Chapter 2Chapter 2

Atoms, Molecules, and Ions Atoms, Molecules, and Ions

HistoryHistory GreeksGreeks Democritus and Leucippus - atomosDemocritus and Leucippus - atomos Aristotle- elementsAristotle- elements AlchemyAlchemy 1660 - Robert Boyle- experimental 1660 - Robert Boyle- experimental

definition of element.definition of element. Lavoisier- Father of modern chemistryLavoisier- Father of modern chemistry He wrote the book- used measurementHe wrote the book- used measurement

LawsLaws Conservation of MassConservation of Mass Law of Definite Proportion-Law of Definite Proportion- compounds compounds

have a constant composition by mass.have a constant composition by mass. They react in specific ratios by mass.They react in specific ratios by mass. Multiple Proportions-Multiple Proportions- When two elements When two elements

form more than one compound, the ratios of form more than one compound, the ratios of the masses of the second element that the masses of the second element that combine with one gram of the first can be combine with one gram of the first can be reduced to small whole numbers.reduced to small whole numbers.

What?!What?! Water has 8 g of oxygen per g of hydrogen.Water has 8 g of oxygen per g of hydrogen. Hydrogen peroxide has 16 g of oxygen per Hydrogen peroxide has 16 g of oxygen per

g of hydrogen.g of hydrogen. 16/8 = 2/116/8 = 2/1 Small whole number ratiosSmall whole number ratios

Dalton’s Atomic TheoryDalton’s Atomic Theory 1. Elements are made up of atoms1. Elements are made up of atoms 2. Atoms of each element are identical. 2. Atoms of each element are identical.

Atoms of different elements are different.Atoms of different elements are different. 3. Compounds are formed when atoms 3. Compounds are formed when atoms

combine. Each compound has a specific combine. Each compound has a specific number and kinds of atom.number and kinds of atom.

4. Chemical reactions are rearrangement of 4. Chemical reactions are rearrangement of atoms. Atoms are not created or destroyed.atoms. Atoms are not created or destroyed.

Gay-Lussac- under the same conditions of Gay-Lussac- under the same conditions of temperature and pressure, compounds temperature and pressure, compounds always react in whole number ratios by always react in whole number ratios by volume.volume.

Avagadro- interpreted that to mean Avagadro- interpreted that to mean at the same temperature and pressure, equal at the same temperature and pressure, equal

volumes of gas contain the same number of volumes of gas contain the same number of particlesparticles

(called Avagadro’s hypothesis)(called Avagadro’s hypothesis)

A Helpful ObservationA Helpful Observation

Experiments to determine what Experiments to determine what an atom wasan atom was

J. J. Thomson- used Cathode ray tubesJ. J. Thomson- used Cathode ray tubes

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field he found that the By adding an electric field he found that the moving pieces were negative moving pieces were negative

+

-

Thomsom’s ModelThomsom’s Model Found the electronFound the electron Couldn’t find Couldn’t find

positive (for a while) positive (for a while) Said the atom was Said the atom was

like plum puddinglike plum pudding A bunch of positive A bunch of positive

stuff, with the stuff, with the electrons able to be electrons able to be removed removed

Millikan’s ExperimentMillikan’s Experiment

Atomizer

Microscope

-

+

Oil

Millikan’s ExperimentMillikan’s Experiment

Oil

Atomizer

Microscope

-

+

Oil droplets

Millikan’s ExperimentMillikan’s Experiment

X-rays

X-rays give some drops a charge by knocking offelectrons

Millikan’s ExperimentMillikan’s Experiment

+

Millikan’s ExperimentMillikan’s Experiment

They put an electric charge on the plates

++

--

Millikan’s ExperimentMillikan’s Experiment

Some drops would hover

++

--

Millikan’s ExperimentMillikan’s Experiment

+

+ + + + + + +

- - - - - - -

Millikan’s ExperimentMillikan’s Experiment

Measure the drop and find volume from 4/3πr3

Find mass from M = D x V

++

--

Millikan’s ExperimentMillikan’s Experiment

From the mass of the drop and the charge on the plates, he calculated the charge on an electron

++

--

RadioactivityRadioactivity Discovered by accidentDiscovered by accident BequerelBequerel Three types Three types

– alpha- helium nucleus (+2 charge, large alpha- helium nucleus (+2 charge, large mass)mass)

– beta- high speed electronbeta- high speed electron

– gamma- high energy lightgamma- high energy light

Rutherford’s ExperimentRutherford’s Experiment Used uranium to produce alpha particlesUsed uranium to produce alpha particles Aimed alpha particles at gold foil by Aimed alpha particles at gold foil by

drilling hole in lead blockdrilling hole in lead block Since the mass is evenly distributed in Since the mass is evenly distributed in

gold atoms alpha particles should go gold atoms alpha particles should go straight through.straight through.

Used gold foil because it could be made Used gold foil because it could be made atoms thinatoms thin

Lead block

Uranium

Gold Foil

Florescent Screen

What he expected

Because

Because, he thought the mass was evenly distributed in the atom

What he got

How he explained it

+

Atom is mostly emptyAtom is mostly empty Small dense,Small dense,

positive piecepositive piece at centerat center

Alpha particles Alpha particles are deflected byare deflected by it if it if they get closethey get close enough enough

+

Modern ViewModern View The atom is mostly The atom is mostly

empty spaceempty space Two regionsTwo regions Nucleus- protons and Nucleus- protons and

neutronsneutrons Electron cloud- region Electron cloud- region

where you have a where you have a chance of finding an chance of finding an electronelectron

Sub-atomic ParticlesSub-atomic Particles Z - atomic number = number of protons Z - atomic number = number of protons

determines type of atomdetermines type of atom A - mass number = number of protons + A - mass number = number of protons +

neutronsneutrons Number of protons = number of electrons if Number of protons = number of electrons if

neutralneutral

SymbolsSymbols

XA

Z

Na23

11

Chemical BondsChemical Bonds The forces that hold atoms togetherThe forces that hold atoms together Covalent bonding - sharing electronsCovalent bonding - sharing electrons makes moleculesmakes molecules Chemical formula- the number and type of Chemical formula- the number and type of

atoms in a molecule atoms in a molecule

CC22HH66 - 2 carbon atoms, 6 hydrogen atoms, - 2 carbon atoms, 6 hydrogen atoms,

Structural formula shows the connections, Structural formula shows the connections, but not necessarily the shape.but not necessarily the shape.

H

H

H H

H

HC C

Structural FormulaStructural Formula

There are also other model that attempt to There are also other model that attempt to show three dimensional shapeshow three dimensional shape

Ball and stick (see the models in room)Ball and stick (see the models in room)

Space Filling Space Filling

IonsIons Atoms or groups of atoms with a chargeAtoms or groups of atoms with a charge Cations- positive ions - get by losing Cations- positive ions - get by losing

electrons(s)electrons(s) Anions- negative ions - get by gaining Anions- negative ions - get by gaining

electron(s)electron(s) Ionic bonding- held together by the Ionic bonding- held together by the

opposite chargesopposite charges Ionic solids are called saltsIonic solids are called salts

Polyatomic Ions Polyatomic Ions Groups of atoms that have a chargeGroups of atoms that have a charge Yes, you have to memorize them.Yes, you have to memorize them. List on page 65List on page 65

Periodic TablePeriodic Table

MetalsMetals ConductorsConductors Lose electronsLose electrons Malleable and ductileMalleable and ductile

NonmetalsNonmetals BrittleBrittle Gain electronsGain electrons Covalent bondsCovalent bonds

Semi-metals or MetalloidsSemi-metals or Metalloids

Alkali Metals

Alkaline Earth Metals

Halogens

Transition metals

Noble Gases

Inner Transition Metals

+1+2 -1-2-3

Naming compoundsNaming compounds Two typesTwo types IonicIonic - metal and non metal or polyatomics - metal and non metal or polyatomics CovalentCovalent- we will just learn the rules for 2 - we will just learn the rules for 2

non-metalsnon-metals

Ionic compoundsIonic compounds If the cation is monoatomic- Name the If the cation is monoatomic- Name the

metal (cation) just write the name.metal (cation) just write the name. If the cation is polyatomic- name itIf the cation is polyatomic- name it If the anion is monoatomic- name it but If the anion is monoatomic- name it but

change the ending to change the ending to -ide-ide If the anion is poly atomic- just name itIf the anion is poly atomic- just name it practicepractice

Covalent compoundsCovalent compounds Two words, with prefixesTwo words, with prefixes Prefixes tell you how many.Prefixes tell you how many. mono, di, tri, tetra, penta, hexa, septa, nona, mono, di, tri, tetra, penta, hexa, septa, nona,

decadeca First element whole name with the First element whole name with the

appropriate prefix, except monoappropriate prefix, except mono Second element, Second element, -ide -ide ending with ending with

appropriate prefixappropriate prefix PracticePractice

More NamingMore Naming

Ionic compoundsIonic compounds If the cation is monoatomic- Name the If the cation is monoatomic- Name the

metal (cation) just write the name.metal (cation) just write the name. If the cation is polyatomic- name itIf the cation is polyatomic- name it If the anion is monoatomic- name it but If the anion is monoatomic- name it but

change the ending to change the ending to -ide-ide If the anion is poly atomic- just name itIf the anion is poly atomic- just name it practicepractice

Ionic CompoundsIonic Compounds Have to know what ions they formHave to know what ions they form off table, polyatomic, or figure it outoff table, polyatomic, or figure it out CaSCaS

KK22SS

AlPOAlPO44

KK22SOSO44

FeSFeS

CoICoI33

Ionic CompoundsIonic Compounds FeFe22(C(C22OO44))

MgOMgO

MnOMnO

KMnOKMnO44

NHNH44NONO33

HgHg22ClCl22

CrCr22OO33

Ionic CompoundsIonic Compounds KClOKClO44

NaClONaClO33

YBrOYBrO22

Cr(ClO)Cr(ClO)66

Naming Covalent CompoundsNaming Covalent Compounds Two words, with prefixesTwo words, with prefixes Prefixes tell you how many.Prefixes tell you how many. mono, di, tri, tetra, penta, hexa, septa, nona, mono, di, tri, tetra, penta, hexa, septa, nona,

decadeca First element whole name with the First element whole name with the

appropriate prefix, except monoappropriate prefix, except mono Second element, Second element, -ide -ide ending with ending with

appropriate prefixappropriate prefix PracticePractice

COCO22

CO CO

CClCCl44

NN22OO44

XeFXeF66

NN44OO44

PP22OO1010

Naming Covalent CompoundsNaming Covalent Compounds

Writing FormulasWriting Formulas Two sets of rules, ionic and covalentTwo sets of rules, ionic and covalent To decide which to use, decide what the To decide which to use, decide what the

first word is.first word is. If is a metal or polyatomic use ionic.If is a metal or polyatomic use ionic. If it is a non-metal use covalentIf it is a non-metal use covalent

Ionic FormulasIonic Formulas Charges must add up to zeroCharges must add up to zero get charges from table, name of metal ion, get charges from table, name of metal ion,

or memorized from the listor memorized from the list use parenthesis to indicate multiple use parenthesis to indicate multiple

polyatomicspolyatomics

Ionic FormulasIonic Formulas Sodium nitrideSodium nitride sodium- Na is always +1sodium- Na is always +1 nitride - ide tells you it comes from the nitride - ide tells you it comes from the

tabletable

nitride is Nnitride is N-3-3

Ionic FormulasIonic Formulas Sodium nitrideSodium nitride sodium- Na is always +1sodium- Na is always +1 nitride - ide tells you it comes from the nitride - ide tells you it comes from the

tabletable

nitride is Nnitride is N-3-3 doesn’t add up to zerodoesn’t add up to zero

Na+1 N-3

Ionic FormulasIonic Formulas Sodium nitrideSodium nitride sodium- Na is always +1sodium- Na is always +1 nitride - ide tells you it comes from the nitride - ide tells you it comes from the

tabletable

nitride is Nnitride is N-3-3 doesn’t add up to zerodoesn’t add up to zero Need 3 NaNeed 3 NaNa+1 N-3 Na3N

Ionic CompoundsIonic Compounds Sodium sulfiteSodium sulfite calcium iodidecalcium iodide Lead (II) oxide Lead (II) oxide Lead (IV) oxideLead (IV) oxide Mercury (I) sulfideMercury (I) sulfide Barium chromateBarium chromate Aluminum hydrogen sulfateAluminum hydrogen sulfate Cerium (IV) nitriteCerium (IV) nitrite

Covalent compoundsCovalent compounds The name tells you how to write the The name tells you how to write the

formulaformula duhduh Sulfur dioxideSulfur dioxide diflourine monoxidediflourine monoxide nitrogen trichloridenitrogen trichloride diphosphorus pentoxidediphosphorus pentoxide

More Names and formulasMore Names and formulas

AcidsAcids Substances that produce HSubstances that produce H++ ions when ions when

dissolved in waterdissolved in water All acids begin with HAll acids begin with H Two types of acids Two types of acids OxyacidsOxyacids non oxyacidsnon oxyacids

Naming acidsNaming acids If the formula has oxygen in itIf the formula has oxygen in it write the name of the anion, but change write the name of the anion, but change

– ate to -ic acidate to -ic acid

– ite to -ous acidite to -ous acid Watch out for sulfWatch out for sulfururic and sulfic and sulfururousous

HH22CrOCrO44

HMnOHMnO44

HNOHNO22

Naming acidsNaming acids If the acid doesn’t have oxygenIf the acid doesn’t have oxygen add the prefix hydro-add the prefix hydro- change the suffix -ide to -ic acidchange the suffix -ide to -ic acid HClHCl

HH22SS

HCNHCN

Formulas for acidsFormulas for acids Backwards from namesBackwards from names If it has hydro- in the name it has no oxygenIf it has hydro- in the name it has no oxygen anion ends in -ideanion ends in -ide No hydro, anion ends in -ate or -iteNo hydro, anion ends in -ate or -ite Write anion and add enough H to balance Write anion and add enough H to balance

the charges.the charges.

Formulas for acidsFormulas for acids hydrofluoric acidhydrofluoric acid dichromic aciddichromic acid carbonic acidcarbonic acid hydrophosphoric acidhydrophosphoric acid hypofluorous acidhypofluorous acid perchloric acidperchloric acid phosphorous acid phosphorous acid

HydratesHydrates Some salts trap water crystals when they Some salts trap water crystals when they

form crystalsform crystals these are hydrates.these are hydrates. Both the name and the formula needs to Both the name and the formula needs to

indicate how many water molecules are indicate how many water molecules are trappedtrapped

In the name we add the word hydrate with a In the name we add the word hydrate with a prefix that tells us how many water prefix that tells us how many water molecules molecules

HydratesHydrates In the formula you put a dot and then write In the formula you put a dot and then write

the number of molecules.the number of molecules.

Calcium chloride dihydrate = CaClCalcium chloride dihydrate = CaCl2222 Chromium (III) nitrate hexahydrate = Chromium (III) nitrate hexahydrate =

Cr(NOCr(NO33))33 6H 6H22O O