Chapter 4Chapter 4Atoms and Atoms and ElementsElements

HomeworkHomework

Assigned Problems (Assigned Problems (oddodd numbers only) numbers only)““Questions and Problems” 4.1 to 4.65 Questions and Problems” 4.1 to 4.65

(begins on page 96)(begins on page 96)““Additional Questions and Problems” Additional Questions and Problems”

4.75 to 4.105 (page 122-123)4.75 to 4.105 (page 122-123)““Challenge Questions” 4.107 to 4.111, Challenge Questions” 4.107 to 4.111,

(page 124)(page 124)

ElementsElementsMatter is anything with a mass and occupies spaceMatter is anything with a mass and occupies spaceMatter (in our world) is composed of combinations Matter (in our world) is composed of combinations

of about 100 basic substances calledof about 100 basic substances called elements elements109 elements have been discovered and isolated 109 elements have been discovered and isolated

88 are found in nature 88 are found in nature 21 are (synthetic) man-made21 are (synthetic) man-made

Oxygen most abundant element (by mass) on earthOxygen most abundant element (by mass) on earth

““Element”Element” A pure substance that cannot be broken down into A pure substance that cannot be broken down into

simpler substances by a chemical meanssimpler substances by a chemical meansSingle atom of that elementSingle atom of that elementSample of the element large enough to weigh on a Sample of the element large enough to weigh on a

scalescaleGenerally referring to the presence of that element Generally referring to the presence of that element

(compound), not necessarily in its free form(compound), not necessarily in its free form

Chemical symbolsChemical symbolsEach element has a unique symbolEach element has a unique symbolOne or two letter abbreviationsOne or two letter abbreviations

If two letters, the second is If two letters, the second is lower caselower caseThe letter symbol often corresponds to The letter symbol often corresponds to

the name of the elementthe name of the elementF = FluorineF = FluorineP = PhosphorousP = Phosphorous

Some symbols derived from the Latin or Some symbols derived from the Latin or Greek namesGreek namesLead – Lead – PbPb (plumbum) (plumbum)Gold – Gold – AuAu (aurum) (aurum)Sodium – Sodium – NaNa (natrium) (natrium)

Names of Symbols and Some Common Names of Symbols and Some Common ElementsElements

Required: Know the name and Required: Know the name and symbol of some of the most symbol of some of the most common elementscommon elements

Table 4.2 on p. 95 (know the Table 4.2 on p. 95 (know the names and symbols listed)names and symbols listed)

A periodic table will be given on A periodic table will be given on each test or quizeach test or quiz

Required: Know how to use a Required: Know how to use a periodic table to find needed periodic table to find needed informationinformation

Periodic TablePeriodic TableA chart of the elements with similar A chart of the elements with similar

chemical properties arranged into vertical chemical properties arranged into vertical columns (columns (groupsgroups) )

Horizontal rows are called Horizontal rows are called periodsperiodsThe elements arranged (in rows) in order The elements arranged (in rows) in order

of increasing atomic mass (atomic of increasing atomic mass (atomic number)number)

Main group elements are those in the Main group elements are those in the columns labeled with numbers (1A-8A)columns labeled with numbers (1A-8A)

Transition elements are those in the Transition elements are those in the columns labeled with the letter “B” columns labeled with the letter “B”

Main Group ElementsMain Group Elements

Also calledAlso called representative elementsrepresentative elementsThe elements in the A-groupsThe elements in the A-groups

First two columns (1A and 2A)First two columns (1A and 2A)The last 6 columns (3A to 8A)The last 6 columns (3A to 8A)

Easy to predict ionic structureEasy to predict ionic structure

Transition ElementsTransition Elements

The elements in the B-groups The elements in the B-groups Middle block of elements (3B Middle block of elements (3B

through 2B)through 2B)Includes the two groups at the Includes the two groups at the

bottombottomLanthanidesLanthanides and and ActinidesActinides

Difficult to predict ionic Difficult to predict ionic structurestructure

Classification of ElementsClassification of Elements Certain groups of elements have their own Certain groups of elements have their own

special names due to the chemical similarity of special names due to the chemical similarity of the elements in themthe elements in them

Alkali MetalsAlkali MetalsGroup 1AGroup 1A

Alkaline Earth MetalsAlkaline Earth MetalsGroup 2AGroup 2A

HalogensHalogensGroup 7AGroup 7A

Noble GasesNoble GasesGroup 8AGroup 8A

Become familiar with these group namesBecome familiar with these group names

The Periodic TableThe Periodic Table1A

2A 3A 4A 5A 6A7A

8A

1

2

3

4

5

6

7

Metals/NonmetalsMetals/NonmetalsMetalsMetals

Everything to the left of the Everything to the left of the metal/nonmetal barriermetal/nonmetal barrier

Shiny solid, good conductor of Shiny solid, good conductor of electricity, ductile and malleableelectricity, ductile and malleable

NonmetalsNonmetalsEverything to the right of the Everything to the right of the

metal/nonmetal barriermetal/nonmetal barrierDull appearance, not ductile or Dull appearance, not ductile or

malleable not good conductors of malleable not good conductors of electricityelectricity

MetalloidsMetalloidsElements with properties Elements with properties

intermediate between those intermediate between those metals and nonmetalsmetals and nonmetals

On the metal/nonmetal barrierOn the metal/nonmetal barrierHave some physical properties Have some physical properties

of metals but some chemical of metals but some chemical properties of nonmetalsproperties of nonmetals

SemiconductorsSemiconductors SiSi, , GeGe, As, , As, SbSb, Te, Te

The AtomThe AtomThe smallest particle of an The smallest particle of an

element that can exist and still element that can exist and still have properties of that elementhave properties of that element

All atoms of a certain type are All atoms of a certain type are similarsimilar to one another and to one another and different from all other typesdifferent from all other types

109 different types are known 109 different types are known and each “type” is a different and each “type” is a different elementelement

Dalton’s Atomic Theory (1808)Dalton’s Atomic Theory (1808) A set of five statements that A set of five statements that

summarize the modern summarize the modern scientific concept about atomsscientific concept about atoms

1)1) All matter is made from small All matter is made from small particles called atoms (109 particles called atoms (109 different types)different types)

2)2) All atoms of a given type are All atoms of a given type are similar to one another and similar to one another and significantly different from all significantly different from all other typesother types

`

Dalton’s Atomic TheoryDalton’s Atomic Theory3)3) The number and arrangement of The number and arrangement of

different types of atoms in a pure different types of atoms in a pure substance determine its identitysubstance determine its identity

4)4) A chemical change is a A chemical change is a combination, separation, or combination, separation, or rearrangement of atoms (forms rearrangement of atoms (forms new substances)new substances)

5)5) Only whole atoms take part or Only whole atoms take part or result from any chemical reactionresult from any chemical reaction

`

Dalton’s Atomic TheoryDalton’s Atomic TheoryAtoms are Atoms are indivisibleindivisible in a chemical in a chemical

process (indestructible)process (indestructible)All atoms present at beginning are All atoms present at beginning are

present at the endpresent at the endAtoms are not created or Atoms are not created or

destroyed, just rearrangeddestroyed, just rearrangedAtoms of one element cannot Atoms of one element cannot

change into atoms of another change into atoms of another elementelementCannot turn Lead into Gold by a Cannot turn Lead into Gold by a chemical reactionchemical reaction

Cathode Rays and ElectronsCathode Rays and Electrons J.J. Thomson (1897) used a gas discharge tube to investigate a J.J. Thomson (1897) used a gas discharge tube to investigate a

beam called a beam called a cathode raycathode ray Determined that the ray was made of tiny negatively charged Determined that the ray was made of tiny negatively charged

particles we call particles we call electronselectrons He determined the electrons were smaller than a hydrogen He determined the electrons were smaller than a hydrogen

atom atom Since electrons are smaller than atoms they must be parts of Since electrons are smaller than atoms they must be parts of

an atoman atom Atoms must be divisibleAtoms must be divisible Atoms of different elements all produced these same electronsAtoms of different elements all produced these same electrons

Parts of an Atom: The ElectronParts of an Atom: The Electron

Defined by ThompsonDefined by ThompsonTiny, negatively charged Tiny, negatively charged

particleparticleCharge is -1Charge is -1

Very light compared to mass of Very light compared to mass of atomatom1/20001/2000thth the mass of a H atom the mass of a H atom

Moves very rapidly within the Moves very rapidly within the atomatom

Thompson’s Model of AtomsThompson’s Model of AtomsAtoms have a structure and are Atoms have a structure and are divisibledivisibleThomson reasoned that electrons must Thomson reasoned that electrons must

be a fraction of the entire size of the be a fraction of the entire size of the atom since their mass is much smaller atom since their mass is much smaller that the whole atomthat the whole atom

Thomson also reasoned since atoms are Thomson also reasoned since atoms are neutral, the electrons were embedded in neutral, the electrons were embedded in a sphere of uniform positive charge a sphere of uniform positive charge

Thomson (1898) proposed the “Thomson (1898) proposed the “Plum Plum PuddingPudding” model or “” model or “Raisin MuffinRaisin Muffin” model ” model of the atomof the atom

Thompson’s Model of AtomsThompson’s Model of Atoms Thomson Atomic Thomson Atomic

Model (early 1900’s):Model (early 1900’s): Proposed a uniform, Proposed a uniform, positive sphere of positive sphere of matter with small matter with small negative electrons negative electrons attached to the attached to the surface of the spheresurface of the sphere

This became known This became known as the as the plum-pudding plum-pudding modelmodel

Rutherford’s ExperimentRutherford’s Experiment

1911 1911 RutherfordRutherford designed an experiment designed an experiment to test the to test the Thompson modelThompson model (“ (“plum-plum-puddingpudding”) of the atom ”) of the atom

Rutherford directed positively charged Rutherford directed positively charged particles (alpha particles) towards a thin particles (alpha particles) towards a thin gold foil sheetgold foil sheet

Rutherford expected the particles to pass Rutherford expected the particles to pass straight through a uniform area of mass straight through a uniform area of mass and positive chargeand positive charge

Fig4_5

Beam of particles

Thinmetal foilScreen to detect

scattered particles

Some particles are scattered

Source of particles

Most particlespass straightthrough foil

Rutherford’s ExperimentRutherford’s Experiment

Rutherford’s ExperimentRutherford’s ExperimentResults:Results:Most (alpha) particles Most (alpha) particles

mostly went straight mostly went straight throughthrough

A few particles were A few particles were unexpectedly deflected unexpectedly deflected from their expected from their expected (straight) path(straight) path

A few deflected nearly A few deflected nearly back towards alpha back towards alpha particle sourceparticle source

Rutherford’s ExperimentRutherford’s Experiment

Rutherford proposed:Rutherford proposed:A very small, dense core at the center of A very small, dense core at the center of

the atomthe atomThis dense core was called the “This dense core was called the “nucleusnucleus””It contains most of the mass of the atom It contains most of the mass of the atom

and it has a positive charge (and it has a positive charge (protonsprotons) ) Most of an atom is empty space filled with Most of an atom is empty space filled with

electronselectrons

Parts of an AtomParts of an Atom

Experimentation in the early 20Experimentation in the early 20 thth century ( century (ThomsonThomson and and RutherfordRutherford) proved atoms were ) proved atoms were notnot indivisibleindivisible spheresspheres

Atoms are comprised of smaller particles: Atoms are comprised of smaller particles: Subatomic particlesSubatomic particles

More experiments led to the discovery of two more More experiments led to the discovery of two more fundamental subatomic particles: Protons and fundamental subatomic particles: Protons and neutronsneutrons Electron: Negatively charged (1897)Electron: Negatively charged (1897) Proton: Positively charged (1919)Proton: Positively charged (1919) Neutron: No electrical charge (1932)Neutron: No electrical charge (1932)

Nucleus of the Atom (Rutherford Model)Nucleus of the Atom (Rutherford Model)

A very dense, small center exists in the A very dense, small center exists in the center of the atom called the center of the atom called the nucleusnucleus Volume of nucleus is about 1/10 trillionth the volume of Volume of nucleus is about 1/10 trillionth the volume of

the entire atomthe entire atom

Nucleus is basically the entire mass of the Nucleus is basically the entire mass of the atomatom The The protonsprotons and and neutronsneutrons are located in the nucleus are located in the nucleus Most of the atom is empty space with fast-moving Most of the atom is empty space with fast-moving

electronselectrons

Nucleus of the Atom (Rutherford Model)Nucleus of the Atom (Rutherford Model) The The nucleusnucleus is the is the

center (core) of the center (core) of the atomatom

The nucleus The nucleus has most of the has most of the mass of the atommass of the atomprotonsprotonsneutronsneutrons

The The extranuclear extranuclear regionregion it contains all the it contains all the

electronselectrons

nucleusnucleusExtranuclear Extranuclear regionregion

Nucleus of the Atom (Rutherford Model)Nucleus of the Atom (Rutherford Model)

The nucleus is the core of the atomThe nucleus is the core of the atomPositively chargedPositively chargedContains most of the mass of the Contains most of the mass of the

atomatomWithin a neutral atom, there are Within a neutral atom, there are

equal numbers of protons and equal numbers of protons and electrons, so atom has a net electrons, so atom has a net charge of zerocharge of zero

Mass of Subatomic Particles:Mass of Subatomic Particles:The ProtonThe Proton

The proton:The proton:Has the same magnitude charge as the electron, Has the same magnitude charge as the electron,

but oppositely chargedbut oppositely chargedHas a charge of +1Has a charge of +1Weighs about 2000 times an electronWeighs about 2000 times an electronIs found in the nucleusIs found in the nucleus

In a neutral atom: In a neutral atom:

Number of protons = identity of the compoundNumber of protons = identity of the compound

Number of protons = number of electronsNumber of protons = number of electrons

Mass of Subatomic Particles:Mass of Subatomic Particles:The NeutronThe Neutron

The last of the three subatomic The last of the three subatomic particles to be discovered, also particles to be discovered, also located in the nucleuslocated in the nucleus

The mass is about the same as a The mass is about the same as a protonproton

Has no charge (neutral)Has no charge (neutral)Variable amounts are possible in Variable amounts are possible in

atoms of the same elementatoms of the same elementThis is the basis for This is the basis for isotopesisotopes

Mass of Subatomic ParticlesMass of Subatomic Particles

The three subatomic particles have The three subatomic particles have extremely small massesextremely small masses

Chemists base the mass of atoms on the Chemists base the mass of atoms on the atomic mass scaleatomic mass scale

A relative scale based on the mass of A relative scale based on the mass of one carbon atom: one carbon atom: 12.00 amu12.00 amu

One amu is 1/12 the mass of one carbon One amu is 1/12 the mass of one carbon atom, so the approximate mass of one atom, so the approximate mass of one proton or neutron is proton or neutron is 1.00 amu1.00 amu

Atomic Number (Z) Atomic Number (Z) All elements in periodic table arranged All elements in periodic table arranged

according to the atomic numberaccording to the atomic numberEqual to the number of protons in the Equal to the number of protons in the

nucleus of an atomnucleus of an atom

Determines the Determines the identityidentity of the atom of the atomIs also equal to the Is also equal to the number of electronsnumber of electrons in in

the neutral atomthe neutral atomThe top number in each square in the The top number in each square in the

periodic tableperiodic table

Atomic Number = number of protons in an atomAtomic Number = number of protons in an atom

Mass Number (A)Mass Number (A)The total number of protons and neutrons in The total number of protons and neutrons in

an atoman atom

Mass number is always a Mass number is always a whole number whole number ((no decimalsno decimals))

An oxygen atom has a mass number of 16 An oxygen atom has a mass number of 16 ((8 protons and 8 neutrons8 protons and 8 neutrons))

Mass Number = number of protons + number of neutronsMass Number = number of protons + number of neutrons

Isotopes and Atomic MassIsotopes and Atomic Mass All atoms of the All atoms of the samesame elementelement have the same have the same

atomic numberatomic number ( (ZZ) ) The same element can differ in the The same element can differ in the mass numbermass number

((AA) due to a different number of neutrons) due to a different number of neutrons All Mg atoms have 12 protons, but may have 12, 13, All Mg atoms have 12 protons, but may have 12, 13,

or 14 neutronsor 14 neutrons

Isotopes and Atomic MassIsotopes and Atomic MassAtoms that have the same number of Atoms that have the same number of

protons and electrons but different protons and electrons but different numbers of neutrons are called numbers of neutrons are called isotopesisotopes

Since isotopes are atoms of the same Since isotopes are atoms of the same element,element, They have the same atomic numberThey have the same atomic numberThey display the same chemical They display the same chemical

propertiesproperties

Nuclear (Isotopic) SymbolsNuclear (Isotopic) SymbolsA notation used when necessary to A notation used when necessary to

differentiate between isotopesdifferentiate between isotopes

ZA X

A is the mass numberZ is the atomic numberX is the chemical symbol

Atomic MassAtomic Mass

A specific element can have several A specific element can have several mass values if it exists in isotopic formsmass values if it exists in isotopic forms

For example, oxygen atoms can have For example, oxygen atoms can have any one of three masses but often any one of three masses but often treated as if it has one masstreated as if it has one mass

The The atomic massatomic mass of an element is the of an element is the mass of the “average atom” of that mass of the “average atom” of that elementelement

Atomic MassAtomic Mass

Atomic mass is a Atomic mass is a ““weighted average weighted average massmass” based on:” based on:

1)1) The number of The number of isotopes that exist isotopes that exist for the elementfor the element

2)2) The relative mass of The relative mass of each isotopeeach isotope

3)3) The percent The percent abundance of each abundance of each isotopeisotope

Example:Example:Isotopes and Atomic MassIsotopes and Atomic Mass

Complete the following table:Complete the following table:Symbol Name # Protons #Neutrons #Electrons

11H

919 F

2964 Cu

12 H

Hydrogen

Fluorine

Copper

Hydrogen

1

9

29

1

0

10

35

1

1

9

29

1

endendRemaining slides (Section 4.6) Remaining slides (Section 4.6)

will continue with chapter 10will continue with chapter 10

Electron Energy LevelsElectron Energy Levels Electrons possess energy; they are in constant motion in the large Electrons possess energy; they are in constant motion in the large

empty space of the atomempty space of the atom The arrangement of electrons in an atom corresponds to an The arrangement of electrons in an atom corresponds to an

electron’s energyelectron’s energy The electron resides outside the nucleus in one of seven fixed The electron resides outside the nucleus in one of seven fixed

energy levelsenergy levels Energy levels are Energy levels are quantized: quantized: Only certain energy values are allowedOnly certain energy values are allowed

Electron Energy LevelsElectron Energy LevelsElectrons of similar energy are grouped Electrons of similar energy are grouped

into energy levelsinto energy levelsThe major energy levels in an atom are The major energy levels in an atom are

called the principal shells symbolized called the principal shells symbolized by by n,n, the principal quantum number the principal quantum number

As As nn goes from 1 to 2, 3, 4, etc., the goes from 1 to 2, 3, 4, etc., the electron’s energy and distance from the electron’s energy and distance from the nucleus increasesnucleus increases

The maximum number of electrons in The maximum number of electrons in an energy level is equal to an energy level is equal to 22nn22

Electron ArrangementsElectron ArrangementsThe chemical properties of an element are The chemical properties of an element are

determined by the number and arrangement determined by the number and arrangement of electrons in the nucleusof electrons in the nucleus

The electron arrangement (configuration) is The electron arrangement (configuration) is a statement of the number of electrons in a statement of the number of electrons in each energy leveleach energy level

The number of electrons an atom has of The number of electrons an atom has of various energiesvarious energies

The electron arrangements of the first 18 The electron arrangements of the first 18 elements can be written by placing electrons elements can be written by placing electrons in order of increasing energy in order of increasing energy

Valence ElectronsValence ElectronsThe electrons that reside in the The electrons that reside in the

highest energy level (highest energy level (nn))They are the furthest electrons They are the furthest electrons

from the nucleusfrom the nucleusDetermine the chemical properties Determine the chemical properties

of an elementof an elementNumber at the top of each column Number at the top of each column

for elements (for elements (1A-8A1A-8A) equals the ) equals the number of valence electrons for number of valence electrons for each element in that groupeach element in that group

Electron-Dot SymbolsElectron-Dot SymbolsConsists of an element’s symbol and one Consists of an element’s symbol and one

dot for each valence electron placed about dot for each valence electron placed about the symbolthe symbol

Used only for main group elements Used only for main group elements (1A to 8A)(1A to 8A)

Main group elements in the same group Main group elements in the same group have the same number of valence have the same number of valence electronselectrons

The number of valence electrons is the The number of valence electrons is the same as the group numbersame as the group number

Electron-Dot SymbolsElectron-Dot Symbols

Electron-Dot SymbolsElectron-Dot SymbolsWrite the symbol of the elementWrite the symbol of the elementDetermine the number of valence Determine the number of valence

electrons by the group numberelectrons by the group numberUse dot or X to represent an electronUse dot or X to represent an electron

Li• Be• •B• •C• •N• •O: :F: :Ne:• •

•

• • • •

•• •• •• ••

••

Li• Li+1 :F: [:F:]-1

•

•• ••

••

Group Number1 2 3 4 5 6 7 8

Determine the number of valence Determine the number of valence electrons for Ba, As, and Br. electrons for Ba, As, and Br.

Write the electron-dot symbol for each Write the electron-dot symbol for each of these elementsof these elementsBa: 2 valence electronsBa: 2 valence electrons

As: 5 valence electronsAs: 5 valence electrons

Br: 7 valence electronsBr: 7 valence electrons

Electron-dot symbols Electron-dot symbols ExamplesExamples

Ba

Br

As

Ionization EnergyIonization EnergyEnergy needed to remove one electron from Energy needed to remove one electron from

an atom in the gas statean atom in the gas state It measures how tightly an atom holds its It measures how tightly an atom holds its

electrons electrons The lower the ionization energy, the easier it The lower the ionization energy, the easier it

is to remove the electronis to remove the electronMetals have low ionization energiesMetals have low ionization energiesNonmetals have high ionization energies Nonmetals have high ionization energies

Ionization Energy Ionization Energy decreasesdecreases down the group down the group Ionization Energy Ionization Energy increasesincreases across the across the

periodperiodLeft to rightLeft to right

Ionization EnergyIonization EnergyThe more tightly an electron is held, The more tightly an electron is held,

the higher the ionization energythe higher the ionization energyThe outermost electrons are the The outermost electrons are the

easiest to remove; as the energy level easiest to remove; as the energy level increasesincreases the the fartherfarther the electron is the electron is from the nucleusfrom the nucleus

As As nn gets larger, removal of an electron gets larger, removal of an electron requires less energyrequires less energy

Helium requires the most energy of any Helium requires the most energy of any element due to its full (stable) energy element due to its full (stable) energy level level

endend