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By finnjess Jun 05, 2013 1723 Words
Science Assignment| March 22
Jessica Finney| Ms Croaker – Sc743A |

Science Part A Assignment

Choose one scientist involved in formulating the modern periodic table and describe why their work made a significant contribution to the development of the periodic table. Dmitri Mendeleev’s contribution to the modern day periodic table is widely renowned in the history of chemical science. Mendeleev was the creator of the periodic table; arranging 63 known elements in order of their atomic mass. His discovery made a significant impact in the development of the periodic table as it set the foundation for further progress to occur in the future. Dmitri Mendeleev anticipated the existence of new elements to be discovered, therefore leaving gaps in the ascending order of elements. Mendeleev was the notable discoverer of isotopes and rare gasses. In summary, science is a blend of logic and imagination and Mendeleev demonstrated these attributes through developing the periodic table (Western Oregon University, 2012). Dmitri Mendeleev’s creation of the periodic table was considered one of the greatest triumphs in chemistry history as it allowed for further exploration to begin.

Why do you think the development of the periodic table required input from a range of different people? As many are aware, the development of the periodic table required numerous scientists such as John Newlands and Julius Lothar Mieyer. If not for these men, Mendeleev’s table would not be as accurate as it is today. As time progressed, technology advanced scientists’ discovered noble gasses and determined each elements atomic number. Many scientists played a vital role in developing our modern day periodic table as each person had a different knowledge and understanding of chemistry. To conclude, the periodic table was never one man’s discovery, but the result of numerous scientists’ explorations and experimentations. Each played a vital part in challenging/confirming the theories of their predecessors, recognising different patterns and properties between different elements.

How did improvements in technology influence the development of the periodic table? With the improvement in technology from the 1800’s through to present day the development of the periodic table has undergone significant changes. Since the development of the table by Dmitri Mendeleev in 1869, scientists have utilised new technologies to produce a more accurate representation of the chemical elements. Scientists such as William Ramsay, who discovered noble gasses, drastically changed the periodic table adding a whole new group. In 1913, Henry Mosely significantly affected the periodic table with his discovery of nuclear charge. Ultimately, the most technological change is attributed to Glen Seaborg in 1940. His work on the discovery of atomic number reconfigured the periodic table, awarding him the noble prize in chemistry in 1951.Without technological advancements such as nuclear reactors, telescope and the chemical bonds system (Alexander Crum Brow)).Seaborg possibly would not have been able to discover what he did. In summary, the advancement in technology has importantly altered Mendeleev’s original periodic table and will most likely continue with new synthetic elements being added.

Briefly describe information we now have about atoms that was not available to earlier scientists who were identifying patterns and trends within early versions of the periodic table. What trends could they see, compared to what we now know? In the 20th Century, scientists have a greater understanding of atoms and the patterns they follow compared to those who invented the early versions of the periodic table. It was noted in the early 1800’s, that matter consisted of lumpy particles called atoms. Towards the end of the century, J.J Thompson discovered electrons and their negative charge. He hypothesised that atoms would therefore contain positive charged particles. In 1869, scientists began to recognised patterns in properties originating from a number of known elements, eventually developing the classification methods. During the early versions of the periodic table, it was determined by Henry Mosely to arrange elements in order of their atomic number. This pattern followed the periodic table concept more accurately than the arrangement of atomic weight. Another notable trend originated from glen Seaborg in the 1940’s. Seaborg artificially produced new heavy mass elements such as neptunium and plutonium. Thus creating a new block in the table called ‘antinides’. To conclude our knowledge of atoms, their structure and patterns they form in the periodic table originating from the 18th century has developed. Essay Part

This essay will provide a clear insight into the element of chlorine. It will include detail on the history of chlorine, its’ structure, position on the periodic table and the ions formed. The element of Chlorine was discovered quite early compared to many other elements. Carl Wilhelm Scheele first produced the element in 1774 in Sweden. Scheele came across this element after combining the mineral pyrolusite and hydrochloric acid together. He discovered that this new gas reacted with metals, dissolved slightly in water and bleached flowers and leaves. At first, Scheele believed that the gas produced was oxygen, however Sir Humphry Davy proved in 1810 that this gas was new. Sir Davy then went on to name the new substance Chlorine after the Greek word (Chloros) meaning greenish yellow. Chlorine’s element structure is similar to other elements that are situated in the halogens group on the periodic table. This element comprises an atomic number of 17 and weight of 35.5. Chlorine is known to be an extremely reactive gas therefore providing reasons as to why it directly combines with the majority of other elements except for the noble gasses. This element is arranged into three shells. The first two shells are filled with electrons. Meanwhile the third contains only seven electrons. Chlorine is a naturally occurring element, arising in the Earth’s crust and seawater. It’s abundance in the Earth is about 100-300 parts per million (Chemistry Explained, 2013). This element is considerably well known to be a dense gas, containing a density rating of 3.21g per litre. Chlorine is quite a strong oxidizing agent. In other words, it is notorious for taking on electrons from other substances. Nevertheless, the element chlorine’s specific element structure dictates as to why it is positioned within the halogens group. Chlorine has been specifically positioned within the periodic table situated in group 17 because it belongs to the halogens family. It is known to be the second lightest element in the halogens group. Chlorine is situated in this group because it contains similar chemical properties to other halogen family members. Some chemical and physical properties of these elements are; that are very reactive, they contain seven valence electrons, they are poor conductors and they are brittle when solid. Chlorine has a melting point of -100.98°Cand a boiling point of -34.6°C. Chlorine is heavier than air and proved very effective as a chemical weapon in the trenches and fox holes dug in World War One. Chlorine has been specifically positioned towards the top end of the halogens as it holds a notably low atomic number compared to other elements that are also a part of the same group. In summary, Mendeleev and Seaborg essentially position chlorine within the halogens group due to its similar characteristics. The elements included in the halogens group are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Fluorine and chlorine, both have seven valence electrons in their outer shell. That seven-electron trait applies to all of the halogens. They are all just one electron shy of having full shells. The halogens have the trait of combining with many different elements. They are very reactive. You will often find them bonding with metals and elements from Group One of the periodic table. Fluorine is the most reactive of the halogens and reactivity decreases as you move down the column. Therefore, Chlorine is the second most reactive. As the atomic number increases, the atoms get bigger. Their chemical properties change just a small amount when compared to the element right above them on the table.

Chlorine forms a negative ion by reason of a greater amount of electrons than protons. This atom has 17 protons and electrons. Due to the last unfilled electron shell, this element transforms into a negative ion. In simpler terms, a negative ion contains one more electron than proton. In scientific language, a negative ion is otherwise known as an anion. Chlorine is converted into an ion once gaining an extra electron from a different element. This process is essential for creating an ionic bond. Chlorine’s ion is known to be extremely soluble in water, thus giving reasons as to why it bonds with sodium, forming sodium chloride. The ionic bond that forms is measured in terms of valence, meaning how much an element wants to bond with another element. To summarise, chlorine and sodium are a direct example of an ionic bond that forms when two ions chemically attach together. The uses of chlorine in everyday life are vast and continue to be used world-wide specifically for maintaining a clean swimming pool environment and many uses as a cleaning agent.

* Alchin, L.K 2012,’ Periodic Table Video’, The Periodic Table, viewed 17th February, * Campbell, 2011,‘Dmitri Mendeleev’, Kiwi Web Chemistry & New Zealand, 5th February 2013, *

* ‘Chlorine atom, Sodium atom’, Ions, viewed 18th February 2013, * Chemistry Explained, ND,’ Chlorine’, viewed 5th February 2013, * Gagnon, S ND,’ The Element of Chlorine’, Jefferson Lab, viewed 8th February 2013, * ‘Dmitri Mendeleev’ viewed 10th February 2013, * Helmenstine, A.M 2013, ‘Chlorine Facts’, Chemistry, viewed 7th February 2013, * * ‘History of the Periodic Table’, Aus-e-tute, viewed 11th February 2013, * Lenntech, B.V 2012,’ Chlorine – Cl’, Water Treatment Solution Lenntech, viewed 6th February 2013,

* Rader, A 2012,’ Looking at ions’,, viewed 18th February 2012, * Solar Power Facts 2012,’ The Element chlorine: Structure and Properties’, viewed 9th February 2013,

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