ELEMENTS AND ATOMS

ELEMENTS AND ATOMSEvolution of the Element TheoryMonistsFour Elements and AlchemyPhlogiston and the Study of AirsLavoisier and ChemistryDiscovery of ElementsElectrolysisSpectroscopyPeriodic LawsThe ElectronDiscovery of the NucleusModels of the AtomThe Presocratic MonistsAll material is made of one elementary substance:Thales of Miletus (624-546 BCE): all is waterAnaximander of Miletus (610-546 BCE): all is apeironAnaximenes of Miletus (585-528 BCE): all is airHeraclitus of Ephesus (535-475 BCE): all is fire (=change)Pythagoras of Samos and Croton (570-495 BCE): all is numberDemocritus of Abdera (460-370 BCE): all is atomFOUR ELEMENT THEORIESAttributed to Empedocles of Agrigentum (490-430 BCE) and formalized by Aristotle of Stagira (384-322 BCE). According to Aristotle in hisOn Generation and Corruption:Airis primarily wet and secondarily hot.Fireis primarily hot and secondarily dry.Earthis primarily dry and secondarily cold.Wateris primarily cold and secondarily wet.

FOUR HUMOR THEORYHumor (, chymos = sap or juice)Formalized by Hippocrates of Kos (460-370 BCE) who tied a mechanistic theory of disease to the 4 elements and the weather.

INFLUENCE OF ALCHEMYEgyptian material religion [Khemeia (), meaning black (for the hidden arts) or black earth (an ancient reference to Egypt)]. With arabic prefix al-, it becomes al-khemeia or alchemy.Purpose to improve materialUsed careful methods and precise measurementsIntroduced to Greek Natural PhilosophyContinued and augmented by alchemists in the Islamic Empire

Paracelsus and IatrochemistryTook name Paracelsus, which means greater than Celsus, author of a 1st century medical encyclopediaRejection of Hippocrates theory of health and Galens anatomyMerger of alchemy and medicineThree principles: sulfur, mercury, saltThe poison is the cure

Philippus Aureolus Theophrastus Bombastus von Hohenheim 1493-1541; Switzerland and Austria

German Iatrochemical SchoolJohann Joachim Becher, devised theory of combustion based on phlogiston [from Greek - phlogistn (burning up)]Georg Ernst Stahl, provided experimental support for phlogiston

Becher, 1635-1682, Present-day Germany and England

Stahl, 1659-1734, Present-day GermanyChemistry of Phlogiston

The Study of AirsJoseph Black: fixed air (carbon dioxide)Henry Cavendish: inflammable air (hydrogen)Joseph Priestley: dephlogisticated air (oxygen)

1728-17991731-18101733-1804

Priestley, son of the EnlightenmentDissenting clergymanTheologian and founder of UnitarianismEducator (English Grammar & Chart of History)Political theoristInventor (soda water; erasers)Natural Philosopherelectricitygasses

Antoine-Laurent de LavosierMinor nobility of FranceDegree in law but never practicedEarly work on Geology, chemistry of minerals, and meteorologyBegan the study of combustion and noted that sulfur and phosphorus increased in weight after burningThus, phlogiston would have to have negative weightMet Priestley (1774)Began work on oxygen (1775) and rejected phlogiston theory

Marie-Anne (1758-1836) and Antoine (1743-1794)Elements of Chemistry

Published in 1789Contained 55 substances that could not be decomposed into simpler substances (elements)Statement of conservation of massFirst modern text that defined the science of chemistryLavoisier had offended Marat and had been a member of a tax collecting commissionJudgment of the court: The Republic needs neither scientists nor chemists; the course of justice cannot be delayed. Despite important work on the Gunpowder Commission and his support of the revolution, he was beheaded in May 1794 at age 50.

Humphry DavyLavoisier's theory of elements quickly took overDavy used Voltas pile to decompose substances by electrolysis and discovered magnesium, boron, and bariumChemistry of chlorine and iodineMentor to Michael Faraday

1778-1829Electrolysis of sodium chloride

John DaltonInterpreted the gas laws to mean that elements must exist as atomsReactions are interactions of atomsAtoms combine in whole number ratios (Laws of simple and multiple proportions)Atoms cannot change (Law of constant composition)Atoms have a constant weight; so the total mass of reactants must equal the total mass of product (Law of equivalent weights)

1766-1844System of DaltonWorked to define atomic weights based on Hydrogen = 1

Jns Jacob BerzeliusDefined modern notationSet weight of Oxygen = 100 and other elements relative to thatConfirmed law of simple and multiple proportions and supported Daltons atomic theory

1779-1848, SwedenProblem with Hydrogen SolvedAmadeo Avagadro (1776-1856, Italy) proposed equal volumes of all gasses at the same temperature and pressure contain the same number of moleculesOnly possible if diatomics exist Berzelius adamant: no diatomics possibleDiatomics supported by Stanislao Cannizzaro (1826-1910, Italy)

H + Cl = HClUnless hydrogen and chlorine exist as diatomics, this reaction should produce only one volume of HCl.SpectroscopyRobert Wilhelm Bunsen and Gustav Robert Kirchhoff (Germany)Spectroscope (1859)Used spectral signatures to search for new elements

Kirchhoff (1824-1887); Bunsen (1811-1899)Discovery of HeliumAugust 18, 1868; unusual spectral line detected in solar chromosphere during a solar eclipse

Periodic LawsThe elements seemed to have repeating or periodic properties according to molecular weightsThus, elements appeared to occur in families like the halogens: Fluorine, Chlorine, Bromine, Iodine, all of which have similar combining propertiesDevelopment of Periodic LawsIndependently defined and formalized into tabular form by Dimitri Ivanovich Mendeleev (1869) and Julius Lothar Meyer (1870)

Meyer, 1830-1895, GermanyMendeleev, 1834-1907, Russian EmpireDiscovery of the electronSir Joseph John (J. J.) Thomson (1856-1940)

Discovery of the NucleusErnest Rutherford, 1st Baron Rutherford of Nelson (1871-1937; New Zealand, Canada, and Britain)

The Bohr AtomNiels Henrik David Bohr (1885-1962; Denmark)

Electron Shells

Glen SeaborgDiscoverer of plutonium and 9 other transuranium elementsRemoved the rare earths to make the table more compactAdvisor to presidents from Truman to ClintonFormer head of the AEC

1912-1999, USA

Element Song plus AristotleTom Lehrernull102167.055