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Chemistry presentation

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candy loyola

on 4 April 2011

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Transcript of Chemistry presentation

Chemistry Presentation -
Periodic varitation of properties. Hannah and Candy 2a) Which properties of the elements display periodic variation? Periodic Variation is seen in the atomic radius and firstionisation energy of the first 36 elements. The pattern of the atomic radius decreases steadily from left to right across the periods and increases down the groups. The decrease across a period is due to the increasing positive charge of the nucleus, attracting the outer shell electrons closer. The increasing electron configuration down a group is cause for the increase in atomic radius. b) Which properties do not display periodic variation? Periodic Variation is not seen in the melting temperatures and the density of elements. c) Give reason why not all properties display periodic variation. The figures of these properties are not in constant/regular increase or decrease but instead fluctuate in such a way that no pattern can be seen. For the melting points of the elements this is due to whether or not an element is metallic or non metallic. Whether an element is a gas, liquid or solid at 298 K ( g mL -1) detemines the elements density. It is these inconstant properties that make them not dislay periodic variation. 1) Use a spreadsheet program to plat graphs to show how the following characteristics of the elements vary with atomic number.

a) number of electrons in the outter most shell.
b) density.
c) melting temperature.
d) atomic radius.
e) first ionisation energy 3) Explain the trend observed for atomic radius and first ionisation energy:
a) From left to right across a period.
b) down a group. In first ionisation energy, a decrease is seen down a group as the atoms increase in the number of shells they posses and a increase is shown across the periods from the energy required to move the outtermost electrons from an atom with an increase in strength of atraction between the outtermost electrons and the nucleus. 4a) Use the graphs from Question 1 ro predict the properties of the element 37. We would know that it is not a gas and that the melting temperature would be under 500. The atomic radius would be fairly large as it has more shells and that the ionisations energy would be under 0.5. b) Use a book of chemical data to find the actual values for the properties of element 37 and compare the actual values with your predicrions. We found that Rubidium may be a liquid at room temperature and that it is a metallic element of the alkali group. Atomic radius is 248 and the ionisation energy is 402.8 5) Which of the data in the table were available to Mendeleev when he was developing his Periodic Table? Mendeleev only knew the similar chemical properties and the increasing atomic weight. 6) Explain how Medeleev usde the data available to him to create his Periodic Table In 1869, Dmitri Mendeleev constructed a periodic table by arranging the elements in order of increasing relative atomic mass into horizontal periods and arraging those with similar chemical properties into verticle groups. 7) Why were there gaps in Mendeleev's table? He left gaps in his periodic table for elements yet to be discoverd as there were only 63 elements known at that time. He also was able to predict the properties of undiscoverd elements on the basis of his table and the gaps he had left. Sorry if we bored you :D
thanks for watching (:
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