Presentation on theme: "CHAPTER 3 Atoms: The Building Blocks of Matter"— Presentation transcript:
1 CHAPTER 3 Atoms: The Building Blocks of Matter CHEMISTRY
2 Foundations of Atomic Theory HistoryGreekDemocritus – “atom” – could not be divided anymoreAristotle and Plato - arguedsNatural PhilosophersExperimentation – balances – quantitative measurementsAtomComes from Greek“a” – not“tomos” – cuttingindivisible
3 Foundations of Atomic Theory Chemical ReactionTransformation of substances into one or more new substancesChemical changeLaw of Conservation of MassMass is neither created nor destroyed in ordinary chemical reactionsLaw of Definite ProportionsA chemical compound contains the same elements in exactly the same proportions by mass regardless of size of sampleEx – H2O, CO2
4 Foundations of Atomic Theory Law of Multiple ProportionsIf two or more compounds are composed of the same 2 elements, the masses can be expressed as ratios of small whole numbers
5 Dalton’s Atomic Theory John DaltonEnglish School Teacher1803
6 Dalton’s Atomic Theory 5 Points in his theoryAll matter is composed of extremely small particles called atomsAtoms of a given element are identical in size, mass, and other propertiesAtoms cannot be subdivided, created, or destroyedAtoms of different elements combine in simple whole number ratios to form compoundsIn chemical reactions, atoms are combined, separated, or rearranged
8 Modern Atomic TheoryThere have been some changes since Dalton’s TheoryImportant concepts of modern theoryAll matter is composed of atomsAtoms of one element differ in properties from atoms of another element
9 Structure of the AtomAtom – smallest particle of an element that can exist aloneTwo regions of an atomNucleusCenter of atomProtons and neutronsElectron “cloud”Area surrounding nucleuscontaining electrons
10 Discovery of the electron Symbol e-Cathode ray tubesVacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to form images in the form of light emitted from the fluorescent screen.Used in TV, computer monitors
11 Discovery of the electron Charge and mass of the electronJJ Thomson – 1897Discovered the electron1907 Nobel Prize in PhysicsDid experiments with CRT –Found that the charge to massration was always the same
12 Discovery of the atomic nucleus Ernest Rutherford – 1908Gold Foil Experiment
13 Composition of the nucleus ProtonsPositive chargeNeutronsNeutral charge
14 Forces in Nucleus Nuclear forces Forces that hold nuclear particles togetherBinds protons and neutrons into the atomic nucleus
17 Counting Atoms Atomic Number Symbol Z Number of protons in nucleus The number of protons determines identity of the element!!
18 Counting Atoms Isotopes Atoms of the same element with varying number of neutronsNuclide – general term for any isotope of any elementMass Number – total number of protons + neutrons
19 Counting Atoms The isotope of hydrogen Protium – one proton only; 1e- Deuterium – one proton, one neutron, one electronTritium – one proton, two neutrons, one electron; radioactive
20 Counting Atoms Designating Isotopes Hyphen notation Name-mass #Uranium-235Ex – Neon with 12 neutrons?Nuclear Symbol NotationMNAN Element symbol31H23592UHow many p,n,e- in chlorine-37?
21 Relative Atomic Mass Relative scale Atomic mass unit Standard Way to compareCarbon-12All others compared to Carbon-12Atomic mass unitamuApproximate mass of a proton or a neutron
22 Average Atomic MassWeighted average of the atomic masses for all known isotopesCalculating average atomic mass:
23 Relating mass to the number of atoms “Particle” – a generic termMole – SI unit for amount of substance, counting unitSymbol – molAvogadro’s number6.02 x 1023 – number of particles in 1mol of substanceMolar massMass of 1mol of substance = atomic mass
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