Atomic Structure Chapter 4. Objectives –Recognize discoveries from Dalton (atomic theory), Thomson (the electron), Rutherford (the nucleus), and Bohr

Atomic StructureAtomic Structure

Chapter 4Chapter 4

ObjectivesObjectives– Recognize discoveries from Dalton (atomic Recognize discoveries from Dalton (atomic

theory), Thomson (the electron), Rutherford theory), Thomson (the electron), Rutherford (the nucleus), and Bohr (planetary model of (the nucleus), and Bohr (planetary model of atom) and understand how these discoveries atom) and understand how these discoveries lead to the modern theory. lead to the modern theory.

– Describe Rutherford’s “gold foil” experiment Describe Rutherford’s “gold foil” experiment that led to the discovery of the nuclear atom. that led to the discovery of the nuclear atom. Identify the major components (protons, Identify the major components (protons, neutrons, and electrons) of the nuclear atom neutrons, and electrons) of the nuclear atom and explain how they interact.and explain how they interact.

ObjectivesObjectives

Interpret and apply the laws of conservation of Interpret and apply the laws of conservation of mass, constant composition (definite mass, constant composition (definite proportions), and multiple proportions. proportions), and multiple proportions.

Describe how changes in the nucleus of an Describe how changes in the nucleus of an atom during a nuclear reaction result in atom during a nuclear reaction result in emission of radiation.emission of radiation.

History of the AtomHistory of the Atom

Not the history of the atom itself, but Not the history of the atom itself, but the history of the the history of the ideaidea of the atom. of the atom.

Atom DefinitionAtom Definition

AtomAtom

Smallest particle of an Smallest particle of an element that retains element that retains the chemical identity of the chemical identity of that elementthat element

Subatomic particles Subatomic particles

Electron

Proton

Neutron

Name Symbol Charge

Relative mass (amu)

Actual mass (g)

e-

p+

n0

-1

+1

0

1/1840

1

1

9.11 x 10-28

1.67 x 10-24

1.67 x 10-24

Information about Atom from Information about Atom from Periodic TablePeriodic Table

Atomic Number Avg Atomic Mass

Atomic Number and Atomic Number and Atomic MassAtomic Mass

Chemical Symbol: Chemical Symbol: abbreviation for element abbreviation for element namename

Atomic Number (Z):Atomic Number (Z): number of protons in number of protons in nucleus of atom (and electrons if neutral)nucleus of atom (and electrons if neutral)

Mass Number: Mass Number: number of protons and number of protons and number of neutrons in nucleus (whole number of neutrons in nucleus (whole number)number)

IsotopesIsotopes

Isotopes:Isotopes: atoms with the same number of atoms with the same number of protons but different number of neutronsprotons but different number of neutrons

Hyphen Notation:Hyphen Notation:– oxygen-16 and oxygen-17oxygen-16 and oxygen-17

Nuclear Symbol:Nuclear Symbol:1616

88OO 171788OO

Average Atomic MassAverage Atomic Mass

Average Atomic Mass: Average Atomic Mass: weighted average weighted average mass of atoms found in nature (decimal mass of atoms found in nature (decimal number on periodic table)number on periodic table)

Can calculate average atomic mass of Can calculate average atomic mass of elements if know percent abundance in elements if know percent abundance in nature nature

(WS Isotopes and Average Atomic Mass)(WS Isotopes and Average Atomic Mass)

Models of the AtomModels of the Atom

Dalton Model of AtomDalton Model of Atom

Small, indivisible spheresSmall, indivisible spheres

http://images.search.yahoo.com/search/images/

J.J. Thompson’s Model of AtomJ.J. Thompson’s Model of Atom Plum Pudding Model, Plum Pudding Model,

18961896 Thought an atom was Thought an atom was

like plum puddinglike plum pudding– Dough was positively Dough was positively

chargedcharged– Raisins scattered Raisins scattered

throughout the dough throughout the dough were negatively were negatively chargedcharged

– Didn’t know about Didn’t know about neutrons at this timeneutrons at this time


Rutherford’s Model of the AtomRutherford’s Model of the Atom

Rutherford Model, 1911Rutherford Model, 1911 Thought atom was Thought atom was

mostly empty spacemostly empty space– Nucleus in center is Nucleus in center is

dense, positively chargedense, positively charge– Electrons (negatively Electrons (negatively

charged) are in empty charged) are in empty space surrounding space surrounding nucleusnucleus


Bohr’s Model of the AtomBohr’s Model of the Atom

Neils Bohr, 1913Neils Bohr, 1913 Similar to Rutherford’s Similar to Rutherford’s

modelmodel Thought atom was Thought atom was

mostly empty spacemostly empty space– Nucleus in center is Nucleus in center is

dense, positively chargedense, positively charge– Electrons move in orbits Electrons move in orbits

around the nucleusaround the nucleus


(Modern) Quantum Mechanical (Modern) Quantum Mechanical Model of the AtomModel of the Atom

Heisenberg, Heisenberg, Schrodinger, many Schrodinger, many others, ~1926others, ~1926

Think atom is mostly Think atom is mostly empty spaceempty space– Nucleus in center is Nucleus in center is

dense, positively dense, positively chargecharge

– Electrons are around Electrons are around the nucleusthe nucleus

– Cannot locate location Cannot locate location of electron at specific of electron at specific timetime

http://particleadventure.org/particleadventure/frameless/modern_atom.html

Ch. 25 NuclearCh. 25 Nuclear

RadioactivityRadioactivity


Describe how changes in the nucleus of an Describe how changes in the nucleus of an atom during a nuclear reaction results in the atom during a nuclear reaction results in the emission of radiationemission of radiation

• Describe alpha, beta, and gamma particles; Describe alpha, beta, and gamma particles; discuss the properties of alpha, beta, and discuss the properties of alpha, beta, and gamma radiation; and write balanced gamma radiation; and write balanced nuclear reactions.nuclear reactions.

• Compare nuclear fission and nuclear fusion.Compare nuclear fission and nuclear fusion.


• Explain the difference between stable and Explain the difference between stable and unstable isotopes.unstable isotopes.

• Explain the concept of half-life of a Explain the concept of half-life of a radioactive element, e.g., explain why the radioactive element, e.g., explain why the half-life of C-14 has made carbon dating a half-life of C-14 has made carbon dating a powerful tool in determining the age of very powerful tool in determining the age of very old objects.old objects.

RadioactivityRadioactivity

Discovery of RadiationDiscovery of Radiation

Henri Becquerel Henri Becquerel (1896) experiment with (1896) experiment with uranium found it was emitting particlesuranium found it was emitting particles

Marie Curie Marie Curie (1898) discovered radioactive (1898) discovered radioactive element Polonium and Radiumelement Polonium and Radium

Strong Nuclear ForceStrong Nuclear Force

Opposites attract, like charges repelOpposites attract, like charges repel So why do protons stay together in nucleus?So why do protons stay together in nucleus? Strong Nuclear Force Strong Nuclear Force holds nucleus holds nucleus

together and is stronger than electrostatic together and is stronger than electrostatic repulsion between protonsrepulsion between protons– Only works over small diameterOnly works over small diameter– Neutrons help keep protons separated slightly Neutrons help keep protons separated slightly

to reduce repulsion between protonsto reduce repulsion between protons

Mass DefectMass Defect

You’d expect the mass of an atom to be the You’d expect the mass of an atom to be the sum of the individual subatomic particlessum of the individual subatomic particles44

22HeHe 2 (1.007276 amu) = 2.0145522 (1.007276 amu) = 2.014552

2 (1.008665 amu) = 2.0173302 (1.008665 amu) = 2.0173302 (0.0005486 amu) = 0.0010972 (0.0005486 amu) = 0.001097

Total = 4.032979 amuTotal = 4.032979 amu

Actual mass helium atom = 4.00268 amuActual mass helium atom = 4.00268 amu The difference between the calculated mass The difference between the calculated mass

and the actual mass is called and the actual mass is called mass defectmass defect..

Binding EnergyBinding Energy

In Einstein’s equation: E=mcIn Einstein’s equation: E=mc22 the “lost” the “lost” mass can be converted into energy mass can be converted into energy

Binding energy: Binding energy: energy released when a energy released when a nucleus is formed from protons and nucleus is formed from protons and neutronsneutrons

Could be considered as the amount of Could be considered as the amount of energy to break apart the nucleusenergy to break apart the nucleus

Associated with the strong nuclear force Associated with the strong nuclear force holding particles togetherholding particles together

Binding Energy per NucleonBinding Energy per Nucleon

RadiationRadiation

Stable nuclei have large binding energiesStable nuclei have large binding energies– High energy means it is hard for nucleus to High energy means it is hard for nucleus to

break apartbreak apart

Unstable nuclei can break apart and give off Unstable nuclei can break apart and give off particlesparticles

Radiation: Radiation: emission of energy as emission of energy as electromagnetic waves or subatomic electromagnetic waves or subatomic particlesparticles

Common Types of RadiationCommon Types of Radiation Alpha Alpha

HeHe– Helium nucleusHelium nucleus– Weak strength : can stop with Weak strength : can stop with

paperpaper Beta Beta electronelectron

ee– ElectronElectron– Medium strength: stop with Medium strength: stop with

clothingclothing Gamma Gamma

– High energyHigh energy– High energy: stop with leadHigh energy: stop with lead

mass # mass # 4, 4, Atomic # Atomic # 2 2

Mass # stays Mass # stays same, atomic # same, atomic # 11

EM wave so EM wave so mass doesn’t mass doesn’t changechange

Other Types of RadiationOther Types of Radiation

Positron Positron ee

Neutron (n)Neutron (n)nn

mass # stays mass # stays the same, the same,

Atomic # Atomic # 1 1

Mass # Mass # 1, 1, atomic # stays atomic # stays the samethe same

Nuclear EquationsNuclear Equations

2382389292 U U 234234

9090 Th + _________ Th + _________

141466 C C 1414

77 N + _________ N + _________

9944 Be + _________ Be + _________ 1212

66 C + C + 1100 n n

Answers: alpha, beta, alphaAnswers: alpha, beta, alpha

Study Buddy ReviewStudy Buddy Review

What force holds the nucleus together?What force holds the nucleus together? What is binding energy?What is binding energy? What happens when a nucleus is unstableWhat happens when a nucleus is unstable What is an alpha particle? Beta particle? What is an alpha particle? Beta particle?

Gamma radiation?Gamma radiation?

Nuclear Decay and Half LifeNuclear Decay and Half Life

DecayDecay

Radioactive decay: Radioactive decay: spontaneous emission spontaneous emission of radiation from nucleus of atomof radiation from nucleus of atom

Transmutation: Transmutation: change in the identity of an change in the identity of an element due to the emission of particles element due to the emission of particles from the nucleusfrom the nucleus

Half-LifeHalf-Life

Half-life: Half-life: time required for half of a sample time required for half of a sample of an element to decay into another of an element to decay into another elementelement

Known as rate of radioactive decayKnown as rate of radioactive decay Different for each isotopeDifferent for each isotope

A = AA = Aoo(½)(½)nn

Half Life of Some Radioactive Half Life of Some Radioactive IsotopesIsotopes

Half life of Potassium-40Half life of Potassium-40

Half-Life ProblemHalf-Life Problem

The half life of polonium-210 is 138.4 days. The half life of polonium-210 is 138.4 days. How many milligrams of polonium-210 How many milligrams of polonium-210 remain after 415.2 days if you start with 2.0 remain after 415.2 days if you start with 2.0 mg of the isotope? mg of the isotope?

Answer: 0.25 mgAnswer: 0.25 mg

Nuclear Fission and FusionNuclear Fission and Fusion

FusionFusion

Energy of our sun and other stars is Energy of our sun and other stars is produced from nuclear fusion reactionsproduced from nuclear fusion reactions

Fusion: Fusion: light massed nuclei combine to light massed nuclei combine to form a heavier, more stable nucleusform a heavier, more stable nucleus

Produces a lot of energy, also nuclear Produces a lot of energy, also nuclear wastewaste

4 4 1111 H H 44

22 He He + 2 + 2 00-1 -1 ENERGYENERGY

FissionFission

Nuclear power plants create energy from Nuclear power plants create energy from fission reactionsfission reactions

nuclear fission:nuclear fission: a heavy nucleus splits into a a heavy nucleus splits into a more stable nuclei of intermediate massmore stable nuclei of intermediate mass– energy producedenergy produced

– nuclear power plantsnuclear power plants

– Nuclear waste producedNuclear waste produced

2352359292 U + U + 11

00 n n 93933636 Kr + Kr + 140140

5656 Ba + 3 Ba + 3 1100 n + ENERGY n + ENERGY

Study Buddy ReviewStudy Buddy Review

What is half-life?What is half-life? What is radioactive decay?What is radioactive decay? Compare and contrast fusion and fission.Compare and contrast fusion and fission.

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Atomic Structure Chapter 4. Objectives –Recognize discoveries from Dalton (atomic theory), Thomson (the electron), Rutherford (the nucleus), and Bohr