Atomic StructureAtomic Structure

Atoms and their structureAtoms and their structureMr. BruderMr. Bruder

Dalton’s Atomic TheoryDalton’s Atomic Theory John Dalton (1766-1844) had four theoriesJohn Dalton (1766-1844) had four theories

1.1. All elements are composed of submicroscopic indivisible particles All elements are composed of submicroscopic indivisible particles called atomscalled atoms

2.2. Atoms of the same element are identical. The atoms of anyone Atoms of the same element are identical. The atoms of anyone element are different from those of any other elementelement are different from those of any other element

3.3. Atoms of different elements can physically mix together or can Atoms of different elements can physically mix together or can chemically combine w/ one another in simple whole-number ratios chemically combine w/ one another in simple whole-number ratios to form compoundsto form compounds

4.4. Chemical reactions occur when atoms are separated, joined, or Chemical reactions occur when atoms are separated, joined, or rearranged. However, atoms of one element are never changed into rearranged. However, atoms of one element are never changed into atoms of another elements as a result of a chemical reactionatoms of another elements as a result of a chemical reaction

Atoms & Subatomic ParticlesAtoms & Subatomic Particles Atom- smallest particle of an element that Atom- smallest particle of an element that

retains the properties of that elementretains the properties of that element

Gay-Lussac- under the same conditions of Gay-Lussac- under the same conditions of temperature and pressure, compounds temperature and pressure, compounds always react in whole number ratios by always react in whole number ratios by volume.volume.

Avagadro- interpreted that to mean Avagadro- interpreted that to mean at the same temperature and pressure, equal at the same temperature and pressure, equal

volumes of gas contain the same number of volumes of gas contain the same number of particlesparticles

(called Avagadro’s hypothesis)(called Avagadro’s hypothesis)

A Helpful ObservationA Helpful Observation

ElectronElectron J.J Thomson (1856-1940) – discovered the J.J Thomson (1856-1940) – discovered the

electron in 1897electron in 1897 Electron is the negative charged subatomic Electron is the negative charged subatomic

particleparticle An electron carries exactly one unit of An electron carries exactly one unit of

negative charge & its mass is 1/1840 the negative charge & its mass is 1/1840 the mass of a hydrogen atommass of a hydrogen atom

Cathode RayCathode Ray The Cathode Ray tubes pass electricity through The Cathode Ray tubes pass electricity through

a gas that is contained at a very low pressurea gas that is contained at a very low pressure

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Passing an electric current makes a beam Passing an electric current makes a beam appear to move from the negative to the appear to move from the negative to the positive endpositive end

Thomson’s ExperimentThomson’s Experiment

Voltage source

+-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field By adding an electric field

+

-

Voltage source

Thomson’s ExperimentThomson’s Experiment

By adding an electric field he found that the By adding an electric field he found that the moving pieces were negative moving pieces were negative

+

-

Thomson’s Atomic ModelThomson’s Atomic Model Thomson’s Atomic ModelThomson’s Atomic Model

Thomson though electrons were like plums Thomson though electrons were like plums embedded in a positively charged “pudding”, so embedded in a positively charged “pudding”, so his model was called the “plum pudding” modelhis model was called the “plum pudding” model

Thomsom’s ModelThomsom’s Model Found the electronFound the electron Couldn’t find Couldn’t find

positive (for a while) positive (for a while) Said the atom was Said the atom was

like plum puddinglike plum pudding A bunch of positive A bunch of positive

stuff, with the stuff, with the electrons able to be electrons able to be removed removed

Mass of ElectronMass of Electron In 1909 Robert Millikan determined the mass of an In 1909 Robert Millikan determined the mass of an

electron with his Oil Drop Experimentelectron with his Oil Drop Experiment He determined the mass to be 9.109 x 10He determined the mass to be 9.109 x 10 -31-31 kg kg The oil drop apparatusThe oil drop apparatus

Millikan’s ExperimentMillikan’s Experiment

Atomizer

Microscope

-

+

Oil

Millikan’s ExperimentMillikan’s Experiment

Oil

Atomizer

Microscope

-

+

Oil droplets

Millikan’s ExperimentMillikan’s Experiment

X-rays

X-rays give some drops a charge by knocking offelectrons

Millikan’s ExperimentMillikan’s Experiment

+

Millikan’s ExperimentMillikan’s Experiment

They put an electric charge on the plates

++

--

Millikan’s ExperimentMillikan’s Experiment

Some drops would hover

++

--

Millikan’s ExperimentMillikan’s Experiment

+

+ + + + + + +

- - - - - - -

Millikan’s ExperimentMillikan’s Experiment

Measure the drop and find volume from 4/3πr3

Find mass from M = D x V

++

--

Millikan’s ExperimentMillikan’s Experiment

From the mass of the drop and the charge on the plates, he calculated the charge on an electron

++

--

ProtonProton In 1886 Goldstein discovered the ProtonIn 1886 Goldstein discovered the Proton Proton is a positively charged subatomic Proton is a positively charged subatomic

particle found in the nucleus of a atomparticle found in the nucleus of a atom

RadioactivityRadioactivity Discovered by accidentDiscovered by accident BequerelBequerel Three types Three types

– alpha- helium nucleus (+2 charge, large alpha- helium nucleus (+2 charge, large mass)mass)

– beta- high speed electronbeta- high speed electron

– gamma- high energy lightgamma- high energy light

Ernest RutherfordErnest Rutherford Rutherford (1871-1937) proposed that all mass Rutherford (1871-1937) proposed that all mass

and all positive charges are in a small and all positive charges are in a small concentrated region at the center of the atomconcentrated region at the center of the atom

He used the Gold-Foil Experiment to prove his He used the Gold-Foil Experiment to prove his theorytheory

In 1911 he discovered the NucleusIn 1911 he discovered the Nucleus Nucleus- central core of an atom, composed of Nucleus- central core of an atom, composed of

protons and neutronsprotons and neutrons The nucleus is a positively charged region and it The nucleus is a positively charged region and it

is surrounded by electrons which occupy most is surrounded by electrons which occupy most of the volume of the atomof the volume of the atom

Rutherford’s ExperimentRutherford’s Experiment Used uranium to produce alpha particlesUsed uranium to produce alpha particles Aimed alpha particles at gold foil by Aimed alpha particles at gold foil by

drilling hole in lead blockdrilling hole in lead block Since the mass is evenly distributed in Since the mass is evenly distributed in

gold atoms alpha particles should go gold atoms alpha particles should go straight through.straight through.

Used gold foil because it could be made Used gold foil because it could be made atoms thinatoms thin

Lead block

Uranium

Gold Foil

Florescent Screen

What he expected

Because

Because, he thought the mass was evenly distributed in the atom

What he got

How he explained it

+

Atom is mostly emptyAtom is mostly empty Small dense,Small dense,

positive piecepositive piece at centerat center

Alpha particles Alpha particles are deflected byare deflected by it if it if they get closethey get close enough enough

+

Modern ViewModern View The atom is mostly The atom is mostly

empty spaceempty space Two regionsTwo regions Nucleus- protons and Nucleus- protons and

neutronsneutrons Electron cloud- region Electron cloud- region

where you have a where you have a chance of finding an chance of finding an electronelectron

NeutronNeutron James Chadwick (1891-1974) – discovered James Chadwick (1891-1974) – discovered

the neutron in 1932the neutron in 1932 Neutron is a subatomic particle with no Neutron is a subatomic particle with no

charge but their mass is nearly equal to that charge but their mass is nearly equal to that of a protonof a proton

QuarkQuark Protons & Neutrons can still be broken down Protons & Neutrons can still be broken down

into a smaller particle called the Quarkinto a smaller particle called the Quark The Quark is held together by GluonsThe Quark is held together by Gluons

Density and the AtomDensity and the Atom Since most of the particles went through, it Since most of the particles went through, it

was mostly empty.was mostly empty. Because the pieces turned so much, the Because the pieces turned so much, the

positive pieces were heavy.positive pieces were heavy. Small volume, big mass, big densitySmall volume, big mass, big density This small dense positive area is the This small dense positive area is the nucleusnucleus

Atomic ParticlesAtomic Particles

Particle Charge Mass (kg) Location

Electron -1 9.109 x 10-31 Electron cloud

Proton +1 1.673 x 10-27 Nucleus

Neutron 0 1.675 x 10-27 Nucleus

Subatomic particlesSubatomic particles

Electron

Proton

Neutron

Name Symbol ChargeRelative mass

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

SymbolsSymbols Contain the symbol of the element, the Contain the symbol of the element, the

mass number and the atomic numbermass number and the atomic number

X Massnumber

Atomicnumber

Sub-atomic ParticlesSub-atomic Particles Z - atomic number = number of protons Z - atomic number = number of protons

determines type of atomdetermines type of atom A - mass number = number of protons + A - mass number = number of protons +

neutronsneutrons Number of protons = number of electrons if Number of protons = number of electrons if

neutralneutral

SymbolsSymbols

XA

Z

Na23

11

Atomic Structure SymbolsAtomic Structure Symbols Proton = pProton = p++

Electron = eElectron = e--

Neutron = nNeutron = n00

Atomic # - SubscriptAtomic # - Subscript Mass # - SuperscriptMass # - Superscript

23592U

Rules for Atomic StructureRules for Atomic Structure1.1. Atomic # = # of ProtonsAtomic # = # of Protons

2.2. # of Protons = # of Electrons# of Protons = # of Electrons

3.3. Mass # = # of Protons + # of NeutronsMass # = # of Protons + # of Neutrons # of Neutrons = Mass # - # of Protons# of Neutrons = Mass # - # of Protons If you know the Mass # & Atomic # you If you know the Mass # & Atomic # you

know the composition of the elementknow the composition of the element

SymbolsSymbols Find the Find the

–number of protonsnumber of protons

–number of neutronsnumber of neutrons

–number of electronsnumber of electrons

–Atomic numberAtomic number

–Mass NumberMass Number

Br80 35

SymbolsSymbols if an element has an atomic if an element has an atomic

number of 34 and a mass number number of 34 and a mass number of 78 what is the of 78 what is the

–number of protonsnumber of protons

–number of neutronsnumber of neutrons

–number of electronsnumber of electrons

–Complete symbolComplete symbol

SymbolsSymbols if an element has 78 electrons and if an element has 78 electrons and

117 neutrons what is the 117 neutrons what is the

–Atomic numberAtomic number

–Mass numberMass number

–number of protonsnumber of protons

–Complete symbolComplete symbol

ExampleExample

Element Atomic #

Mass # Protons Electrons

Neutrons

K 19 19 19

11 5

16 17

46 23

35 35

IsotopesIsotopes Isotope- atoms that have the same number Isotope- atoms that have the same number

of protons but different number of neutronsof protons but different number of neutrons Since isotopes have a different number of Since isotopes have a different number of

neutrons the isotope has a different mass neutrons the isotope has a different mass number.number.

Isotopes are still chemically alike because Isotopes are still chemically alike because they have the same number of protons and they have the same number of protons and electronselectrons

Examples of IsotopesExamples of Isotopes

© 2009, Prentice-Hall, Inc.

IsotopesIsotopes

Isotopes are atoms of the same element with different Isotopes are atoms of the same element with different masses.masses.

Isotopes have different numbers of neutrons.Isotopes have different numbers of neutrons.

116C 12

6C 136C 14

6C

Naming IsotopesNaming Isotopes Put the mass number after the name of the Put the mass number after the name of the

elementelement carbon- 12carbon- 12 carbon -14carbon -14 uranium-235uranium-235

Electrical ChargesElectrical Charges Electrical charges are carried by particles of Electrical charges are carried by particles of

mattermatter Atoms have no net electrical chargesAtoms have no net electrical charges Given the number of negative charges Given the number of negative charges

combines with the number of positive combines with the number of positive charges = Electrically Neutralcharges = Electrically Neutral

All elements are Electrically NeutralAll elements are Electrically Neutral

Atomic Mass vs. Atomic WeightAtomic Mass vs. Atomic Weight Atomic Mass is for a single element Atomic Mass is for a single element Most elements are IsotopesMost elements are Isotopes How do we find their mass?How do we find their mass? We use Atomic WeightWe use Atomic Weight

Measuring Atomic MassMeasuring Atomic Mass Unit is the Atomic Mass Unit (amu)Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atomOne twelfth the mass of a carbon-12 atom Each isotope has its own atomic mass. We need Each isotope has its own atomic mass. We need

the average from the percent abundancethe average from the percent abundance Each isotope of an element has fixed mass and a Each isotope of an element has fixed mass and a

natural % abundancenatural % abundance You need both of these values to find the Atomic You need both of these values to find the Atomic

WeightWeight

Calculating Atomic WeightCalculating Atomic Weight Cl-35 34.969amu and 75.77% abundanceCl-35 34.969amu and 75.77% abundance Cl-37 36.966amu and 24.23% abundanceCl-37 36.966amu and 24.23% abundance To solve for Cl-35To solve for Cl-35

1.1. AMU x AbundanceAMU x Abundance

2.2. 34.969 x .757734.969 x .7577

3.3. = 26.496= 26.496 You solve for Cl-37You solve for Cl-37

Atomic Weight Cont.Atomic Weight Cont. Cl-37Cl-371.1. AMU x AbundanceAMU x Abundance2.2. 36.966 x .242336.966 x .24233.3. = 8.957= 8.957 Now you combine your two answersNow you combine your two answers 26.496 + 8.957=26.496 + 8.957= 35.45335.453 Look at Cl on the table. What is the Atomic Look at Cl on the table. What is the Atomic

Weight?Weight?

ExampleExample Calculate the atomic weight of copper. Calculate the atomic weight of copper.

Copper has two isotopes. One has 69.1% Copper has two isotopes. One has 69.1% and has a mass of 62.93 amu. The other has and has a mass of 62.93 amu. The other has a mass of 64.93 amu. What is the atomic a mass of 64.93 amu. What is the atomic weight???weight???

Atomic Weight & DecimalsAtomic Weight & Decimals Atomic Weight- of an element is a Atomic Weight- of an element is a

weighted average mass of the atoms in a weighted average mass of the atoms in a naturally occurring sample of an elementnaturally occurring sample of an element

Atomic Weights use decimal points because Atomic Weights use decimal points because it is an average of an elementit is an average of an element