Chapter 2

Atoms, Molecules, and Ions

HistoryHistory

GreeksGreeks Democritus and Leucippus – atomos Democritus and Leucippus – atomos

(meaning indivisible or uncuttable) (meaning indivisible or uncuttable) Aristotle- elementsAristotle- elements Alchemy (a Alchemy (a phase in the development

of modern chemistry) English schoolteacher, John Dalton English schoolteacher, John Dalton

linked the idea of elements with the linked the idea of elements with the idea of atoms. 1803-1807idea of atoms. 1803-1807

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

Laws

Conservation of Mass Law of Definite Proportion-

compounds have a constant composition by mass.

They react in specific ratios by mass.

Experiments to determine what an atom was

J. J. Thomson- used Cathode ray tubes Thomson’s experiment (1897) is

generally accepted as the discovery of the electron.

Thomson’s ExperimentVoltage source

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Thomson’s ExperimentVoltage source

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Thomson’s ExperimentThomson’s ExperimentVoltage source

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

Thomson’s ExperimentThomson’s ExperimentVoltage source

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

Thomson’s ExperimentThomson’s ExperimentVoltage source

+-

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

Thomson’s ExperimentThomson’s ExperimentVoltage source

+-

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

Thomson’s ExperimentThomson’s ExperimentVoltage source

+-

Voltage source

Thomson’s Experiment

By adding an electric field

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

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

+

-

Thomsom’s Model

Found the electron Couldn’t find

positive (for a while)

Said the atom was like plum pudding

A bunch of positive stuff, with the electrons able to be removed

RadioactivityDiscovered by accident by Henri BequerelThree types alpha- do not travel very far, do not pass through anything thick (less than 1in), can be very damaging when inside the body, but outside particles won’t even go through the skinbeta- high speed electron, can travel up to six feet from source, like alpha more damaging inside the human body than outsideGamma (x rays)- high energy light (photons), travel the speed of light, have greater penetrating power than alpha or beta, gamma rays come from the nucleus while x rays come from electron shells,

Rutherford’s Experiment

Used uranium to produce alpha particles

Aimed alpha particles at gold foil by drilling hole in lead block

Since the mass is evenly distributed in gold atoms alpha particles should go straight through.

Used gold foil because it could be made thin

Lead block

Uranium

Gold Foil

Florescent Screen

What he expected

Because the current model suggested:

Because, he thought the mass was evenly distributed

What he got

How he explained it

+

Atom is mostly emptyAtom is mostly empty Small dense, positive piece at centerSmall dense, positive piece at center Alpha particles Alpha particles

are deflected by it if they get close are deflected by it if they get close enoughenough

+

Modern ViewModern View

The atom is mostly The atom is mostly empty spaceempty space

Two regionsTwo regions Nucleus- protons Nucleus- protons

and neutronsand neutrons Electron cloud- Electron cloud-

region where you region where you have a chance of have a chance of finding an electronfinding an electron

Sub-atomic ParticlesSub-atomic Particles

Z - atomic number = number of Z - atomic number = number of protons determines type of atomprotons determines type of atom

A - mass number = number of A - mass number = number of protons + neutronsprotons + neutrons

Number of protons = number of Number of protons = number of electrons if neutralelectrons if neutral

SymbolsSymbols

XA

Z

Na23

11

Atomic mass number

Atomic number

IonsIons

Atoms or groups of atoms with a Atoms or groups of atoms with a chargecharge

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

Ions Ions

A polyatomic ion are groups of atoms that have a chargeA polyatomic ion are groups of atoms that have a charge

Chemical symbol for ionsChemical symbol for ions

XA ± #

Atomic mass number

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

Alkaline Earth Metals

Alkaline Earth Metals

Halogens

Transition metals

Noble Gases

Inner Transition Metals

+1+2 -1-2-3

NomenclatureNomenclature

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.

There are also other model that There are also other model that attempt to show three dimensional attempt to show three dimensional shapeshape

Ball and stick Ball and stick

Space Filling Space Filling

Naming compoundsNaming compounds

Two typesTwo types IonicIonic - metal and non metal or - metal and non metal or

polyatomicspolyatomics CovalentCovalent- we will just learn the rules - we will just learn the rules

for 2 non-metalsfor 2 non-metals

Ionic compoundsIonic compounds

Write the cation first. Change the anion’s ending to -ide. Write the names of polyatomic ions. For ions with variable oxidation #’s

(Transition metals, or Tin or Lead), write the oxidation# in parentheses using Roman numerals. Remember the overall charge = 0.

Ionic CompoundsIonic Compounds

Remember you have to know what ions they form off Remember you have to know what ions they form off table, or figure it out!table, or figure it out!CaSCaSKK22SSAlPOAlPO44 KK22SOSO44FeSFeSCoICoI33

Ionic CompoundsIonic Compounds

MgOMgO MnOMnO KMnOKMnO44 NHNH44NONO33 HgHg22ClCl22 CrCr22OO33

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, mono, di, tri, tetra, penta, hexa,

septa or hepta, octa, nona, decasepta or hepta, octa, 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 ending with

appropriate prefixappropriate prefix

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 To decide which to use, decide what

the first element is.the first element 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 get charges from table, name of

metal ion, or memorized from the metal ion, or memorized from the listlist

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 tablenitride - ide tells you it comes from the table nitride is Nnitride is N-3-3 doesn’t add up to zerodoesn’t add up to zero Criss-cross charges to balanceCriss-cross charges to balance

Na+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 difluorine monoxidedifluorine monoxide nitrogen trichloridenitrogen trichloride diphosphorus pentoxidediphosphorus pentoxide

More Names and formulasMore Names and formulas

Acids and HydratesAcids and Hydrates

AcidsAcids

Substances that produce HSubstances that produce H++ ions ions when dissolved in waterwhen dissolved 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 If it has hydro- in the name it has no

oxygenoxygen 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 Write anion and add enough H to

balance the charges.balance 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 Some salts trap water crystals when they form crystalsthey form crystals

these are hydrates.these are hydrates. Both the name and the formula needs Both the name and the formula needs

to indicate how many water molecules to indicate how many water molecules are trappedare trapped

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

HydratesHydrates

In the formula you put a dot and In the formula you put a dot and then write the number of molecules.then write the number of molecules.

Calcium chloride dihydrate = Calcium chloride dihydrate = CaClCaCl2222

Chromium (III) nitrate hexahydrate Chromium (III) nitrate hexahydrate = Cr(NO= Cr(NO33))33 6H 6H22O O