CHAPTER 3 Atoms: The Building Blocks of Matter CHEMISTRY

CHAPTER 3CHAPTER 3Atoms: The Building Blocks of MatterAtoms: The Building Blocks of Matter

CHEMISTRYCHEMISTRY

Foundations of Atomic TheoryFoundations of Atomic Theory

HistoryHistory– GreekGreek

Democritus – “atom” – could not be divided anymoreDemocritus – “atom” – could not be divided anymore Aristotle and Plato - arguedAristotle and Plato - argued

– 1600-1700s1600-1700s Natural PhilosophersNatural Philosophers

– Experimentation – balances – quantitative measurementsExperimentation – balances – quantitative measurements

AtomAtom– Comes from GreekComes from Greek

““a” – nota” – not ““tomos” – cuttingtomos” – cutting indivisibleindivisible

Foundations of Atomic TheoryFoundations of Atomic Theory Chemical ReactionChemical Reaction

– Transformation of substances into one or more Transformation of substances into one or more new substancesnew substances

– Chemical changeChemical change Law of Conservation of MassLaw of Conservation of Mass

– Mass is neither created nor destroyed in Mass is neither created nor destroyed in ordinary chemical reactionsordinary chemical reactions

– http://www.youtube.com/watch?http://www.youtube.com/watch?v=dExpJAECSL8v=dExpJAECSL8

Law of Definite ProportionsLaw of Definite Proportions– A chemical compound contains the same A chemical compound contains the same

elements in exactly the same proportions by elements in exactly the same proportions by mass regardless of size of samplemass regardless of size of sample

– Ex – HEx – H22O, COO, CO22

Foundations of Atomic TheoryFoundations of Atomic Theory

Law of Multiple ProportionsLaw of Multiple Proportions– If two or more compounds are If two or more compounds are

composed of the same 2 elements, the composed of the same 2 elements, the masses can be expressed as ratios of masses can be expressed as ratios of small whole numberssmall whole numbers

Dalton’s Atomic TheoryDalton’s Atomic Theory

John DaltonJohn Dalton English School TeacherEnglish School Teacher 18031803


5 Points in his theory5 Points in his theory– All matter is composed of extremely small All matter is composed of extremely small

particles called atomsparticles called atoms– Atoms of a given element are identical in size, Atoms of a given element are identical in size,

mass, and other propertiesmass, and other properties– Atoms cannot be subdivided, created, or Atoms cannot be subdivided, created, or

destroyeddestroyed– Atoms of different elements combine in simple Atoms of different elements combine in simple

whole number ratios to form compoundswhole number ratios to form compounds– In chemical reactions, atoms are combined, In chemical reactions, atoms are combined,

separated, or rearrangedseparated, or rearranged


Modern Atomic TheoryModern Atomic Theory

There have been some changes since There have been some changes since Dalton’s TheoryDalton’s Theory

Important concepts of modern theoryImportant concepts of modern theory– Atoms of one element can differ from Atoms of one element can differ from

each other - ISOTOPESeach other - ISOTOPES– An atom is made of smaller partsAn atom is made of smaller parts

Structure of the AtomStructure of the Atom

Atom – smallest particle of an element Atom – smallest particle of an element that can exist alone that can exist alone – Two regions of an atomTwo regions of an atom

NucleusNucleus– Center of atomCenter of atom– Protons and neutronsProtons and neutrons

Electron “cloud”Electron “cloud”– Area surrounding nucleus Area surrounding nucleus

containing electronscontaining electrons

Discovery of the electronDiscovery of the electron

Symbol Symbol e e--

Cathode ray tubes (CRT)Cathode ray tubes (CRT)– Vacuum tube containing an electron gun (a source of Vacuum tube containing an electron gun (a source of

electrons) and a fluorescent screen, with internal or external electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to means to accelerate and deflect the electron beam, used to form images in the form of light emitted from the fluorescent form images in the form of light emitted from the fluorescent screen. screen.

– Used in TV, computer monitorsUsed in TV, computer monitors

Discovery of the electronDiscovery of the electron

Charge and mass of the electronCharge and mass of the electron– JJ Thomson – 1897JJ Thomson – 1897

Discovered the electronDiscovered the electron 1907 Nobel Prize in Physics1907 Nobel Prize in Physics http://videos.howstuffworks.com/hsw/6298-atomic-shttp://videos.howstuffworks.com/hsw/6298-atomic-s

tructure-electrons-video.htmtructure-electrons-video.htm Did experiments with CRT – Did experiments with CRT –

– Found that the charge to mass Found that the charge to mass

ration was always the sameration was always the same

Discovery of the atomic nucleusDiscovery of the atomic nucleus

Ernest Rutherford – 1908Ernest Rutherford – 1908 Gold Foil ExperimentGold Foil Experiment

Composition of the nucleusComposition of the nucleus

ProtonsProtons– Positive charge Positive charge

http://videos.howstuffworks.com/hsw/58http://videos.howstuffworks.com/hsw/5806-atomic-structure-the-nucleus-video.h06-atomic-structure-the-nucleus-video.htmtm

NeutronsNeutrons– Neutral chargeNeutral charge

http://videos.howstuffworks.com/hsw/580http://videos.howstuffworks.com/hsw/5807-atomic-structure-neutrons-video.htm7-atomic-structure-neutrons-video.htm

Forces in NucleusForces in Nucleus

Nuclear forcesNuclear forces– Forces that hold nuclear particles Forces that hold nuclear particles

togethertogether– Binds protons and neutrons into the Binds protons and neutrons into the

atomic nucleusatomic nucleus

Sizes of AtomsSizes of Atoms

Based on distance electrons travel away Based on distance electrons travel away from the nucleusfrom the nucleus

http://videos.howstuffworks.com/hsw/5788-http://videos.howstuffworks.com/hsw/5788-size-of-atoms-matter-video.htmsize-of-atoms-matter-video.htm

SummarySummary

Counting AtomsCounting Atoms

Atomic NumberAtomic Number– Symbol Symbol Z Z– Number of protons in nucleusNumber of protons in nucleus– The number of protons determines The number of protons determines

identity of the element!!identity of the element!!


IsotopesIsotopes– Atoms of the same element with varying Atoms of the same element with varying

number of neutronsnumber of neutrons– NuclideNuclide – general term for any isotope of – general term for any isotope of

any elementany element– Mass NumberMass Number – total number of protons – total number of protons

+ neutrons+ neutrons


The isotope of hydrogenThe isotope of hydrogen– ProtiumProtium – one proton only; 1e – one proton only; 1e--

– DeuteriumDeuterium – one proton, one neutron, – one proton, one neutron, one electronone electron

– TritiumTritium – one proton, two neutrons, one – one proton, two neutrons, one electron; radioactiveelectron; radioactive

– http://http://www.citycollegiate.com/isotopesofhydrowww.citycollegiate.com/isotopesofhydrogen.htmgen.htm


Designating IsotopesDesignating Isotopes– Hyphen notationHyphen notation

Name-mass #Name-mass #Uranium-235 – How many p, n, e-?Uranium-235 – How many p, n, e-?Ex – Neon with 12 neutrons?Ex – Neon with 12 neutrons?

– Nuclear Symbol NotationNuclear Symbol Notation MNMN

ANAN Element symbolElement symbol

3311HH

2352359292UU

How many p,n,eHow many p,n,e-- in chlorine-37? in chlorine-37?

Relative Atomic MassRelative Atomic Mass

Relative scaleRelative scale– Standard needed to be setStandard needed to be set– Carbon-12Carbon-12

All others compared to Carbon-12All others compared to Carbon-12 Atomic mass unitAtomic mass unit

– amuamu– The mass of an individual atomThe mass of an individual atom– Honors: Approximate mass of a proton Honors: Approximate mass of a proton

or a neutronor a neutron

Average Atomic MassAverage Atomic Mass

Weighted average of the atomic Weighted average of the atomic masses for all known isotopesmasses for all known isotopes– Calculating average atomic mass:Calculating average atomic mass:

Relating mass to the number of Relating mass to the number of atomsatoms

““Particle” – a generic termParticle” – a generic term Mole – SI unit for amount of Mole – SI unit for amount of

substance, counting unitsubstance, counting unit– Symbol – molSymbol – mol– Avogadro’s numberAvogadro’s number

6.02 x 106.02 x 102323 – number of particles – number of particles

in 1mol of substancein 1mol of substance

– Molar massMolar massMass of 1mol of substance – on P.T.Mass of 1mol of substance – on P.T.

ConversionsConversions

Gram Gram Mole Mole Mole Mole Gram Gram Mole Mole Particle Particle Particle Particle Mole Mole Gram Gram Particle Particle Particle Particle Gram Gram

Facts (Conversion Factors):Facts (Conversion Factors):

#g PT = 1 mol#g PT = 1 mol

6.02 x 106.02 x 102323 particles = 1 mol particles = 1 mol


Gram Gram Mole; Mole Mole; Mole Gram Gram


Mole Mole Particle; Particle Particle; Particle Mole Mole


Gram Gram Particle; Particle Particle; Particle Gram Gram

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CHAPTER 3 Atoms: The Building Blocks of Matter CHEMISTRY