Copyright© by Houghton Mifflin Company. All rights reserved. Atomic Structure.
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Copyright by Houghton Mifflin Company. All rights reserved.Atomic Structure
*Composition of the Atom
*An atom viewed in cross section.
*It takes 190,000,000 copper atoms to span the diameter of a penny!!!!!
*Is it possible that there is no God?Consider the following logic:The universe had a beginningAll things that begin need a beginnerTherefore, the universe had a beginner
It is inescapable that something created the universe!We call that something GodGiven what we know about the universe, God is immensely powerful!
*AtomSmallest particle of an element that retains the chemical identity of the element
Remember: elements are pure substances
*Atomic MicroscopyScanning Electron Microscope--SEMGold Atomic Structure5nmSilicon Atoms
Atomic Diameter= 0.234nm
*Daltons Atomic Theory of Matter
Each element composed of tiny particles called atomsAll atoms of a given element are identicalbut different from all othersAtoms cannot be subdivided, created, or destroyed in chemical reactionsAtoms of different elements combine in simple whole number ratios to form compoundsIn chemical reactions, atoms are combined, separated, or rearranged.
*Greeks Through the 1700sDemocritus 450 BCAll matter composed of atomosAristotle disagreed:What holds these atomos together?
LavoisierLaw of Conservation of MatterProustLaw of constant compositionCompounds have same proportions by mass
*Discovering Atomic StructureFranklin1706-1790Kite in a thunderstorm storyConcluded that objects have two kinds of charge: + - (like repel)Lightning is static electricity on a large scaleWhere do charges come from?Faraday1839 Atomic structure related to electricityElectricity comes from Greek elektronAfter many experimentsAtoms contain particles that have electric charge
*Sub Atomic ParticlesMuch of Daltons theory is still accepted todayException:Atoms are divisible into subatomic particlesProtonsNeutronsElectronsIn 1897 English physicist J. J. Thompson discovered the electronElectrons are negatively charged particles.
*Cathode Ray TubeThompson used the CRT to investigate electrons
*Thompson modified the CRT as shown belowA paddle wheel was placed in the stream of electrons. The electron beam made the wheel spin leading to the conclusion that electrons have mass.
*J. J. Thompson (1856-1940)In 1896 . . .Thompson modified the CRTConcluded: cathode ray composed of negatively charged particles1.76 x 10 8 Coulombs/gramThompson concluded that negative particles issued from the cathodeMeant that atoms have a substructureIf there were negative parts of the atom, then there must be positive parts of the atom because atoms are normally neutral
*Mass of an ElectronThompson was not able to determine charge of single electronMillikans oil drop experiment did thatMilikan determinedCharge of electron = 1.60 x 10-19 coulombsMass of electron = 9.11 x 10-28 grams Mass of electron = 9.109 x 10-31kg1/2000th the mass of a hydrogen atom
*Thompson Plum Pudding model of an atom.
*Properties of Subatomic Particles
*Rutherfords experiment circa 1909(alpha scattering experiment)1/8000 alpha particle were deflectedLike a Toyota hitting a Mack truck!!Rutherford had discovered the nucleus
*Alpha particles scattered from the gold foil
*Result of Rutherford Gold Foil Experiment
*Results of foil experiment if Plum Pudding model had been correct.
*Modern Atomic TheoryAtoms composed of protons, neutrons and electrons. Protons and neutrons form the nucleusElectrons move in the space outside the nucleusAtomic number = number of protonsIons are atoms with a chargeIonic charge = #protons - #electronsIsotopes are atoms with the same number of protons but different number of neutronsHydrogen-1protiumHydrogen-2 deuteriumHydrogen-3Tritium
*Figure 3.10: Two isotopes of sodium.Mass # SymbolAtomic #Mass # = Atomic # + # neutrons
27 3+79 2- Al Se1334
#protons = ?#neutrons = ?# electrons = ?
*Atomic MassThe atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element.A weighted average mass reflects both the mass and the relative abundance of the isotopes as they occur in nature.
*AMU1/12 mass of a carbon atom = 1.66 x 10-24g =1amuChlorine-3534.969 AMU
Atomic mass on periodic table is really average atomic mass in AMUsFor ChlorineAtomic Mass =.7577 x 34.969 + .2223 x 36.966 = 35.453 Chlorine 35 Chlorine 37
*Periodic TableA periodic table is an arrangement of elements in Which the elements are separated into groups based on a set of repeating properties.
*Nuclear StabilityNucleus held together by strong nuclear forcesOccur for objects very close togetherNeutrons are glueProvide SNF without repulsion
*Belt of Stability# protons (atomic #)#neutronsMore than one neutrons for everyproton
One proton for every neutron
Atomic # = 20
*Radioactive ParticlesErnest Rutherford (1871-1937)In early 1900s experimented with radioactive materialsChargeName Penetrating Ability-particle2+alpha stopped by paper-particle1-beta stopped by foil/clothes-raynonegamma stopped by lead
*Radioactive ParticlesComposition-particlehelium nuclei (2 protons & 2 Neutrons)-particleelectron-ray high energy radiation
*Radioactive DecayAlpha Decay
*The Positively Charged NucleusHenry Mosely (1887-1915)Every element contains a unique positive charge in its nucleus
*The Periodic Table.
*The ions formed by selected members of groups 1, 2, 3, 6, and 7.Ionic Charge = Atomic Number - # electrons
*Antares is the 15th brightest star in the sky.
It is more than 1000 light years away!
****Chlorine is a reactive element used to disinfect swimming pools. Chlorine occurs as two isotopes: chlorine-35 and chlorine-37. Because there is more chlorine-35 than chlorine-37, the atomic mass of chlorine, 35.453 amu, is closer to 35 than to 37. Evaluating How does a weighted average differ from an arithmetic mean?