of increasing atomic number, rather than relative atomic mass. He amended some relative atomic masses and he also left gaps for undiscovered elements. For the gaps in his table, he predicted the properties of these undiscovered elements. He predicted the properties of an element he called eka-aluminium. He was proved right in 1875, the element was called gallium; its properties are in excellent agreement with Mendeleev’s predictions.
Gallium is unusual because it has such a low melting point (29.78ºC). In hot countries it becomes a liquid metal like mercury. It is also unusual because of its high boiling point (2403ºC). It has the widest liquid range of any element. It shares the same property as water for being denser as a liquid than as a solid at its freezing point. Hence it will solidify from the top down. However it closely resembles a similar metal in its appearance (aluminium). Like aluminium, it dissolves in both acids and alkalis. Evolving hydrogen. Only a few metals behave in this way. These metals all have amphoteric hydroxides.
The UNILAC accelerator involves firing a beam of relatively heavy ions from an accelerator towards a target of a heavy, stable element such as lead. If this is done with sufficient violence, the ions overcome the natural repulsion of the nuclei and fuse together, creating a new element. In 1981 the GSI team scored its first success by firing a beam of chromium ions at a rotating target of bismuth metal. The problem is that the elements have very short half-lives, so they soon change into other elements. The accelerator has made more elements that fit into the periodic table. An understanding of the structure of atoms is needed to understand how it would be possible to fuse together 2 nuclei.
Atomic spectroscopy, a source of white light is shone through a sample burning in a flame, the light then travels through a slit and then into a prism where an image of black lines on a bright coloured background. It shows the composition of the sample. Atomic spectroscopy is widely used to find the composition of a sample of steel or to estimate the sodium content of blood. The composition of stars can be determined from vast distances away by using this technique. An understanding of the structure of atoms is needed to understand how atoms absorb energy and how they emit it, and what you can tell from the emitted energy.
The role of chemists has dramatically changed over the past 200 years. Medieval chemists (alchemists) goal was to turn base metals into gold. As the years went by their role changed, in the 1700’s they were now looking to discover and find new elements. Today they are creating the elements them self (synthesising new elements). Once the scientist had stopped discovering elements, they went about making their own this has only been possible due to our technology. The UNILAC accelerator has only just been invented in the past 20 years and so when it was invented it still took some years to synthesize the new elements and even then they don’t last long because they have very short half lives. The advance of chemistry has mainly been down to the advances in technology. You could say that with out the advances in technology most of the discoveries man has made would not exist. In the future we are probably likely to find more elements and have a better understanding of the elements themselves.
Bibliography
http://www.periodictable.com/pages/AAE_History.html
Salters advanced chemistry, chemical storylines, Heinemann
Salters advanced chemistry, chemical ideas, Heinemann