Chapter 2Chapter 2Atoms, Molecules, Atoms, Molecules,

and Ionsand Ions

THE EARLY HISTORY OF THE EARLY HISTORY OF CHEMISTRYCHEMISTRY

Section 2.1Section 2.1

HistoryHistory GreeksGreeks

– Democritus and Leucippos - atomosDemocritus and Leucippos - atomos Aristotle- elementsAristotle- elements AlchemyAlchemy 1660 - Robert Boyle- experimental definition of 1660 - Robert Boyle- experimental definition of

element.element.

– First “chemist”First “chemist” Stahl – combustion and “phlogiston”Stahl – combustion and “phlogiston” Priestley- oxygenPriestley- oxygen

FUNDAMENTAL FUNDAMENTAL CHEMICAL LAWSCHEMICAL LAWS

Section 2.2Section 2.2

Antoine LavoisierAntoine Lavoisier Law of conservation of massLaw of conservation of mass Wrote first modern textbookWrote first modern textbook

– Considered “father of chemistry”Considered “father of chemistry” Executed during French RevolutionExecuted during French Revolution Joseph Proust followed his leadJoseph Proust followed his lead

– Law of definite proportionsLaw of definite proportions John Dalton took all of their work and put it all John Dalton took all of their work and put it all

togethertogether

– Law of multiple proportionsLaw of multiple proportions

LawsLaws Conservation of MassConservation of Mass

– Cannot be created/destroyed (transfer)Cannot be created/destroyed (transfer) Law of Definite Proportion- compounds have a Law of Definite Proportion- compounds have a

constant composition.constant composition.– They react in specific ratios by mass.They react in specific ratios by mass.

Multiple Proportions Multiple Proportions – When two elements form more than one When two elements form more than one

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

DALTON’S ATOMIC DALTON’S ATOMIC THEORYTHEORY

Section 2.3Section 2.3

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.

Atomic massesAtomic masses Dalton put together table of masses for Dalton put together table of masses for

elementselements

– Not always correctNot always correct

– Formulas were wrongFormulas were wrong Gay-LussacGay-Lussac

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

Avogadro - interpreted Gay-Lussac’s idea Avogadro - interpreted Gay-Lussac’s idea to mean: to mean: – at the same temperature and pressure, at the same temperature and pressure,

equal volumes of gas contain the same equal volumes of gas contain the same number of particles.number of particles.

called called Avogadro’s HypothesisAvogadro’s Hypothesis Did not number the exact number yetDid not number the exact number yet Berzelius Berzelius

– Developed modern symbols for elements Developed modern symbols for elements

A Helpful ObservationA Helpful Observation

EARLY EXPERIMENTS TO EARLY EXPERIMENTS TO CHARACTERIZE THE ATOMCHARACTERIZE THE ATOM

Section 2.4Section 2.4

The ElectronThe Electron J. J. ThomsonJ. J. Thomson

– used Cathode ray tubesused Cathode ray tubes

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 end.positive end.

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

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

Oil

Atomizer

Oil droplets

Telescope

-

+

Millikan’s ExperimentMillikan’s Experiment

X-rays

X-rays give some electrons a charge.

Millikan’s ExperimentMillikan’s Experiment

Some drops would hover

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

Fluorescent 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.

+

THE MODERN VIEW OF THE MODERN VIEW OF ATOMIC STRUCTURE: AN ATOMIC STRUCTURE: AN

INTRODUCTIONINTRODUCTION

Section 2.5Section 2.5

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

MOLECULES AND IONSMOLECULES AND IONSSection 2.6Section 2.6

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. CHCH44 - 1 carbon atom, 4 hydrogen atoms, - 1 carbon atom, 4 hydrogen atoms,

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

CH

H

H

H

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

Ball and stick.Ball and stick. Space-fillingSpace-filling

Structural formula

IonsIons Atoms or groups of atoms with a charge.Atoms or groups of atoms with a charge. Cations- positive ions - lose electrons(s).Cations- positive ions - lose electrons(s). Anions- negative ions - gain electron(s).Anions- negative ions - gain electron(s). Ionic bonding- held together by the opposite Ionic bonding- held together by the opposite

charges.charges. Ionic solids are called salts.Ionic solids are called salts. Polyatomic ions - groups of atoms that have a Polyatomic ions - groups of atoms that have a

charge.charge.

Ion ListIon List Yes, you have to memorize them.Yes, you have to memorize them. List from last year – good start!List from last year – good start!

AN INTRODUCTION TO AN INTRODUCTION TO THE PERIODIC TABLETHE PERIODIC TABLE

Section 2.7Section 2.7

PT terminologyPT terminology Groups – columns – families (vertical)Groups – columns – families (vertical)

– Similar chemical propertiesSimilar chemical properties Periods – rows – series (horizontal)Periods – rows – series (horizontal)

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

(or Rare Earth)

+1+2 -1-2-3

NAMING SIMPLE NAMING SIMPLE COMPOUNDSCOMPOUNDS

Section 2.8Section 2.8

Naming compoundsNaming compounds Two typesTwo types IonicIonic - metal and non metal or polyatomic - metal and non metal or polyatomic

ions.ions. 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 metal If the cation is monoatomic- Name the metal

(cation) just write the name.(cation) just write the name.

– Don’t forget Roman numerals if neededDon’t forget Roman numerals if needed If the cation is polyatomic- name it.If the cation is polyatomic- name it. If the anion is monatomic- name it but change If the anion is monatomic- name it but change

the ending to the ending to –ide.–ide. If the anion is polyatomic- just name itIf the anion is polyatomic- just name it

MUST KNOW YOUR IONS!!!!!MUST KNOW YOUR IONS!!!!!

Covalent compoundsCovalent compounds Two words, with prefixes.Two words, with prefixes. Prefixes tell you how many.Prefixes tell you how many.

– 1-101-10– mono, di, tri, tetra, penta, hexa, septa, mono, di, tri, tetra, penta, hexa, septa,

nona, decanona, deca» Drop a if next letter is a vowel (ex. Pentoxide)Drop a if next letter is a vowel (ex. Pentoxide)

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 appropriate ending with appropriate prefix.prefix.

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 table, name of metal ion, Get charges from table, name of metal ion,

or memorized from the list.or memorized from the list. Use parenthesis to indicate multiple Use parenthesis to indicate multiple

polyatomics.polyatomics. Use criss-cross methodUse criss-cross method

– Reduce if necessaryReduce if necessary

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

formulaformula

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

– 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 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

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.