Notes: The word fundamental particles denotes atoms or molecules. In element it denotes atoms, while in compounds it denotes molecules.
ATOMIC STRUCTUREATOMIC STRUCTURELearning objectives:Learning objectives:1.1. To know about the fundamental particles of matter.To know about the fundamental particles of matter.2.2. To know about the subatomic particles.To know about the subatomic particles.3.3. To know about the classical and modernTo know about the classical and modernpostulates and theories about the structure ofpostulates and theories about the structure ofatom.atom.
1.1 Introduction1.1 IntroductionThe Three states of matterThe Three states of matterMattersGases SolidsLiquids
1.2 The difference between the1.2 The difference between theThree states of matterThree states of matter1.1. In gases the fundamental particlesIn gases the fundamental particlesare found to be most loosely heldare found to be most loosely helddue to the presence of very weakdue to the presence of very weakforce of attractionforce of attraction2.2. In liquids the fundamental particlesIn liquids the fundamental particlesare found to be loosely held due toare found to be loosely held due tothe presence of some weak force ofthe presence of some weak force ofattraction.attraction.3. In solids the fundamental particles3. In solids the fundamental particlesare found to be tightly held due toare found to be tightly held due tothe presence some strong force ofthe presence some strong force ofattraction.attraction.Note:The word fundamental particles denotes atoms or molecules. In element it denotesatoms, while in compounds it denotes molecules.LiquidsLiquidsGasesGasesSolidsSolids
1.3 What are the fundamental1.3 What are the fundamentalparticles of matter (atoms)?particles of matter (atoms)? An atom is the smallest fundamentalAn atom is the smallest fundamentalparticle of an element that can existparticle of an element that can existindependently and retain all itsindependently and retain all itschemical properties.chemical properties. In other words atoms are buildingIn other words atoms are buildingblocks of all the three forms of theblocks of all the three forms of thematters.matters.Democritus
1.4 Four Element Theory1.4 Four Element Theory Plato was an atomistPlato was an atomist Thought all matter wasThought all matter wascomposed of 4composed of 4elements:elements:– Earth (cool, heavy)Earth (cool, heavy)– Water (wet)Water (wet)– Fire (hot)Fire (hot)– Air (light)Air (light)– Ether (close to heaven)Ether (close to heaven)‘MATTER’FIREEARTHAIRWATERHotWetColdDryRelation of the four elements and the four qualitiesplato
AnaxagorasAnaxagoras (Greek, born 500 B.C.)–Suggested every substance had its own kind of “seedsseeds” that clustered together tomake the substance, much as our atoms cluster to make molecules.1.6 Some Early Ideas on Matter1.6 Some Early Ideas on MatterEmpedoclesEmpedocles (Greek, born in Sicily, 490 B.C.)–Suggested there were only four basic seeds – earth, air, fire, and water– earth, air, fire, and water. Theelementary substances (atoms to us) combined in various ways to makeeverything.DemocritusDemocritus (Thracian, born 470 B.C.)–Actually proposed the word atomproposed the word atom (indivisible) because he believed that allmatter consisted of such tiny units with voids between, an idea quite similar toour own beliefs. It was rejected by Aristotle and thus lost for 2000 years.AristotleAristotle (Greek, born 384 B.C.)–Added the idea of “qualities” – heat, cold, dryness, moisture – as basic elements– heat, cold, dryness, moisture – as basic elementswhich combined as shown in the diagram (previous page).Hot + dry made fire; hot + wet made air, and so on.
The GreeksThe GreeksHistory of the AtomHistory of the Atom Not the history of atom,Not the history of atom,but the idea of the atombut the idea of the atom In 400 B.C the GreeksIn 400 B.C the Greekstried to understandtried to understandmatter (chemicals) andmatter (chemicals) andbroke them down intobroke them down intoearth, wind, fire, and air.earth, wind, fire, and air. Democritus and LeucippusDemocritus and LeucippusGreek philosophersGreek philosophers∼∼LeucippusDemocritus
Greek Model• Greek philosopher• Idea of ‘democracy’• Idea of ‘atomos’– Atom= ‘indivisible’– ‘Atom’ is derived M• No experiments to supportidea• Continuous vs. discontinuoustheory of matterDemocritus’s model of atomNo protons, electrons, or neutronsSolid and INDESTRUCTABLEDemocritus“To understand the very large,we must understand the very small.”
Alchemy• After that chemistry wasruled by alchemy.• They believed that thatcould take any cheapmetals and turn them intogold.• Alchemists were almostlike magicians.– elixirs, physical immortality
Alchemy. . . . .. . . .. . .. ..GOLD SILVER COPPER IRON SANDAlchemical symbols forsubstances…transmutation: changing one substance into anotherIn ordinary chemistry, we cannot transmute elements.∆
1.4 Dalton’s Atomic theoryPostulates of Dalton’s Atomic theory:• All matter consist of tiny particles.• Atoms are indestructible and unchangeable.• Elements are characterized by the mass oftheir atoms• When elements react, their atoms combine insimple numerical ratio.• When elements react their atoms sometimes combine in moresimple wholenumber ratio.John Dalton
Atom1.5 Dalton’s model of the atomA. Atom has nonucleus.B. Atom is solid andIndivisible.
1.5 Thomson model of the atom.(Plum-pudding model)In 1910 William Thomson proposedthe Plum-Pudding model.-- Negative charged electrons wereEmbedded Into a positively chargedelectron cloud.J.J. Thomson+- -- --- -Positively chargednucleusNegatively-chargedelectrons
1.6 Rutherford model of an Atom(The modern view of the atom was developed by Ernest Rutherford)1. In the early twentieth century, Rutherford showed that mostof an atom’s mass is concentrated in small positivelycharged region called the nucleus.2. Atom is almost empty.3. Nucleus has positive charge.4. Electron float around Nucleus.Ernest Rutherford
Bohr model of an atom(planetary model) After Rutherford’s discovery Neils Bohr proposed thatelectrons travel in definite Orbits around the nucleus. Particles in the atom. Electrons- Negative charge. Located out side the nucleus. Proton- positive charge. Located inside the nucleus. Neutron- positive charge Located inside the nucleus.Neils Bohr
Daltons Atomic Theory• Dalton stated thatelements consisted of tinyparticles called atoms• He also called theelements puresubstances because allatoms of an elementwere identical and that inparticular they had thesame mass.