Periodic Table Research Task

Topics: Chemical element, Periodic table, Chemistry Pages: 8 (2751 words) Published: March 25, 2013
Periodic Table Research Task By Kevin Shaji
Part A. You are to research the task below and submit as a written piece of work i) John Dalton proposed his atomic theory in 1808. Outline his theory. (4 marks) ii) Explain which part of Dalton’s atomic theory was later found to be incorrect. (3 marks) iii) Dalton developed a way to measure the relative atomic mass of the different elements. Using examples research and describe the meaning of the term ‘relative atomic mass’. (3 marks)

i) 1) Elements are made up of tiny particles called atoms. 2) Atoms cannot be destroyed or created but can be rearranged during chemical changes. 3) Atoms of a particular element are identical in mass, size, shape and other properties. 4) Atoms of different elements are different in their mass, size, shape and other properties. 5) Atoms cannot be divided into smaller particles.

6) Atoms of different elements combine in small whole-number ratios to form compounds.

ii) 1) One part of Dalton’s atomic theory that was later discovered to be incorrect was the part where atoms could not be divided into smaller pieces. New research has proved that atoms can be sub-divided into sub-atomic particles like protons, neutrons and electrons. 2) Due to the discovery of isotopes it has been discovered that atoms of the same element are not exactly identical. They have different masses due to the number of neutrons. 3) Also it has been discovered that different elements have the same mass. These elements are called isobars. 4) It has been recently discovered that atoms can actually be destroyed by fission processes in atomic reactors or by atomic bombs. 5) Another defect in Dalton’s atomic theory is that not all compounds have small whole-number ratios. They can actually have large whole-number ratios as well.

iii) The relative atomic mass is defined as: “the average mass of the isotopes in a naturally occurring sample of the element, taking into account the proportion of each isotope present.” The symbol for relative atomic mass is Ar. For example naturally occurring chlorine has two isotopes Cl-35 and Cl-37. Cl-35 has a relative abundance (which is the percentage of that isotope on Earth in relation to the total abundance of the atom on Earth) of 75% while Cl-37 has a relative abundance of 25%. To calculate the Ar you must put the above into a formula.

Ar= (75/100×35) + (25/100×37) =35.5

Another example of calculating relative atomic mass is:

For an element E with the naturally occurring isotopes aE, bE, cE, and with the respective abundances of A%, B%, C% etc, the relative atomic mass (Ar) = (A/100 x a) + (B/100 x b) + (C/100 x c)

Part B
Leucippus was an early pre-Socratic ancient Greek philosopher who lived sometime during the 5th century BCE. Not much of Leucippus early life is known due to the fact that not many of his dates were recorded. What we do know is that he was an Ionian Greek that studied at an Ionian school of naturalistic philosophy. At around 440 BCE Leucippus founded a school at Abdera, which his famous pupil Democritus attended. Around this time he proposed the theory of atomism. According to this atomism, the universe is composed of two elements: the atoms and the void in which they exist and move. This theory was later explained in much greater detail by his pupil Democritus. Leucippus contributed indirectly towards the development of the periodic table since he proposed the first idea of atoms. Thanks to his ideas the foundation for the periodic table was possible. Without his ideas the way we view the world may be completely different. Democritus

Democritus was an influential pre-Socratic ancient Greek philosopher who lived from circa 460 BCE to circa 370 BCE. He inherited his father’s vast fortunes and used it to travel the world and visit many countries on his quest of knowledge. During these trips he met many scholars who taught many lessons. When he finally came back...
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