ATOMIC MODELS

• DEMOCRITUS• LAVOISIER • DALTON• THOMPSON• MILLIKEN• RUTHERFORD

• DEMOCRITUS IS THE MAN!!!

• YOU KNOW IT!

IT’S ALL GREEK TO ME...

• WAS A GREEK PHILOSOPHER THAT BEGAN WONDERING WHAT WAS THE UNIVERSE MADE UP OF.

• HE PROPOSED THAT ALL THE MATTER IN THE UNIVERSE IS COMPOSED OF TINY PARTICLES

• THESE PARTICLES ARE INDIVISABLE• HE CALLED THESE PARTICLES

ATOMOS (MEANS INDIVISABLE)• BUT HE HAD AN OPPONENT…

DEMOCRITUS ISAN

IGNORAMUS!

ARISTOTLE WAS MUCH MORE

POPULAR AND HE OPPOSED THE IDEA

OF ATOMS!

DEMOCRITUS ISAN

IGNORAMUS!

ARISTOTLE BELIEVED THAT MATTER WAS

CONTINUOUS.

DEMOCRITUS’ ATOMS

SO...CHEMISTRY DIED FOR ABOUT 1400 YEARS

UNTIL...

SO...CHEMISTRY DIED FOR ABOUT 1400 YEARS

IN THE1700’S

• THE PREDOMINATE BELIEF BY THE MID 1700’S WAS THE MODERN DEFINITION OF AN ELEMENT AS A SUBSTANCE THAT CANNOT BE BROKEN DOWN BY ORDINARY CHEMICAL MEANS

• IT WAS ALSO BELIEVED THAT ELEMENTS COMBINE TO FORM COMPOUNDS THAT HAVE DIFFERENT PHYS AND CHEM PROPERTIES THAN THOSE OF THE ELEMENTS THAT FORM THEM.

• HOWEVER, THERE WAS CONTROVERSY AS TO WHETHER ELEMENTS ALWAYS COMBINE IN THE SAME RATIO WHEN FORMING A PARTICULAR COMPOUND.

• IN THE 1790’S, THE STUDY OF MATTER WAS REVOLUTIONIZED BY A NEW EMPHASIS ON THE QUANTITATIVE ANALYSISoSCIENTISTS’ INVESTIGATIONS WERE

MADE MORE ACCURATE BY NEW IMPROVED BALANCES

MATTER CAN BENEITHER CREATED NOR DESTROYED.

ANTOINNE LAVOISIER TOOK ADVANTAGE…

HE BEGAN TO GATHER EVIDENCE ABOUT HOW

MATTER BEHAVED BEFORE AND AFTER A

REACTION.

MATTER CAN BENEITHER CREATED NOR DESTROYED.

ANTOINNE LAVOISIER TOOK ADVANTAGE…

HE DISCOVERED THAT THE TOTAL MASS OF THE INGREDIENTS OF A

CHEMICAL REACTION WAS THE SAME AS THE TOTAL MASS OF THE RESULTS

THE LAW OF DEFINITE

PROPORTION

THE LAW OF MULTIPLE

PROPORTIONS

I’M BETTER LOOKING THAN

PROUST!

IF 2 DIFFERENT COMPDS ARE COMPOSED OF THE SAME 2

ELEMTS, THEN THE RATIO OF OF THE ELEMNTS IS ALWAYS A RATIO

OF SMALL WHOLE #’S

A CHEM COMPD IS ALWAYS COMPOSED OF THE SAME ELEM. IN

THE SAME PROPOR. BY MASS

LAW OF MULTIPLE PROPOR-

TIONS

LAW OF DEFINITE PROPOR-

TIONS + =C O CO

CARBON MONOXIDE

+ =C O CO

CARBON MONOXIDE

+ =C O CO2

CARBON DIOXIDE

+O

• IN 1808, JOHN DALTON PROPOSED AN EXPLANATION FOR THE LAW OF CONS OF MASS, THE LAW OF DEFINITE PROPORTIONS, & FORMULATED THE LAW OF MULTIPLE PROPORTIONS.

• HE REASONED THAT ELEMENTS WERE COMPOSED OF ATOMS & THAT ONLY WHOLE #’S OF ATOMS CAN COMBINE TO FORM COMPNDS

• HIS THEORY CAN BE SUMMARIZED IN 5 STATEMENTS.

1.ATOMS OF A GIVEN ELEMENT ARE IDENTICAL IN SIZE, MASS, AND OTHER PROPERTIES; ATOMS OF DIFFERENT ELEMENTS DIFFER IN SIZE, MASS, & OTHER PROPERTIES

1.ALL MATTER IS COMPOSED OF EXTREMELY SMALL PARTICLES CALLED ATOMS

ELEMENT2

ELEMENT 3

ELEMENT 1

ELEMENT4

1.IN CHEMICAL RXNS, ATOMS ARE COMBINED, SEPARATED, OR REARRANGED

1.ATOMS OF DIFFERENT ELEMENTS COMBINE IN SIMPLE WHOLE # RATIOS TO FORM CHEM COMPDS

1.ATOMS CANNOT BE SUBDIVIDED, CREATED, OR DESTROYED

+ +

DALTON AND HIS CONTEMPORARIESTHE EARLIEST THEORISTS THOUGHT THE ATOM WAS

HARD AND ROUND, MUCH LIKE TINY MARBLES

OR BALL BEARINGS.

• ALTHOUGH DALTON THOUGHT ATOMS WERE INDIVISIBLE, INVESTIGATORS IN THE LATE 1800’S PROVED OTHERWISE

• IT SOON BECAME CLEAR THAT ATOMS ARE ACTUALLY COMPOSED OF SEVERAL BASIC TYPES OF SMALLER PARTICLES

• AND IT’S THE NUMBERS AND ARRANGEMENTS OF THESE SUB-ATOMIC PARTICLES THAT DETERMINES THE IDENTITY OF THE ATOM.

• THE FIRST DISCOVERY OF A SUBATOMIC PARTICLE RESULTED FROM THE INVESTIGATIONS INTO THE RELATIONSHIP BETWEEN ELECTRICITY AND MATTER.

• IN THE LATE 1800’S, MANY EXPERIMENTS WERE PERFORMED IN WHICH ELECTRIC CURRENT WAS PASSED THROUGH VARIOUS GASES AT LOW PRESSoCARRIED OUT IN TUBES CALLED

CATHODE-RAY TUBES

• THEY HYPOTHESIZED THAT THE GLOW WAS CAUSED BY A STREAM OF PARTICLESoTHEY CALLED THE STREAM A

CATHODE RAY

• THE CATHODE RAY TRAVELED FROM THE CATHODE TO THE ANODE WHEN CURRENT WAS PASSED THROUGH THE TUBE.

• THE CATHODE RAY TUBE OPENED THE DOOR FOR J.J. THOMPSON

I PLAY WITHELECTRONS

• THOMPSON’S INVESTIGATIONS SUPPLIED EVIDENCE THAT THE CATHODE RAY COULD BE DEFLECTED BY APPLYING A POSITIVELY CHARGED ELECTRIC FIELD

• THIS HELPED THOMPSON DISC- OVER THAT THE CATHODE RAY WAS NEGATIVELY CHARGED.

• THOMPSON WAS ABLE TO MEASURE THE RATIO OF THE CHARGE OF CATHODE RAY PARTICLES TO THEIR MASSoHE FOUND THAT THE RATIO WAS THE

SAME REGARDLESS OF THE METAL USED AS THE CATHODE

• THOMPSON CONCLUDED THAT ALL CATHODE RAYS ARE COMPOSED OF IDENTICAL NEGATIVELY CHARGED PARTICLESoWHICH WERE LATER CALLED

ELECTRONS

HE PROPOSED THAT THE ATOM LOOKS SOMETHING LIKE A CHOCOLATE CHIP COOKIE

THOMPSON’S ATOMIC MODEL

THE COOKIE PART IS POS. MATTER TO

CANCEL OUT THE NEG. ELECTRONS

THE CHIPS WOULD BEHIS ELECTRONS

• THOMPSON’S EXPERIMENTS REVEALED THAT THE ELECTRON HAS A VERY LARGE CHARGE IN RELATION TO ITS MASS

• IN 1909, ROBERT MILLIKAN, PERFORMED AN INGENIOUS EXPERIMENT TO CALCULATE THE MASS OF AN ELECTRONoHE DISCOVERED THAT THE MASS OF

THE ELECTRON IS ABOUT 1/2000TH THE MASS OF THE SIMPLEST ATOM (HYDRO.)

HELLO, MILLIKANDAT’S RIGHT!I SAVED THE

DAY!

• HIS OIL DROP EXPERIMENT SHOWED THAT EVEN THOUGH THE ATOMS OF DIFFERENT ELEMENTS ARE VERY DIFFERENT, THEIR ELECTRONS ARE IDENTICAL.oAN ELECTRON IS AN ELECTRONoTHE DIFFERENCE BETWEEN TWO

DIFFERENT ATOMS IS THEIR NUMBER OF ELECTRONS NOT THEIR TYPE OF ELECTRON.

• HE ALSO CALCULATED THAT THE ELECTRON’S MASS IS 9.109x10-31kg

• THOMPSON’S & MILLIKAN’S IDEAS:o ATOMS ARE IN FACT DIVISABLEo ELECTRONS ARE PRESENT IN ATOMS OF ALL

ELEM.o ONE OF THE ATOM’S FUNDMNTL PARTICLES

IS NEG. CHARGEDo ATOMS ARE ELECTRICALLY NEUTRAL, SO

THERE MUST BE A (+) CHARGE TO BALANCE OUT THE (–)

o BECAUSE ELECTRONS ARE BASICALLY MASSLESS THERE MUST BE SOMETHING ELSE THAT ACCOUNTS FOR THE ATOMS MASS.

OTHER SIGNIFICANT DISCOVERIES…

• IN 1886, WHEN E. GOLDSTEIN OBSERVED A CATHODE-RAY TUBE AND FOUND RAYS TRAVELLING IN THE OPPOSITE DIRECTION OF THAT OF THE CATHODE RAYSoHE CALLED THE RAYS CANAL RAYS

AND CONCLUDED THAT THEY WERE COMPOSED OF POS. PARTICLES

• IT WAS SOON DISCOVERED THAT THE POSITIVE PARTICLES MASS IS ABOUT 2000 TIMES THAT OF THE ELECTRON

• IN 1932, THE ENGLISH PHYSICIST JAMES CHADWICK CONFIRMED THE EXISTANCE OF YET ANOTHER SUBATOMIC PARTICLE.oTHE NEUTRON, WHICH IS A PARTICLE

WITH NO CHARGEoHAS A MASS NEARLY EQUAL TO THAT

OF THE PROTON• THEREFORE THE SUBATOMIC

PARTICLES ARE THE ELECTRON, PROTON, AND NEUTRON.

OTHER SIGNIFICANT DISCOVERIES…

1.67x10-2410n0neutron

1.67x10-241+1p+proton

9.11x10-280-1e-electron

• WHEN SUBATOMIC PARTICLES WERE DISCOVERED, SCIENTISTS WONDERED HOW THESE PARTICLES WERE PUT TOGETHER IN AN ATOM.

• THIS WAS A DIFFICULT QUESTION TO ANSWER, GIVEN HOW TINY ATOMS ARE.

• MOST SCIENTISTS THOUGHT IT LIKELY THAT THE ELECTRONS WERE EVENLY DISTRIBUTED THROUGHOUT AN ATOM FILLED UNIFORMLY WITH POSITIVELY CHARGED MATERIAL.

THE ATOMIC NUCLEUS

ERNEST RUTHERFORDHOW IS THE

ATOM BUILT?

IN 1911, RUTHERFORD PERFORMED ONE OF THE MOST BRILLIANT

INVESTIGATIONS EVER CONCIEVED.

RUTHERFORD’S FAMOUS EXPERIMENT

• RUTHERFORD SET OUT TO TEST THE THOMPSON MODEL OF THE ATOM

• THE TEST USED RELATIVELY MASSIVE RADIOACTIVE ALPHA PARTICLESoALPHA PARTICLES () ARE HELIUM

ATOMS THAT HAVE LOST THEIR 2 ELECTRONS AND HAVE A DOUBLE POSITIVE CHARGE BECAUSE OF THE 2 REMAINING PROTONS

• IN THE EXPERIMENT, RUTHERFORD DIRECTED A NARROW BEAM OF ALPHA PARTICLES AT A VERY THIN SHEET OF GOLD FOIL.oACCORDING TO THE PREVAILING

THEORY, THE ALPHA PARTICLES SHOULD HAVE PASSED EASILY THROUGH THE GOLD, WITH ONLY A SLIGHT DEFLECTION DUE TO THE POSITIVE CHARGE THOUGHT TO BE SPREAD OUT IN THE GOLD ATOMS.

• THE MAJORITY OF THE PARTICLES PASSED STRAIGHT THROUGH THE GOLD ATOMS, WITHOUT ANY DEFLECTION

• EVEN MORE SURPRISINGLY, A SMALL FRACTION OF THE PARTICLES BOUNCED OFF THE GOLD FOIL ATOMS AT VERY LARGE ANGLES

• SOME EVEN BOUNCED BACK AT THE SOURCE

• BASED ON THE RESULTS, RUTHERFORD SUGGESTED A NEW THEORY OF THE ATOM.

• HE PROPOSED THAT THE ATOM IS MOSTLY EMPTY SPACE –THIS EXPLAINED THE LACK OF

DEFLECTION OF SOME OF THE PARTICLES

• HE CONCLUDED THAT ALL THE POSITIVE CHARGE AND ALMOST ALL THE MASS IS CONCENTRATED IN A SMALL CORE –HE CALLED THIS REGION THE

NUCLEUS

• THERE ARE THREE FUNDAMENTAL PARTICLES THAT TOGETHER MAKE UP THE ATOM.oCOMPOSED OF ELECTRONS,

PROTONS, AND NEUTRONS• THE PROTONS AND THE NEUTRONS

MAKE UP THE CENTER OF THE ATOMoCENTER OF THE ATOM IS CALLED

THE NUCLEUS• THE PROTONS & NEUTRONS OCC-

UPY THE MASS OF THE ATOM

As scientists did more experiments, they began to realize that there was something funny about protons and neutrons. In 1968 they discovered that protons and neutrons are made up of smaller particles they called quarks.

Scientists discovered six different types of quarks: Up, Down, Strange, Charm, Top and Bottom.

Protons have two Up quarks and one Down quark while neutrons have two Down quarks and one Up quark.

Quarks are held to each other by particles scientists called gluons.

STRING THEORY PROPOSES THAT THE FUNDAMENTAL PARTICLE THAT MAKES UP QUARKS IS A STRING!

STRINGS ARE SO SMALL THAT IF THEY EXIST, OUR CURRENT TECHNOLOGY WILL NOT ALLOW US TO TEST FOR THEM (WHICH SOME SCIENTISTS MAINTAIN MEANS THAT IT IS NOT A THEORY IF IT’S NOT TESTABLE)

• THE ELECTRONS SURROUND THE NUCLEUS AND OCCUPY MOST OF THE ATOM’S VOLUME/SPACE

• HOW, THEN, ARE ATOMS OF HYDROGEN DIFFERENT FROM THOSE OF OXYGEN?oA SUBATOMIC PARTICLES FROM ONE

TYPE OF ATOM LOOKS LIKE PARTICLES FROM OTHER ATOMS

• IT’S THE NUMBERS OF PROTONS IN AN ATOM THAT MAKES ATOMS DIFFERENT.oAN OXYGEN ATOM HAS 8 PROTONS IN

ITS NUCLEUSoA HYDROGEN ATOM HAS 1 PROTON IN

ITS NUCLEUS• THE ATOMIC NUMBER OF AN ELEMENT IS

THE NUMBER OF PROTONS IN THE NUCLEUS OF AN ATOM OF THAT ELEMENToSINCE OXYGEN’S NUCLEUS HAS 8

PROTONS ITS ATOMIC # IS 8• THE PROTONS IDENTIFY THE TYPE OF

ATOM, THE ONLY ATOM WITH 8 PROTONS IS OXYGEN

1020101010NeNeon9191099FFluorine816888OOxygen714777NNitrogen612666CCarbon511655BBoron49544BeBeryllium37433LiLithium24222HeHelium

ATOMS OF THE 1ST TEN ATOMS

H 1 1101Hydrogen

• FOR EACH ELEMENT LISTED, THE NUMBER OF PROTONS EQUALS THE NUMBER OF ELECTRONS (THIS ONLY WORKS FOR NEUTRAL ATOMS!)o REMEMBER ATOMS ARE ELECTRICALLY

NEUTRAL, IONS ARE CHARGED PARTICLES• IN AN ATOM, THE CHARGE IS = P - E

o A HYDROGEN ATOM HAS 1 ELECTRONo AN OXYGEN ATOM HAS 8 ELECTRONS

• THE MASS OF AN ATOM IS CONCEN. IN ITS NUCLEUS AND DEPENDS ON THE NUMBER OF PROTONS AND NEUTRONS

• THE TOTAL NUMBER OF PROTONS AND NEUTRONS IN AN ATOM IS CALLED THE MASS NUMBERoA CARBON ATOM, WHICH HAS 6

PROTONS AND 6 NEUTRONS, HAS A MASS NUMBER OF 12

• IF YOU KNOW THE ATOMIC NUMBER AND MASS NUMBER OF AN ATOM OF ANY ELEMENT, YOU CAN DETERMINE THE ATOM’S COMPOSITION

• THE COMPOSITION OF ANY ATOM CAN BE REPRESENTED IN SHORTHAND NOTATION:

Cl35

17

MASS NUMBER

ATOMIC NUMBER

NUMBER OF PROTONS

# OF PROTONS+

# OF NEUTRONS

-1

CHARGE OF THE ATOM/ION

ISOTOPES

• ISOTOPES ARE CHEMICALLY ALIKE BECAUSE THEY HAVE IDENTICAL NUMBERS OF PROTONS AND ELECTRONSo IT’S THE ELECTRONS THAT ARE

RESPONSIBLE FOR CHEMICAL BEHAVIOR

protonneutronelectron

BERYLLIUMISOTOPES

Cl35

17 Cl37

17

20 NEUTRONS

ATOMIC MASS

18 NEUTRONS

ATOMIC NUMBER

% ABUNDANCE OR % COMPOSITION =(# OF ATOMS OF ISOTOPE Z /TOTAL # OF ATOMS IN THE SAMPLE) * 100

ISOTOPIC MASS (g/atom) =

MASS OF ISOTOPE / #OF ISOTOPE ATOMS

TO CALCULATE THE MASS OF AN ELEMENT FOR THE PERIODIC TABLE, WE USE THE WEIGHTED AVE. OF THE ISOTOPES THAT EXIST FOR THAT ELEMENT

AVE. ATOMIC MASS = (MASS OF ISOTOPE 1 X % ABUNDANCE AS A DECIMAL) + (MASS OF ISOTOPE 2 X % ABUNDANCE AS A DECIMAL) + (MASS OF ISOTOPE 3 X % ABUNDANCE AS A DECIMAL) + ……

• AN ELEMENT’S ATOMS ARE NOT ALWAYS NEUTRAL IN CHARGE.o WHEN AN ATOM LOSES OR GAINS ONE OR

MORE OF ITS ELECTRONS IT BECOMES ION.• AN ION THAT HAS MORE ELECTRONS THAN

PROTONS HAS A NEGATIVE ELECTRICAL CHARGE

• AN ION THAT HAS FEWER ELECTRONS THAN PROTONS HAS A POSITIVE ELECTRICAL CHARGENOTE: IT’S THE PROTONS THAT DEFINE THE TYPE OF ATOM IT IS, BUT THE ELECTRONS DEFINE THE ATOM’S CHARGE & BEHAVIOR.

SOME ATOMS GAIN ELECTRONS

O

-

--

-

-

-

-

-

O-2

-

--

-

-

-

-

-

--

ATOM’S IONIC CHARGE = # PROTONS - # ELECTRONS

THE ACTUAL MASS OF A PROTON OR A NEUTRON IS VERY SMALL1.67x10-24 g

THE PROTONS + NEUTRONS IS THE MASS OF THE ATOM

THEREFORE THE MASS OF EVEN THE LARGEST ATOM IS INCREDIBLY SMALL

SCIENTIST’S HAVE DETERMINED THE TINY MASSES OF ATOMS BY USING AN INSTRUMENT CALLED A MASS SPECTROMETER.

• FINDING THE MASS OF AN INDIVIDUAL ATOM CAN PROVIDE USEFUL INFO, BUT IN GENERAL, THESE VALUES ARE TOO SMALL AND IMPRACTICAL TO WORK WITH.

• INSTEAD SCIENTISTS COMPARE THE RELATIVE MASSES OF ATOMS TO A REFERENCE ATOM-THE ISOTOPE CHOSEN WAS THE CARBON-12 ATOM.

oA STANDARD HAS BEEN SET THAT DEFINES THE MASS OF ALL THE OTHER ATOMS

• THIS ISOTOPE OF CARBON WAS ASSIGNED A MASS OF EXACTLY 12 ATOMIC MASS UNITS

• 1 ATOMIC MASS UNIT (amu) IS DEFINED AS 1/12TH THE MASS OF AN CARBON-12 ATOM.oUSING THAT INFORMATION WE CAN

SAY THAT A HELIUM-4 ATOM HAS A MASS 1/3 THE MASS OF C-12

• A CARBON-12 ATOM HAS 6 PROTONS AND 6 NEUTRONS IN ITS NUCLEUS, AND ITS MASS IS SET AS 12 amu.

• THE 12 PROTONS AND NEUTRONS ACCOUNT FOR NEARLY ALL OF CARBON’S MASSoTHEREFORE, THE MASS OF A SINGLE

PROTON OR A SINGLE NEUTRON HAS A MASS OF 1amu.

• SINCE THE MASS OF AN ATOM IS BASED ON INDIVIDUAL PARTICLES OF MATTER, THE ATOMIC MASS OF AN ATOM SHOULD BE A WHOLE NUMBERoYET ON THE PERIODIC TABLE THE

MASSES AREN’T WHOLE NUMBERS

THE MASSES ON THE PERIODIC TABLE ARE WEIGHTED AVERAGES

IN NATURE, MOST ELEMENTS EXIST AS A MIXTURE OF ISOTOPES

EACH ISOTOPE OF AN ELEMENT HAS A FIXED MASS AND A NATURAL ABUNDANCE.

NATURAL ABUNDANCE IS AN INDICATION OF HOW OFTEN WE WOULD ENCOUNTER A PARTICULAR ISOTOPE

ONE OF THE ISOTOPES IS ALMOST ALWAYS ENCOUNTERED MORE OFTEN SO IT GETS MORE WEIGHT

• RECALL THAT THE ELEMENT Cl HAS 2 ISOTOPES (Cl-35 & Cl-37)

• 75% OF THE CHLORINE ATOMS YOU’LL FIND IN NATURE ARE Cl-35; WHICH HAS 17 PROTONS AND 18 NEUTRONS IN ITS NUCLEUS

• 25% OF THE CHLORINE ATOMS YOU’LL FIND IN NATURE ARE Cl-37; WHICH HAS 17 PROTONS AND 20 NEUTRONS IN ITS NUCLEUS.

• SINCE WE ARE MORE LIKELY TO FIND A Cl-35 ATOM THE AVERAGE MASS OF Cl IS CLOSER TO 35 THAN TO THE TRUE AVERAGE OF 36.

• THEREFORE, THE ATOMIC MASS OF AN ATOM IS THE WEIGHTED AVERAGE MASS OF THE ATOMS IN A NATURALLY OCCURRING SAMPLE OF THE ELEMENT

• THE MASS NUMBER OF AN ATOM IS THE PROTONS + NEUTRONS OF A PARTICULAR ATOMo IF WE NEED THE MASS NUMBER

FROM THE PERIODIC TABLE WE TAKE THE CLOSEST WHOLE NUMBER TO THE ATOMIC MASS FOUND ON THE PERIODIC TABLE.

THE NUCLEUS IS HELD TOGETHER BY 2 FORCES.

ONE IS THE STRONG NUCLEAR FORCE –AN ATTRACTIVE FORCE THAT OVERCOMES THE REPULSION OF THE LIKE CHARGES OF THE PROTONS IN THE NUCLEUS- IT IS STRONG ONLY AT VERY SHORT ATOMIC DISTANCES

NEUTRONS HELP CREATE THE STRONG NUCLEAR FORCE BY ADDING A NET ATTRACTIVE FORCE TO THE NUCLEUS

FOR ELEMENTS 1-20, P USUALLY = N BEYOND ELEMENTS 20, NUCLEI NEED

INCREASINGLY GREATER N #’S > P #’S TO BE STABLE

ABOVE ATOMIC NUMBER 83, NO NUMBER OF NEUTRONS IS GREAT ENOUGH TO STABILIZE THE NUCLEUS AND ELEMENTS BECOME RADIOACTIVE

ATOMS THAT HAVE TOO MANY OR TOO FEW NEUTRONS TEND TO BE RADIOACTIVE

NUCLEI THAT CONTAIN EXCESS NEUTRONS TEND TO EMIT BETA PARTICLES WHICH OCCUR WHEN A NEUTRON IN THE NUCLEUS BREAKS DOWN INTO A PROTON AND EMITS AN ELECTRON FROM THE ATOM

PARTICLE NAME

SYMBOL

MASS OF PARTICLE

PENETRATING POWER

Alpha α Stopped by a sheet of paper

Beta Stopped by a sheet of Al foil or heavy

clothingGamma Stopped by ¼” Pb

sheeting

Alpha decay can most simply be described like this:

1) The nucleus of an atom splits into two parts.2) One of these parts (the alpha particle) goes zooming off into space.3) The nucleus left behind has its atomic number reduced by 2 and its mass number reduced by 4 (that is, by 2 protons and 2 neutrons).

Typical alpha decay:

Notice several things about it: 1) The atom on the left side is the one that splits into

two pieces & yields or produces the right side. 2) One of the two atoms on the right is ALWAYS an

alpha particle.3) The other atom on the right ALWAYS goes down

by two in the atomic number and four in the mass number.

Beta decay is somewhat more complex than alpha decay is. These points present a simplified view of what beta decay actually is:

1) A neutron inside the nucleus of an atom breaks down, changing into a proton.2) It emits an electron and an anti-neutrino (more on this later) which go zooming off into space.3) The atomic number goes UP by one and mass number remains unchanged.

Typical Beta Decay:

Some points to be made about the equation: 1) The nuclide that decays is the one on the left-hand side of the

equation.2) The order of the nuclides on the right-hand side can be in any

order.3) The way it is written above is the usual way.4) The mass number and atomic number of the antineutrino are

zero and the bar above the symbol indicates it is an anti-particle.

5) The neutrino symbol is the Greek letter "nu."

NOTE: All the atomic numbers on both sides

ADD UP TO THE SAME VALUE and the same for the mass numbers.

FISSION IS _____________________________________________________________________________________________________________________

FUSION IS

_____________________________________________________________________________________________________________________

FISSION: FUSION Fission is a nuclear

reaction in which an atomic nucleus splits, or fissions, into fragments, usually two fragments of comparable mass, with the release of large amounts of energy in the form of heat and radiation.

Small nuclei can also be combined to form a larger nucleus with an accompanying release of energy