Elements and Atoms Chapter Two. Wolpa/Advanced Placement Chemistry Introduction This chapter describes the origins of atomic theory, the discovery and

Elements and AtomsElements and Atoms

Chapter TwoChapter Two

Wolpa/Advanced Placement ChemWolpa/Advanced Placement Chemistryistry

IntroductionIntroduction

This chapter describes the origins of atomic This chapter describes the origins of atomic theory, the discovery and characterization of theory, the discovery and characterization of subatomic particles and the locations of these subatomic particles and the locations of these particles in atoms, as well as the method of particles in atoms, as well as the method of designating the composition of individual atoms. designating the composition of individual atoms. The existence of isotopes of elements are also The existence of isotopes of elements are also discussed. The arrangement of the elements in discussed. The arrangement of the elements in the periodic table is then described followed by the periodic table is then described followed by the introduction of the mole as the quantity of the introduction of the mole as the quantity of matter that connects the submicroscopic world of matter that connects the submicroscopic world of atoms with the macroscopic world in which we atoms with the macroscopic world in which we live.live.


Origins of the Atomic TheoryOrigins of the Atomic Theory

• Ancient GreeksAncient Greeks

The simple picture of atoms as tiny spheres in The simple picture of atoms as tiny spheres in constant motion goes back a long way in history constant motion goes back a long way in history - to the Greek philosopher Leucippus and his - to the Greek philosopher Leucippus and his student, Democritus (460 - 370 BC). Democritus student, Democritus (460 - 370 BC). Democritus reasoned that if a bit of matter were divided into reasoned that if a bit of matter were divided into smaller and smaller pieces, one would ultimately smaller and smaller pieces, one would ultimately arrive at a tiny particle that could not be further arrive at a tiny particle that could not be further divided. He described this particle with the word divided. He described this particle with the word "atom" which means uncuttable. This theory "atom" which means uncuttable. This theory was, however, untestable and unsupported and was, however, untestable and unsupported and remained so for more than 2000 years.remained so for more than 2000 years.


LavoisierLavoisier

Antoine LavoisierAntoine Lavoisier (1743-1794) - (1743-1794) - showed that when a compound is showed that when a compound is combusted (reacted with oxygen) in a combusted (reacted with oxygen) in a closed system, there is no loss in mass. closed system, there is no loss in mass. This lead to the This lead to the Law of Conservation Law of Conservation of Massof Mass, which states "mass can , which states "mass can neither be created or destroyed in neither be created or destroyed in chemical reactions."chemical reactions."


ProustProust

Joseph ProustJoseph Proust (1754-1826) - (1754-1826) - formulated the Law of Definite formulated the Law of Definite Proportions, which states "different Proportions, which states "different samples of a pure chemical substance samples of a pure chemical substance contain the same proportion of elements contain the same proportion of elements by mass.“by mass.“

Also called the Law of Constant Also called the Law of Constant Composition -Composition -


John Dalton and his Atomic John Dalton and his Atomic TheoryTheory

John DaltonJohn Dalton (1766-1826) combined (1766-1826) combined the Law of Definite Proportions and the Law of Definite Proportions and the Law of Conservation of Mass and the Law of Conservation of Mass and formulated an Atomic Theory.formulated an Atomic Theory.

1803 - Dalton linked the existence of 1803 - Dalton linked the existence of elements, which cannot be elements, which cannot be decomposed chemically, to the idea decomposed chemically, to the idea of atoms, which are indivisible.of atoms, which are indivisible.


PostulatesPostulates

All matter is made of atoms. These All matter is made of atoms. These indivisible and indestructible objects indivisible and indestructible objects are the ultimate chemical particles.are the ultimate chemical particles.

All atoms of a given element are All atoms of a given element are identical, both in mass and in identical, both in mass and in properties. Atoms of different properties. Atoms of different elements have different masses and elements have different masses and different properties.different properties.


Postulates cont.Postulates cont.

Compounds are formed by combination of Compounds are formed by combination of two or more different kinds of atoms. Atoms two or more different kinds of atoms. Atoms combine in the ratio of small whole numbers, combine in the ratio of small whole numbers, fro example, one atom of A with one atom of fro example, one atom of A with one atom of B, or two atoms of A with one atom of B.B, or two atoms of A with one atom of B.

Atoms are the units of chemical change. A Atoms are the units of chemical change. A chemical reaction involves only combination, chemical reaction involves only combination, separation, or rearrangement of atoms, but separation, or rearrangement of atoms, but atoms are not created, destroyed, divided atoms are not created, destroyed, divided into parts, or converted into other kinds of into parts, or converted into other kinds of atoms during a chemical reaction.atoms during a chemical reaction.


ExplainedExplained

Lavoisier's Law of Conservation of Matter - Lavoisier's Law of Conservation of Matter - Matter cannot be created or destroyed Matter cannot be created or destroyed because atoms cannot be created or because atoms cannot be created or destroyed.destroyed.

Proust's Law of Constant Composition - If all Proust's Law of Constant Composition - If all atoms of a given element are identical, and atoms of a given element are identical, and all compounds are formed by atoms in small all compounds are formed by atoms in small whole number ratios - then the mass percent whole number ratios - then the mass percent of an element in a given compound will of an element in a given compound will always be the same.always be the same.


ProposedProposed

Law of Multiple Proportions - When Law of Multiple Proportions - When two elements form two different two elements form two different compounds, the mass ratio in one compounds, the mass ratio in one compound is a small whole number compound is a small whole number times the mass ratio in the other. times the mass ratio in the other.


Law of Multiple ProportionsLaw of Multiple Proportions


Atomic StructureAtomic Structure


ElectricityElectricity

Electricity is involved in many of the experiments Electricity is involved in many of the experiments from which the theory of atomic structure was from which the theory of atomic structure was derived.derived.

Electrical charge was first observed and recorded Electrical charge was first observed and recorded by the ancient Egyptians - amber attracted small by the ancient Egyptians - amber attracted small objects when rubbed with wool or silk.objects when rubbed with wool or silk.

Benjamin Franklin - positive and negative Benjamin Franklin - positive and negative charges; conservation of chargecharges; conservation of charge

Experiments with electroscope - unlike charges Experiments with electroscope - unlike charges attract one another, like charges repel one attract one another, like charges repel one anotheranother


ResultResult

Electrical charges must be Electrical charges must be associated with matter - perhaps associated with matter - perhaps atoms!atoms!


RadioactivityRadioactivity

Henri Becquerel (1896) - Discovered that Henri Becquerel (1896) - Discovered that uranium ore emitted rays when exposed to uranium ore emitted rays when exposed to photographic platesphotographic plates

Marie Curie (1898) - Isolated polonium and Marie Curie (1898) - Isolated polonium and radium, which also emitted the same kind radium, which also emitted the same kind of rays. (1899) She suggested that atoms of rays. (1899) She suggested that atoms of radioactive substances disintegrated of radioactive substances disintegrated when they emit these rays - named the when they emit these rays - named the phenomenon radioactivity.phenomenon radioactivity.


Types of RadiationTypes of Radiation

alpha, beta, gammaalpha, beta, gamma


ResultResult

The suggestion that atoms The suggestion that atoms disintegrate contradicts Dalton's idea disintegrate contradicts Dalton's idea that atoms are indivisible, requires that atoms are indivisible, requires an extension of Dalton's theory.an extension of Dalton's theory.


ElectronsElectrons

Michael Faraday (1833) - Same Michael Faraday (1833) - Same current used in electrolysis caused current used in electrolysis caused different quantities of different different quantities of different metals to deposit. these quantities metals to deposit. these quantities were related to the relative masses were related to the relative masses of the atoms of those elements. A of the atoms of those elements. A fundamental particle of electricity fundamental particle of electricity must exist - electron.must exist - electron.


Cathode RaysCathode Rays

Travel in straight lines, cause sharp Travel in straight lines, cause sharp shadows, cause gases and shadows, cause gases and fluorescent materials to glow, can fluorescent materials to glow, can heat metal objects red hot, can be heat metal objects red hot, can be deflected by a magnetic field, and deflected by a magnetic field, and are attracted toward positively are attracted toward positively charged plates.charged plates.


J.J. ThomsonJ.J. Thomson

(1897) - Calculated the charge to (1897) - Calculated the charge to mass ratio for particles in cathode mass ratio for particles in cathode ray beam by applying magnetic and ray beam by applying magnetic and electrical fields and using basic laws electrical fields and using basic laws of electricity and magnetism.of electricity and magnetism.


J.J. Thomson’s ExperimentJ.J. Thomson’s Experiment


Robert MillikanRobert Millikan

Oil Drop Experiment - Measured Oil Drop Experiment - Measured charge on particle. (1.60 x 10charge on particle. (1.60 x 10-19-19 C) C)


RESULTRESULT

electron mass = 9.109389 x 10electron mass = 9.109389 x 10-28-28 g; g;

charge = -1.60217733 x 10charge = -1.60217733 x 10-19-19 C. C.


So! Thompson has discovered the electron, and it must live inside atoms.

It is much less massive than the the atom itself, so perhaps we have little electrons stuffed into the ‘rest’ of the atom like raisins in the oatmeal, or:

Plum Pudding...


ProtonsProtons

Canal rays - observed in a special cathode-ray Canal rays - observed in a special cathode-ray tube with perforated cathode. Ray opposite tube with perforated cathode. Ray opposite to cathode ray is observed. Charge to mass to cathode ray is observed. Charge to mass ratio for the positive particles differed. ratio for the positive particles differed. Hydrogen has largest charge to mass ratio- Hydrogen has largest charge to mass ratio- suggests hydrogen provides positive particles suggests hydrogen provides positive particles with the smallest mass - these were with the smallest mass - these were considered to be fundamental positively considered to be fundamental positively charged particles of atomic structure and charged particles of atomic structure and were later called protons by E. Rutherford.were later called protons by E. Rutherford.


ResultResult

proton mass = 1.672623 x 10proton mass = 1.672623 x 10-24-24 g; g; charge is equal and opposite to charge is equal and opposite to electron.electron.


NeutronsNeutrons

Chadwick (1932) discovers neutronChadwick (1932) discovers neutron RESULT - neutron mass = 1.6749286 RESULT - neutron mass = 1.6749286

x 10-24 g; charge = 0x 10-24 g; charge = 0


NucleusNucleus

J.J. Thomson - proposed that the atom was J.J. Thomson - proposed that the atom was a uniform sphere of positively charged a uniform sphere of positively charged matter within which thousands of electrons matter within which thousands of electrons circulated in coplanar rings. Tested theory circulated in coplanar rings. Tested theory by directing a beam of electrons at a very by directing a beam of electrons at a very thin metal foil - expected results - many thin metal foil - expected results - many deflections - did not occur.deflections - did not occur.

Ernest Rutherford (1910)- tested Ernest Rutherford (1910)- tested Thomson’s model by directing a beam of Thomson’s model by directing a beam of alpha particles at thin foil of metal.alpha particles at thin foil of metal.


Rutherford’s ExperimentRutherford’s Experiment


Rutherford’s ExperimentRutherford’s Experiment


Top:Top: Expected results: alpha particles passing through the Expected results: alpha particles passing through the plum plum

pudding model of the atom undisturbed.pudding model of the atom undisturbed.

Bottom:Bottom: Observed results: a small portion of the particles were Observed results: a small portion of the particles were

deflected, indicating a small, concentrated positive charge.deflected, indicating a small, concentrated positive charge.

http://en.wikipedia.org/wiki/Image:Rutherford_gold_foil_experiment_results.svg


ResultsResults

All of the positive charge and most of All of the positive charge and most of the mass of the atom is concentrated the mass of the atom is concentrated in a very small volume - the nucleus. in a very small volume - the nucleus. The electrons occupy the rest of the The electrons occupy the rest of the space in the atom.space in the atom.


Important NotesImportant Notes

To chemists the electrons are the To chemists the electrons are the most important part of the atom, most important part of the atom, because they are the first part of the because they are the first part of the atom that contacts another atom. atom that contacts another atom.

Number of protons and electrons are Number of protons and electrons are equal in a given atomequal in a given atom


Atomic CompositionAtomic Composition

electron electron mass = 9.109389 x 10mass = 9.109389 x 10-28-28 g; g;charge = -1.60217733 x charge = -1.60217733 x

1010-19-19 C C

proton proton mass = 1.672623 x 10mass = 1.672623 x 10-24-24 g; g; charge is equal and opposite charge is equal and opposite

to to electron.electron.

neutron neutron mass = 1.6749286 x 10mass = 1.6749286 x 10-24-24 g; g; charge = 0charge = 0


NucleusNucleus

Nucleus is made up of protons and Nucleus is made up of protons and neutrons; electrons are found in neutrons; electrons are found in space about the nucleus. space about the nucleus.


Electrically Neutral AtomsElectrically Neutral Atoms

For an atom which has no net For an atom which has no net electrical charge, the number of electrical charge, the number of negatively charged electrons around negatively charged electrons around the nucleus equals the number of the nucleus equals the number of positively charged protons in the positively charged protons in the nucleusnucleus


Atomic NumberAtomic Number

All atoms of the same element have All atoms of the same element have the same number of protons in the the same number of protons in the nucleus. this number is called the nucleus. this number is called the atomic number and is given the atomic number and is given the symbol Z.symbol Z.


Mass NumberMass Number

The sum of the number of protons The sum of the number of protons and neutrons in an atom is called the and neutrons in an atom is called the mass number and is represented mass number and is represented with the symbol A.with the symbol A.


Nuclear Symbol of an AtomNuclear Symbol of an Atom


IsotopesIsotopes

Atoms having the same atomic Atoms having the same atomic number Z but a different mass number Z but a different mass number A. Isotopes are atoms of the number A. Isotopes are atoms of the same element, but they have same element, but they have different masses because they have different masses because they have different numbers of neutrons.different numbers of neutrons.


Atomic MassAtomic Mass

The atomic mass of a given atom is based The atomic mass of a given atom is based on a scale that is relative to a standard. on a scale that is relative to a standard. That standard is the mass of a carbon atom That standard is the mass of a carbon atom that has six protons and six neutrons in its that has six protons and six neutrons in its nucleus. Such an atom is defined to have a nucleus. Such an atom is defined to have a mass of exactly 12 atomic mass units. The mass of exactly 12 atomic mass units. The actual masses of atoms have been actual masses of atoms have been determine experimentally using mass determine experimentally using mass spectrometers.spectrometers.


Calculation of Atomic MassCalculation of Atomic Mass

The atomic mass given for an element on The atomic mass given for an element on the periodic table is a weighed average the periodic table is a weighed average determined from the masses and determined from the masses and abundances of the various isotopes of a abundances of the various isotopes of a given element.given element.

atomic mass = atomic mass = (%isotope 1/100) (mass of isotope 1) + (%isotope 1/100) (mass of isotope 1) +

(%isotope 2/100) (mass of isotope 2) + etc (%isotope 2/100) (mass of isotope 2) + etc


Calculating atomic massesCalculating atomic masses

for boron, 19.9% occurs as for boron, 19.9% occurs as 1010B and B and 80.1% occurs as 80.1% occurs as 1111B. The isotopic B. The isotopic mass of mass of 1010B is 10.013 and B is 10.013 and 1111B is B is 11.00911.009 1010B 0.199 B 0.199 10.013 amu = 1.99 amu 10.013 amu = 1.99 amu 1111B 0.801 B 0.801 11.009 amu = 8.82 amu 11.009 amu = 8.82 amu Atomic mass of boron = 10.81 amuAtomic mass of boron = 10.81 amu



Atomic Mass and Periodic Atomic Mass and Periodic TableTable

An element is a group of atoms all An element is a group of atoms all having the same atomic number having the same atomic number although the mass number may differ. although the mass number may differ. The mass of the atoms is a relative The mass of the atoms is a relative mass based on using carbon -12 as the mass based on using carbon -12 as the standard reference. The mass reported standard reference. The mass reported on the periodic table is a weighted on the periodic table is a weighted average based on the percentages of average based on the percentages of all the naturally occurring isotopes.all the naturally occurring isotopes.


Relative MassRelative Mass

Each element has an average Each element has an average relative mass based on C-12. It relative mass based on C-12. It follows logically that if you mass out follows logically that if you mass out the gram relative mass there must the gram relative mass there must be the same number of atoms for all be the same number of atoms for all the elements.the elements.


ElementElement Relative Mass of Relative Mass of Number of atoms in Number of atoms in

the the one atom in "u"one atom in "u" gram relative massgram relative mass

HH 1.00791.0079 NN OO 15.999415.9994 NN NaNa 22.9897722.98977 NN


One of the ways would be like this: take the actual One of the ways would be like this: take the actual mass of the element and see how many atoms it mass of the element and see how many atoms it would take to get the relative mass in grams.would take to get the relative mass in grams.

electron mass = 9.1093897 x 10electron mass = 9.1093897 x 10-28-28

proton mass = 1.6726231 x 10proton mass = 1.6726231 x 10-24-24

neutron mass = 1.6749286 x 10neutron mass = 1.6749286 x 10-24-24

The average value - when this is done over and The average value - when this is done over and over - and when the mass defect of the nucleus is over - and when the mass defect of the nucleus is taken into account is called Avogadro's number taken into account is called Avogadro's number and it is equal to 6.022 x 10and it is equal to 6.022 x 102323. We call this a mole.. We call this a mole.


The Mole - DefinitionThe Mole - Definition

A mole is the amount of substance A mole is the amount of substance that contains as many elementary that contains as many elementary entities (atoms, molecules, or other entities (atoms, molecules, or other particles) as there are atoms in particles) as there are atoms in exactly 12 g of the carbon - 12 exactly 12 g of the carbon - 12 isotope.isotope.


The Mole – cont.The Mole – cont.

One mole of an element impliesOne mole of an element implies The atomic mass expressed in grams, The atomic mass expressed in grams,

different for each elementdifferent for each element Avogadro’s number of atoms, which is Avogadro’s number of atoms, which is

the the samesame for all elements for all elements A conversion factor between mass and A conversion factor between mass and

numbers of things (allows us to count numbers of things (allows us to count atoms by weighing)atoms by weighing)


Molar MassMolar Mass

When dealing with the elements in the When dealing with the elements in the laboratory we work with gram masses laboratory we work with gram masses and when we use the same gram mass and when we use the same gram mass as the relative atomic mass we call it a as the relative atomic mass we call it a molar mass - it represents the mass in molar mass - it represents the mass in grams of one mole of the element. grams of one mole of the element.


Mole of JuJuBesMole of JuJuBes

The area of the 48 contiguous United The area of the 48 contiguous United States is 3.02 x 10States is 3.02 x 1066 square miles. If square miles. If you have a mole of JuJuBes and you you have a mole of JuJuBes and you covered the United States, how thick covered the United States, how thick of a layer would you have?of a layer would you have?



ExamplesExamples

One mole of hydrogen atoms One mole of hydrogen atoms contains Avogadro's number of contains Avogadro's number of hydrogen atoms and has a mass of hydrogen atoms and has a mass of 1.0079 grams. We usually write this 1.0079 grams. We usually write this as 1.0079 grams/moleas 1.0079 grams/mole


One mole of water molecules One mole of water molecules contains Avogadro's number of water contains Avogadro's number of water molecules and has a mass of molecules and has a mass of 2(1.0079) + 15.9994 = 18.0152 2(1.0079) + 15.9994 = 18.0152 grams. Again - 18.0152 grams/mole.grams. Again - 18.0152 grams/mole.


One mole of sodium chloride formula One mole of sodium chloride formula units contains Avogadro's number of units contains Avogadro's number of formula units and has a mass of formula units and has a mass of 22.98977 + 35.453 = 58.443 grams - 22.98977 + 35.453 = 58.443 grams - 58.443 grams/mole.58.443 grams/mole.


ConversionsConversions



Elemental DistributionElemental Distribution

The Earth has 88 elements present in The Earth has 88 elements present in measurable amounts, but 10 measurable amounts, but 10 constitute <99% of the crustconstitute <99% of the crust

There are 114 know elements (26 There are 114 know elements (26 spontaneously decay into other spontaneously decay into other elements)elements)

The human body is 93% carbon, The human body is 93% carbon, hydrogen and oxygenhydrogen and oxygen


Names and Symbols of the Names and Symbols of the ElementsElements

Symbol - usually the first or second letters Symbol - usually the first or second letters of the nameof the name for two letter symbols, the first letter is for two letter symbols, the first letter is

capitalized but the second is notcapitalized but the second is not two letters are used for most elementstwo letters are used for most elements

When the name and symbol use different When the name and symbol use different letters, that means the element was known letters, that means the element was known in antiquity, and the Latin name was used in antiquity, and the Latin name was used for the basis of the symbol. The only for the basis of the symbol. The only exception is Tungsten, which uses the exception is Tungsten, which uses the German name (Wolfram)German name (Wolfram)


Grouping the elementsGrouping the elements

The elements are grouped in several The elements are grouped in several categories, according to properties categories, according to properties and therefore according to position in and therefore according to position in the periodic table.the periodic table.

Two major groupings are metals and Two major groupings are metals and nonmetalsnonmetals


The Periodic TableThe Periodic Table

Elements were originally arranged in Elements were originally arranged in columns by chemical properties, then columns by chemical properties, then atomic weight (Mendeleev)atomic weight (Mendeleev)

The modern periodic table has the The modern periodic table has the elements by atomic number (Moseley)elements by atomic number (Moseley)

The periodic law - the properties of the The periodic law - the properties of the elements are periodic (cyclically elements are periodic (cyclically repeating) functions of their atomic repeating) functions of their atomic numbernumber


MetalsMetals

to the left on the periodic tableto the left on the periodic table ductile (can be drawn into wires)ductile (can be drawn into wires) malleable (can be pounded into malleable (can be pounded into

sheets)sheets) readily conduct electricity and heatreadily conduct electricity and heat


NonmetalsNonmetals

to the right on the periodic tableto the right on the periodic table generally soft solids or gasesgenerally soft solids or gases


Classes of metalsClasses of metals

active metalsactive metals very reactive to air and watervery reactive to air and water include lithium, potassium and sodiuminclude lithium, potassium and sodium

noble metalsnoble metals very unreactivevery unreactive gold, silver and coppergold, silver and copper


MetalloidsMetalloids

elements that lie along the metal-elements that lie along the metal-nonmetal bordernonmetal border

have properties intermediate have properties intermediate between metals and nonmetalsbetween metals and nonmetals

most important current use is as most important current use is as semiconductorssemiconductors


Periodic divisionsPeriodic divisions

PeriodPeriod horizontal rows in the periodic tablehorizontal rows in the periodic table properties of elements across a period change properties of elements across a period change

dramaticallydramatically each period ends with a member of the noble each period ends with a member of the noble

gas familygas family GroupGroup

vertical columns in the periodic tablevertical columns in the periodic table properties of elements in the same group are properties of elements in the same group are

similarsimilar


Main group elementsMain group elements

Group IA - alkali metalsGroup IA - alkali metals Group IIA - alkaline earthsGroup IIA - alkaline earths Group VIA - chalcogensGroup VIA - chalcogens Group VIIA - halogensGroup VIIA - halogens Group VIIIA - noble gasesGroup VIIIA - noble gases


Transition elementsTransition elements

Group B elementsGroup B elements metals with multiple oxidation statesmetals with multiple oxidation states includes noble or coinage metals (Cu, includes noble or coinage metals (Cu,

Ag, Au)Ag, Au) platinum group metals (Ru, Rh, Pd, Os, platinum group metals (Ru, Rh, Pd, Os,

Ir, Pt)Ir, Pt) structural metals such as Fe and Crstructural metals such as Fe and Cr


Inner transition elementsInner transition elements

LanthanidesLanthanides often called rare earths due to the often called rare earths due to the

difficulty in isolating pure samplesdifficulty in isolating pure samples chemical properties almost identicalchemical properties almost identical

ActinidesActinides radioactive elements, many syntheticradioactive elements, many synthetic


Physical States of ElementsPhysical States of Elements

Reference condition is 1 atmosphere Reference condition is 1 atmosphere of pressure and 25 of pressure and 25 °C°C

Gaseous elements - HGaseous elements - H22, N, N22, O, O22, F, F22, Cl, Cl22, , noble gasesnoble gases

Liquid elements - Hg, BrLiquid elements - Hg, Br22

All other elements are solidsAll other elements are solids

Documents

Elements and Atoms Chapter Two. Wolpa/Advanced Placement Chemistry Introduction This chapter describes the origins of atomic theory, the discovery and