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Discovery of atomic structure and periodicity Dr. Orla Ni Dhubhghaill

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Presentation on theme: "Discovery of atomic structure and periodicity Dr. Orla Ni Dhubhghaill"— Presentation transcript:

1 Discovery of atomic structure and periodicity Dr. Orla Ni Dhubhghaill o.nidhubhghaill@ucc.ie

2 Early days - Philosophy Democritus (460 – 371 B.C.) Matter made up of atoms and space Aristotle (384 – 322 B.C.) Matter is continuous “Nature abhors a vacuum” http://dbhs.wvusd.k12.ca.us/webdocs/AtomicStructure/ AtomicStructure.html

3 Early Days - Philosophy 1417 – rediscovery of De Rerum Natura by Lucretius 14 th /15 th century – “Division of natural things has a limit” Aristotle’s teachings thought to be correct Atomic Theory = Godlessness 1624 (Paris) – death penalty for those opposed to Aristotle’s teachings Solution – Pierre Gassendi (1592 – 1655) Atoms are the smallest indivisible part of matter Created by God

4 John Dalton (1766-1844) "Having been in my progress so often misled by taking for granted the results of others, I have determined to write as little as possible but what I can attest by my own experience” Belief in atoms based on experimental evidence

5 Dalton’s postulates All matter is made up of atoms Atoms of the same element are identical, in mass and chemical properties When a compound is decomposed, the recovered atoms are unchanged; they can re- combine to form the same or new compound. Atoms of different elements combine in simple whole number ratios to form compounds http://www.slcc.edu/schools/hum_sci/physics/whatis/bi ography/dalton.htmlhttp://www.slcc.edu/schools/hum_sci/physics/whatis/bi ography/dalton.html http://www.rsc.org/publishing/journals/DT/article.asp?d oi=b307622ahttp://www.rsc.org/publishing/journals/DT/article.asp?d oi=b307622a

6 ‘Laws’ governing reactions Law of conservation of mass – Lavoisier, 1789 Total mass of products of chemical reaction is the same as total mass of reactants. Law of constant composition – Proust, 1797 Reacting elements combine in a constant ratio in a given compound

7 Dalton’s Law of Multiple Proportions If two elements combine to form more than one compound, then the amounts of one element that combine with a fixed amount of the other will differ by factors that are the ratios of small whole numbers

8 Dalton’s chemical symbols Adapted from Dickerson, Gray, Haight, Chemical Principles, 3rd edition, 1979

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