Chapter 2Chapter 2

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

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

definition of element.definition of element. Lavoisier- Father of modern chemistry.Lavoisier- Father of modern chemistry. He wrote the book.He wrote the book.

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

have a constant composition.have a constant composition. The react in specific ratios by mass.The react in specific ratios by mass. Multiple Proportions- When two elements Multiple Proportions- 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 ratios.Small whole number ratios.

ProofProof Mercury has two oxides. One is 96.2 % Mercury has two oxides. One is 96.2 %

mercury by mass, the other is 92.6 % mercury by mass, the other is 92.6 % mercury by mass.mercury by mass.

Show that these compounds follow the law Show that these compounds follow the law of multiple proportion.of multiple proportion.

Speculate on the formula of the two oxides.Speculate on the formula of the two oxides.

Dalton’s Atomic TheoryDalton’s Atomic Theory1)1) Elements are made up of atomsElements are made up of atoms

2)2) Atoms of each element are identical. Atoms of each element are identical. Atoms of different elements are different.Atoms of different elements are different.

3)3) Compounds are formed when atoms 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)4) Chemical reactions are rearrangement of Chemical reactions are rearrangement of atoms. Atoms are not created or atoms. Atoms are not created or destroyed.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 particles.particles.

(called (called Avagadro’s HypothesisAvagadro’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

Voltage source

Thomson’s ExperimentThomson’s Experiment

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

+

-

Thomsom’s ModelThomsom’s Model Found the electron.Found the electron. Couldn’t find positive Couldn’t find positive

(for a while). (for a while). Said the atom was like Said the atom was like

plum pudding.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

Some drops would hoverFrom the mass of the drop and the charge on the plates, he calculated the mass of an electron

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

drilling hole in lead block.drilling 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 thin.atoms 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 pieceat center.at center.

Alpha particlesAlpha particlesare 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 space.empty space. Two regionsTwo regions Nucleus- protons Nucleus- protons

and neutrons.and neutrons. Electron cloud- Electron cloud-

region where you region where you might find an might find an electron.electron.

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

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

neutrons.neutrons. Number of protons = number of electrons if Number of protons = number of electrons if

neutral.neutral.

SymbolsSymbols

XA

Z

Na23

11

Chemical BondsChemical Bonds The forces that hold atoms together.The forces that hold atoms together. Covalent bonding - sharing electrons.Covalent bonding - sharing electrons. Makes molecules.Makes 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

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

Ball and stick.Ball and stick.

IonsIons Atoms or groups of atoms with a charge.Atoms 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 charges.opposite charges. Ionic solids are called salts.Ionic solids are called salts.

Polyatomic IonsPolyatomic Ions Groups of atoms that have a charge.Groups of atoms that have a charge. Yes, you have to memorize them.Yes, you have to memorize them. List on page 66List on page 66

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-metals.non-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 it.If 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 Practice.Practice.

Covalent compoundsCovalent compounds Two words, with prefixes.Two 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 mono.appropriate prefix, except mono. Second element, Second element, -ide -ide ending with ending with

appropriate prefix.appropriate prefix. 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, hepta, mono, di, tri, tetra, penta, hexa, hepta,

octa,nona, decaocta,nona, deca 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 appropriate ending with appropriate

prefixprefix 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 covalent.If it is a non-metal use covalent.

Ionic FormulasIonic Formulas Charges must add up to zero.Charges must add up to zero. Get charges from periodic table, name of Get charges from periodic table, name of

metal ion, or memorized from the list.metal ion, or memorized from the list. Use parenthesis to indicate multiple Use parenthesis to indicate multiple

polyatomics.polyatomics. Use the criss-cross method - it works!!Use the criss-cross method - it works!!

Ionic CompoundsIonic Compounds Sodium sulfideSodium sulfide 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 prefixes in the name tell you how to The prefixes in the name tell you how to

write the formulawrite the formula Sulfur dioxideSulfur dioxide diflourine monoxidediflourine monoxide nitrogen trichloridenitrogen trichloride diphosphorus pentoxidediphosphorus pentoxide

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

dissolved in water.dissolved in water. All acids begin with H.All acids begin with H. Two types of acids: Two types of acids: OxyacidsOxyacids Binary acids and non-oxyacidsBinary acids and non-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 names.Backwards 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 crystals.form 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 trapped.trapped.

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