Chapter 4

What is matter?What is matter? Matter is anything that has mass Matter is anything that has mass

and volume.and volume. Matter is made up of atoms.Matter is made up of atoms. Energy is NOT matter and does not Energy is NOT matter and does not

have mass or volume.have mass or volume. Energy and matter are related by Energy and matter are related by

E=mcE=mc22

Classifying MatterClassifying MatterH2O

Chemical vs. Physical Chemical vs. Physical PropertiesProperties

Examples of PropertiesExamples of Properties Carbon reacts with oxygen to form Carbon reacts with oxygen to form

carbon dioxide and water.carbon dioxide and water. Water boils at 100Water boils at 100ºC.ºC. Paper burns.Paper burns. A solution of KNOA solution of KNO33 is colorless. is colorless. Iron rusts.Iron rusts. Solid sulfur is dull and yellow.Solid sulfur is dull and yellow. Gold has a very high density (19.3 Gold has a very high density (19.3

g/cmg/cm33).).

Chemical vs. Physical Chemical vs. Physical ChangesChanges

Properties of matter are characteristics that Properties of matter are characteristics that can be tested or observed and are used to can be tested or observed and are used to identify matter.identify matter.

Physical properties are those which can be Physical properties are those which can be observed WITHOUT changing the chemical observed WITHOUT changing the chemical make-up of the matter.make-up of the matter.

Chemical properties can only be observed Chemical properties can only be observed when matter is involved in a chemical when matter is involved in a chemical reaction, which CHANGES the chemical reaction, which CHANGES the chemical composition.composition.

Chemical changes will create a new Chemical changes will create a new substance whereas physical changes do not.substance whereas physical changes do not.

Chemical vs. Physical Chemical vs. Physical PropertiesProperties

Compounds and DiatomicsCompounds and Diatomics Compounds are groups of atoms that are Compounds are groups of atoms that are

held together by chemical bonds.held together by chemical bonds. Compounds can be made by:Compounds can be made by:

Ionic BondingIonic Bonding: Giving and taking electrons : Giving and taking electrons (Metal-nonmetal bond)(Metal-nonmetal bond)

Covalent BondingCovalent Bonding: (Molecules) Sharing : (Molecules) Sharing electrons (nonmetal-nonmetal bond)electrons (nonmetal-nonmetal bond)

There are some gases that are bound to There are some gases that are bound to themselves as elements (the diatomics):themselves as elements (the diatomics):

Hydrogen = HHydrogen = H22 Nitrogen = N Nitrogen = N22 Oxygen = O Oxygen = O22

Fluorine = FFluorine = F22 Chlorine = Cl Chlorine = Cl22 Bromine = Br Bromine = Br22

Iodine = IIodine = I22

How are compounds different How are compounds different from mixtures?from mixtures?

A A mixturemixture is not like a is not like a compoundcompound in that in that the parts of a mixture are NOT bonded the parts of a mixture are NOT bonded together as in a pure compound.together as in a pure compound.

Examples of compounds: water (HExamples of compounds: water (H22O), O), sugar (Csugar (C66HH1212OO66), carbon dioxide (CO), carbon dioxide (CO22)…)…

Examples of mixtures: air, steel, orange Examples of mixtures: air, steel, orange juice, “Gorp” …juice, “Gorp” …

Mixtures may be Mixtures may be homogeneoushomogeneous (evenly (evenly distributed in a single phase) or distributed in a single phase) or heterogeneous heterogeneous (unevenly distributed in (unevenly distributed in different phases).different phases).

Dalton 1803 Thomson 1897

Rutherford 1909 Bohr 1913 Present Day

Atomic HistoryAtomic History The Greek philosopher The Greek philosopher DemocritusDemocritus

(400BC) coined the term (400BC) coined the term atomonatomon which which means “that which cannot be divided.”means “that which cannot be divided.”

Idea of an indivisible thing that made up Idea of an indivisible thing that made up all matter was refined by all matter was refined by colorblindcolorblind chemist chemist John DaltonJohn Dalton in 1803. in 1803. Among his Among his interests, Dalton was very interested in a interests, Dalton was very interested in a scientific explanation for his colorblindness and scientific explanation for his colorblindness and the behavior of gases.the behavior of gases.

Dalton published Dalton published five principles of matterfive principles of matter::

Dalton’s Top FiveDalton’s Top Five All matter is made of indestructible and All matter is made of indestructible and

indivisible atomsindivisible atoms. (atoms are hard, . (atoms are hard, unbreakable, and the smallest thing there is)unbreakable, and the smallest thing there is)

Atoms of a given element have identical Atoms of a given element have identical physical and chemical propertiesphysical and chemical properties. (all atoms of . (all atoms of X will behave the same anywhere)X will behave the same anywhere)

Different atoms have different propertiesDifferent atoms have different properties. (X . (X behaves differently than Y)behaves differently than Y)

Atoms combine in whole-number ratios to form Atoms combine in whole-number ratios to form compoundscompounds. (two H’s and one O = Water (H. (two H’s and one O = Water (H22O)O)

Atoms cannot be divided, created or Atoms cannot be divided, created or destroyed, destroyed, (just rearranged)(just rearranged) in chemical in chemical reactionsreactions..

These two are usually combined

Daltons Laws:Daltons Laws: Constant CompositionConstant Composition: Ratios of atoms in a compound is constant for that : Ratios of atoms in a compound is constant for that

compound. Ex: water is compound. Ex: water is ALWAYSALWAYS H H22OO Conservation of MassConservation of Mass: Mass is not created or destroyed in a chemical reaction.: Mass is not created or destroyed in a chemical reaction. Multiple ProportionsMultiple Proportions: Since atoms bond in small, whole number ratios to form : Since atoms bond in small, whole number ratios to form

compounds, compounds, their masses are small whole number ratiostheir masses are small whole number ratios. Ex: CO vs. CO. Ex: CO vs. CO22

The CRT (cathode ray The CRT (cathode ray tube)tube)

A new invention, the A new invention, the cathode ray tubecathode ray tube, ,

(c1850s) suggested the presence of (c1850s) suggested the presence of positive and positive and negative chargesnegative charges..

This suggested that atoms This suggested that atoms must be divisiblemust be divisible, and , and Dalton’s theory had to be modified.Dalton’s theory had to be modified.

In 1897, English Physicist In 1897, English Physicist J. J. ThomsonJ. J. Thomson proposed that proposed that the atom is a the atom is a sphere of positive charge with small areas sphere of positive charge with small areas of negative charge (he discovered electrons)of negative charge (he discovered electrons)..

This theory became known as the “This theory became known as the “plum puddingplum pudding” model ” model after an English “dessert” of purple bread and raisins. after an English “dessert” of purple bread and raisins.

Thomson’s cathode ray tube and plum pudding model

electron beam

Millikan’s oil experimentMillikan’s oil experiment In 1897, Thompson used electrostatics In 1897, Thompson used electrostatics

experiments to determine the charge-to-experiments to determine the charge-to-mass ratio of 1.76 x 10mass ratio of 1.76 x 1088 C/g. C/g.

Millikan’s classic oil-drop experiment Millikan’s classic oil-drop experiment allowed the charge of a single electron to allowed the charge of a single electron to be determined: 1.60 x 10be determined: 1.60 x 10-19-19 C. C.

Using these two numbers, we can Using these two numbers, we can calculate the mass of an electron:calculate the mass of an electron:

The mass of an electron is The mass of an electron is about about 1/20001/2000 of the mass of a proton! of the mass of a proton!

gxgCx

Cxmelectron

288

19

1010.9/1076.1

1060.1

Ernest RutherfordErnest Rutherford While studying radioactive elements, New While studying radioactive elements, New

Zealander Physicist Zealander Physicist Ernest RutherfordErnest Rutherford found found that radioactive alpha particles deflected that radioactive alpha particles deflected when fired at a very thin gold foil.when fired at a very thin gold foil.

This was known as the This was known as the gold foil experimentgold foil experiment, , and it suggested that the atom was not a and it suggested that the atom was not a hard sphere as thought, but was hard sphere as thought, but was mostly mostly spacespace, with a small concentration of mass., with a small concentration of mass.

This This concentration of massconcentration of mass became known became known as the as the nucleusnucleus..

Link to experiment…Link to experiment…

Rutherford’s gold foil exp. and new atomic model

The Bohr ModelThe Bohr Model A Danish physicist, A Danish physicist, Niels BohrNiels Bohr, (a student of , (a student of

Rutherford) rebuilt the model of the atom placing Rutherford) rebuilt the model of the atom placing the electrons in the electrons in energy levels (the “solar energy levels (the “solar system” model).system” model).

Bohr was one of the founders of Bohr was one of the founders of quantum physicsquantum physics – a discipline that states that energy can be given – a discipline that states that energy can be given off in small packets or off in small packets or quantaquanta of of specific sizespecific size..

Energy levels closer to the nucleus were lower in Energy levels closer to the nucleus were lower in energy than those farther away.energy than those farther away.

When a When a specific amountspecific amount of energy was added to of energy was added to an atom, an electron could jump into a higher an atom, an electron could jump into a higher energy level. energy level.

Adding the NeutronsAdding the Neutrons Although theorized by Rutherford, British Although theorized by Rutherford, British

physicist, physicist, James ChadwickJames Chadwick, proved the , proved the existence of existence of massivemassive, , neutralneutral particles. particles.

These particles came to be called These particles came to be called neutronsneutrons……

and their discovery in 1932 opened the and their discovery in 1932 opened the door for more in depth investigations into door for more in depth investigations into radioactive materials and gave the WWII radioactive materials and gave the WWII Allies the ability to enrich and purify Allies the ability to enrich and purify fissionable uranium, a necessity in the fissionable uranium, a necessity in the production of nuclear weapons.production of nuclear weapons.

The Modern ModelThe Modern Model

electron

neutron

proton

(not to scale) Chadwick’s neutrons

Rutherford’s space and nucleus

Democritus and Dalton’s atom

Bohr’s energy levels

Thompson’s electrons

Most atoms ~ 1-5 Å (Angstroms) = (1x10-10m)

What element is this? What element is this? What is is the mass of this What is is the mass of this

isotope?isotope?hey, does this proton make my MASS look big?

ElementsElements We currently know of about 110 We currently know of about 110

elements, 92 of which are naturally elements, 92 of which are naturally occurring.occurring.

We illustrate an element with an We illustrate an element with an atomic symbol.atomic symbol.

The atomic number tells the number The atomic number tells the number of protons and identifies the element.of protons and identifies the element.

The atomic mass is the total The atomic mass is the total

mass of the protons plus the mass of the protons plus the neutrons. (on the P. T. the average neutrons. (on the P. T. the average atomic mass is given)atomic mass is given)

OOXYGEN

8

15.9994

average atomic mass

atomic number

Weighted average massWeighted average mass

91.0%25.2 kg

3.0%10.0 kg

5.0%16.1 kg

? %12.0 kg

Natural Abundance - Natural Abundance - IsotopesIsotopes

There is not just one type of each atom, there are There is not just one type of each atom, there are several. When an atom has more or less several. When an atom has more or less neutronsneutrons than than another atom of the same element, we call them another atom of the same element, we call them isotopesisotopes..

For instance, the element carbon has 6 protons, but it For instance, the element carbon has 6 protons, but it could have 5, 6, 7, or 8 neutrons, to form Carbon-11, could have 5, 6, 7, or 8 neutrons, to form Carbon-11, Carbon-12, Carbon-13, and Carbon-14. Each has a Carbon-12, Carbon-13, and Carbon-14. Each has a different mass.different mass.

In nature, there is a mix of different natural isotopes. In nature, there is a mix of different natural isotopes. We use this mix to calculate We use this mix to calculate average atomic massaverage atomic mass. ex: . ex: carbon is 12.011 amucarbon is 12.011 amu

12C 13C

14C

Calculating Average Atomic Calculating Average Atomic MassMass

To find average atomic mass, we To find average atomic mass, we multiply multiply the relative abundance of an isotope by the relative abundance of an isotope by the mass of the isotopethe mass of the isotope. We then add . We then add each of the products for each isotope.each of the products for each isotope.

Example: The isotopes of element Bob Example: The isotopes of element Bob are found below:are found below:

Bob-18, 25%Bob-18, 25% Bob-19, 60%Bob-19, 60% Bob-20, 15%Bob-20, 15% What is the average atomic mass of What is the average atomic mass of

naturally occurring Bob?naturally occurring Bob?

2015.01960.01825.0 xxx

amu90.18

1amu = 1.66x10-24 grams

Avg. atomic mass/mole Avg. atomic mass/mole atomsatoms

Isotopes, Ions, and Isotopes, Ions, and Allotropes Allotropes (Oh my)(Oh my)

IsotopesIsotopes are atoms of the same element with are atoms of the same element with different different numbers of neutronsnumbers of neutrons..

IonsIons are atoms of the same element with are atoms of the same element with different different numbers of electronsnumbers of electrons. (Ions are easy to create by . (Ions are easy to create by adding or removing electrons from a neutral atom).adding or removing electrons from a neutral atom).

AllotropesAllotropes are forms of the same element, but are forms of the same element, but bonded bonded in different structuresin different structures..

Diamond and pencil graphite are examples of Diamond and pencil graphite are examples of allotropes. They are both pure carbon, but in different allotropes. They are both pure carbon, but in different structures.structures.

Isotopes and allotropesIsotopes and allotropes

IonsIons An An ionion is an atom that has is an atom that has gained or lost gained or lost

one or more electronsone or more electrons.. Recall that the Recall that the octet ruleoctet rule predicts that predicts that

atoms try to achieve atoms try to achieve zero or eight zero or eight electrons in their outer (valence) shellelectrons in their outer (valence) shell..

When an atom bonds with another atom, When an atom bonds with another atom, it it seeks to gain electrons or lose themseeks to gain electrons or lose them. . For instance:For instance:

ClCl has 7 and will has 7 and will gaingain one electron one electron Na has 1 and will Na has 1 and will loselose one electron one electron

Cl Cl-

Na Na+

Positive ions are called “cations”

Negative ions are called “anions”

Isotope symbolsIsotope symbols

Isotope symbols give the element Isotope symbols give the element symbol, the mass and atomic numbers. symbol, the mass and atomic numbers. From these, the number of protons, From these, the number of protons, neutrons, and electrons can be neutrons, and electrons can be determined.determined.

+2

a charge is shown here for an ion

PracticePractice How many protons, neutrons, and How many protons, neutrons, and

electrons are present in (a) electrons are present in (a) 2727AlAl3+3+ (b) (b) 7979SeSe2-2-

Write the isotope notation for an ion Write the isotope notation for an ion that contains 20 protons, 21 neutrons, that contains 20 protons, 21 neutrons, and 18 electrons.and 18 electrons.

Write the isotope notation for an atom Write the isotope notation for an atom of lead that has 128 neutrons.of lead that has 128 neutrons.

Write the isotope notation for the Write the isotope notation for the following:following:

Why do nuclear reactions Why do nuclear reactions occur?occur?

Nuclear reactions occur when a nucleus Nuclear reactions occur when a nucleus becomes becomes unstableunstable. .

Protons and neutrons are attracted to each Protons and neutrons are attracted to each other by the other by the strong nuclear forcestrong nuclear force. In a . In a stablestable nucleus, the attraction due to the strong force nucleus, the attraction due to the strong force is greater than the repulsion due to is greater than the repulsion due to electrostatic force. As elements get heavier, electrostatic force. As elements get heavier, they become more they become more unstableunstable. Extra neutrons . Extra neutrons must be present to the nucleus (like glue) to must be present to the nucleus (like glue) to increase stability by increasing the strong increase stability by increasing the strong force.force.

Nuclear reactions are Nuclear reactions are DIFFERENTDIFFERENT from from chemical reactions, because new elements chemical reactions, because new elements form. form.

What is radioactivity?What is radioactivity? Radioactivity is the spontaneous Radioactivity is the spontaneous

emission of radiation from an element emission of radiation from an element to achieve a more stable state. to achieve a more stable state.

Uranium was the first radioactive Uranium was the first radioactive element isolated (by Bequerel), followed element isolated (by Bequerel), followed by radium and polonium (by Marie Curie by radium and polonium (by Marie Curie and her husband Pierre).and her husband Pierre).

There are no stable isotopes for There are no stable isotopes for elements after Bismuth (#83).elements after Bismuth (#83).

Types of RadiationTypes of Radiation

NameName SymbolsSymbols ChargeCharge MassMass

AlphaAlpha αα or or 4422HeHe +2+2 44

BetaBeta ββ or or 00-1-1ee -1-1 00

gammagamma γγ 00 00

Nuclear ReactionsNuclear Reactions Nuclear reactions Nuclear reactions change the compositionchange the composition of of

an atom’s nucleus –the element will change!!an atom’s nucleus –the element will change!! Examples of naturally occurring nuclear Examples of naturally occurring nuclear

reactions include alpha and beta decay, and reactions include alpha and beta decay, and fission and fusion.fission and fusion.

Some nuclei can become unstable by Some nuclei can become unstable by artificial transmutationartificial transmutation, where a nucleus is , where a nucleus is bombarded (or shot) with a particle that bombarded (or shot) with a particle that creates instability and causes radioactive creates instability and causes radioactive decay. decay.

Nuclear reactions can produce enormous Nuclear reactions can produce enormous amounts of amounts of energyenergy as nuclear mass is as nuclear mass is converted into energy (E=mcconverted into energy (E=mc22))

Radioactive Decay Radioactive Decay EquationsEquations

Alpha decay equation.Alpha decay equation.

Beta decay equation.Beta decay equation.

Gamma decay involves Gamma decay involves energy transitions energy transitions (electromagnetic waves), no (electromagnetic waves), no particles are lost.particles are lost.

parent isotope daughter isotope

nuclear fission

Other nuclear reactions….fusion

and fission

21H + 3

1H→ 42He + 1

0n

23592U + 1

0n→ 9038Sr + 143

54Xe + 310n

Nuclear Reactor DesignNuclear Reactor Design

Nuclear AccidentsNuclear AccidentsChernobylHiroshima and

Nagasaki

Three Mile Island

Products of Nuclear Products of Nuclear ReactionsReactions

In nuclear reactions, unstable nuclei In nuclear reactions, unstable nuclei change their number of protons and change their number of protons and neutrons.neutrons.

A A DIFFERENTDIFFERENT element is created by the element is created by the reaction, and large amounts of energy reaction, and large amounts of energy are released (E=mcare released (E=mc22), much more than ), much more than in a chemical reaction.in a chemical reaction.

Nuclear reactions result in the Nuclear reactions result in the production of new, more stable nuclei. production of new, more stable nuclei. Unstable nuclei will continue to decay Unstable nuclei will continue to decay until a stable isotope is produced.until a stable isotope is produced.

Radioactive Decay Series

A decay series ends with a stable isotope.

Radioactive decay and Radioactive decay and half-lifehalf-life

conc

entr

atio

n

Nevada Nuclear Testing -Nevada Nuclear Testing -1950’s1950’s

The Radium GirlsThe Radium GirlsThe The Radium GirlsRadium Girls were women were women

subjected to radiation subjected to radiation exposure at the United States exposure at the United States Radium Corporation factory, Radium Corporation factory, in Orange, New Jersey around in Orange, New Jersey around 1917. These women painted 1917. These women painted the dials of watch faces with the dials of watch faces with luminous paint and luminous paint and developed cancer (typically developed cancer (typically of the mouth and jaw) as a of the mouth and jaw) as a result.result.For fun, the Radium Girls painted their nails, teeth and faces with the deadly paint

produced at the factory, sometimes to surprise their boyfriends when the lights went out. They mixed glue, water and radium powder, and then used camel hair brushes to apply the glowing paint onto dial numbers. The going rate, for painting 250 dials a day, was about a penny and a half per dial. The brushes would lose shape after a few strokes, so the U.S. Radium supervisors encouraged their workers to point the brushes with their lips, or use their tongues to keep them sharp.

THE ENDTHE END

It is disconcerting to reflect on the It is disconcerting to reflect on the number of students we have number of students we have flunked in chemistry for not flunked in chemistry for not knowing what we later found to be knowing what we later found to be untrue.untrue.

– Quoted in Robert L. Weber, – Quoted in Robert L. Weber, Science With a Smile (1992) Science With a Smile (1992)

Erwin Schrodinger Erwin Schrodinger (1887-1961)(1887-1961)

Blame me! I Blame me! I

started all of this! started all of this!

In 1926 I described In 1926 I described

the location and the location and

energy of electrons energy of electrons

in an atom with my in an atom with my

mathematical mathematical

model.model.

Hi