atoms and their structure history of the atom n not the history of atom, but the idea of the atom n...
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Atoms and their structureAtoms and their structure
History of the atomHistory of the atom Not the history of atom, but the idea of the Not the history of atom, but the idea of the
atomatom Original idea Ancient Greece (400 B.C..)Original idea Ancient Greece (400 B.C..) Democritus and Leucippus Greek Democritus and Leucippus Greek
philosophers philosophers
History of AtomHistory of Atom Looked at beachLooked at beach Made of sandMade of sand Cut sand - smaller sandCut sand - smaller sand
Smallest possible Smallest possible piece?piece?Atomos - not to be cutAtomos - not to be cut
Another GreekAnother Greek Aristotle - Famous philosopherAristotle - Famous philosopher All substances are made of 4 elementsAll substances are made of 4 elements Fire - HotFire - Hot Air - lightAir - light Earth - cool, heavyEarth - cool, heavy Water - wetWater - wet Blend these in different proportions to Blend these in different proportions to
get all substances get all substances
Who Was Right?Who Was Right? Greek society was slave basedGreek society was slave based Beneath Famous to work with handsBeneath Famous to work with hands did not experimentdid not experiment Greeks settled disagreements by argumentGreeks settled disagreements by argument Aristotle was more famousAristotle was more famous He wonHe won His ideas carried through middle ages.His ideas carried through middle ages. Alchemists change lead to goldAlchemists change lead to gold
Who’s Next?Who’s Next? Late 1700’s - John Dalton- EnglandLate 1700’s - John Dalton- England Teacher- summarized results of his Teacher- summarized results of his
experiments and those of other’sexperiments and those of other’s In Dalton’s Atomic TheoryIn Dalton’s Atomic Theory Combined ideas of elements with that of Combined ideas of elements with that of
atomsatoms
Dalton’s Atomic TheoryDalton’s Atomic Theory All All mattermatter is made of tiny is made of tiny indivisibleindivisible
particles called atoms.particles called atoms. Atoms of the same element are identical, Atoms of the same element are identical,
those of different atoms are different.those of different atoms are different. Atoms of different elements combine in Atoms of different elements combine in
whole number ratios to form compoundswhole number ratios to form compounds Chemical reactions involve the Chemical reactions involve the
rearrangement of atoms. No new atoms rearrangement of atoms. No new atoms are created or destroyed.are created or destroyed.
Dalton’s Theory and Law of Dalton’s Theory and Law of Conservation of massConservation of mass
+
1 mas unit 4 mass units 5 mass units
5 mass units1 mass unit 4 mass units
Law of Definite Proportions (#3)Law of Definite Proportions (#3) Each compound has a specific ratio of Each compound has a specific ratio of
elementselements It is a ratio by mass It is a ratio by mass Water is always 16 grams of oxygen to 2 Water is always 16 grams of oxygen to 2
grams of hydrogengrams of hydrogen HH22O = 2 g H to 16 g O (always)O = 2 g H to 16 g O (always) HH22OO22 = 2 g H to 32 g O = 2 g H to 32 g O CO = 12 g C to 16 g OCO = 12 g C to 16 g O COCO2 2 = 12 g C to 32 g O= 12 g C to 32 g O
Law of Multiple ProportionsLaw of Multiple Proportions If two or more different compounds are If two or more different compounds are
composed of the same two elements, composed of the same two elements, the masses of the second element the masses of the second element combined with a certain mass of the combined with a certain mass of the first element can be expressed as ratios first element can be expressed as ratios of small whole numbers.of small whole numbers.
Example: HExample: H22O & HO & H22OO22
Water has 16 g O, peroxide 32 g OWater has 16 g O, peroxide 32 g O32g/16g = 1:2 ratio32g/16g = 1:2 ratio
What?What? Another example:Another example:
CO is Carbon monoxideCO is Carbon monoxide
COCO22 is Carbon dioxide is Carbon dioxide
Parts of AtomsParts of Atoms J. J. Thomson - English physicist. 1897J. J. Thomson - English physicist. 1897 Made a piece of equipment called a Made a piece of equipment called a
cathode ray tube (CRT)cathode ray tube (CRT) It is a vacuum tube - all the air has been It is a vacuum tube - all the air has been
pumped out.pumped out. Thompson pumped a pure gas at low Thompson pumped a pure gas at low
pressure into the CRTpressure into the CRT A current flows easily through a gas at A current flows easily through a gas at
low pressure. Why?low pressure. Why?
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Vacuum tube
Metal Disks
Pure gas at low pressurecathodeanode
Thomson’s ExperimentThomson’s Experiment
Voltage source
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Thomson’s ExperimentThomson’s Experiment
Voltage source
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Thomson’s ExperimentThomson’s Experiment
Voltage source
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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
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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 (cathode) appear to move from the negative (cathode) to the positive end (anode)to the positive end (anode)
Thomson’s ExperimentThomson’s Experiment
Voltage source
+-
Passing an electric current makes a beam of Passing an electric current makes a beam of light appear to move from the cathode to light appear to move from the cathode to the anodethe anode
Stream of light changed colors if he Stream of light changed colors if he changed gases. Why?changed gases. Why?
Thomson’s ExperimentThomson’s Experiment
Voltage source
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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 beam By adding an electric field he found that the beam of light took a curved path towards the positive of light took a curved path towards the positive plate.plate.
Hypothesis: Something in light has a neg chargeHypothesis: Something in light has a neg charge
+
-
cathodeAnode
Gas at low pressure
FactsFacts Different gases glow with different colors as Different gases glow with different colors as
current passes through the tubecurrent passes through the tube The part of glass tube directly opposite the The part of glass tube directly opposite the
cathode glowscathode glows An object placed between the cathode and An object placed between the cathode and
the opposite end of tube casts a shadow on the opposite end of tube casts a shadow on the glassthe glass
A paddlewheel between the electrodes rolls A paddlewheel between the electrodes rolls along on its rails from the cathode towards along on its rails from the cathode towards the anodethe anode
Thomson measured the charge/mass ratio of the negatively Thomson measured the charge/mass ratio of the negatively charged particle and found it to be very high:charged particle and found it to be very high:
charge charge massmass
1.1. If neg charged particle was in light it must be very smallIf neg charged particle was in light it must be very small2.2. Same charge to mass ratio no matter what gas was usedSame charge to mass ratio no matter what gas was used3.3. Used different types of metals for electrodes and still got Used different types of metals for electrodes and still got
the same ratiothe same ratio
How did he know the particles How did he know the particles charge was negative?charge was negative?
Thomson’s Final HypothesisThomson’s Final Hypothesis Mysterious particle is a fundamental Mysterious particle is a fundamental
part of all matterpart of all matter Smaller than the atomSmaller than the atom
Named: Named: electronelectron
What about a positive charge?What about a positive charge? Thomson wanted to find a positive particleThomson wanted to find a positive particle He repeated his experiment with a different tubeHe repeated his experiment with a different tube When the negative particles go in one direction When the negative particles go in one direction
the positive must travel the opposite waythe positive must travel the opposite way He put holes in the cathode (neg electrode) and He put holes in the cathode (neg electrode) and
the +charged particles passed through the the +charged particles passed through the holes and let off scintillations on a screen holes and let off scintillations on a screen behind the cathodebehind the cathode
He discovered the proton but not the He discovered the proton but not the location,charge, or masslocation,charge, or mass
Thomsom’s ModelThomsom’s Model Found the electronFound the electron Couldn’t find positiveCouldn’t find positive
(for a while) (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 evenly spread Mass evenly spread outout
Robert MillikanRobert Millikan Found the charge and mass on the Found the charge and mass on the
electronelectron
Handout: Oil Drop ExperimentHandout: Oil Drop Experiment
Read- answer questionsRead- answer questions
Other piecesOther pieces Proton - positively charged pieces 1840 Proton - positively charged pieces 1840
times heavier than the electrontimes heavier than the electron Neutron - no charge but the same mass Neutron - no charge but the same mass
as a proton.as a proton. Where are the pieces?Where are the pieces?
Rutherford’s experimentRutherford’s experiment Ernest Rutherford English physicist. (1910)Ernest Rutherford English physicist. (1910) Believed in the plum pudding model of the Believed in the plum pudding model of the
atom.atom. Wanted to see how big they are Wanted to see how big they are Used radioactivityUsed radioactivity Alpha particles - positively charged pieces Alpha particles - positively charged pieces
given off by uranium given off by uranium Shot them at gold foil which can be made a Shot them at gold foil which can be made a
few atoms thick few atoms thick
Rutherford’s experimentRutherford’s experiment When the alpha particles hit a florescent When the alpha particles hit a florescent
screen, it glows.screen, it glows. Here’s what it looked like (pg 72)Here’s what it looked like (pg 72)
Lead block
Uranium
Gold Foil
Florescent Screen
He ExpectedHe Expected The alpha particles to pass through The alpha particles to pass through
without changing direction very muchwithout changing direction very much BecauseBecause The positive charges were spread out The positive charges were spread out
evenly. Alone they were not enough to evenly. Alone they were not enough to stop the alpha particlesstop the alpha particles
What he expected
Because
Because, he thought the mass was evenly distributed in the atom
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 they get close it if they get close enough enough
+
Modern ViewModern View The atom is mostly The atom is mostly
empty spaceempty space Two regionsTwo regions Nucleus- protons Nucleus- protons
and neutronsand neutrons Electron cloud- Electron cloud-
region where you region where you might find an might find an electronelectron
Density and the AtomDensity and the Atom Since most of the particles went Since most of the particles went
through, it was mostly empty.through, it was mostly empty. Because the pieces turned so much, Because the pieces turned so much,
the positive pieces were heavy.the 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
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
Structure of the AtomStructure of the Atom There are two regionsThere are two regions The nucleusThe nucleus With protons and neutrons With protons and neutrons Positive chargePositive charge Almost all the massAlmost all the mass Electron cloud- Most of the volume of an Electron cloud- Most of the volume of an
atomatom The region where the electron can be The region where the electron can be
foundfound
Size of an atomSize of an atom Atoms are small.Atoms are small. Measured in picometers, 10Measured in picometers, 10-12-12 meters meters Hydrogen atom, 32 pm radiusHydrogen atom, 32 pm radius Nucleus tiny compared to atomNucleus tiny compared to atom IF the atom was the size of a stadium, the IF the atom was the size of a stadium, the
nucleus would be the size of a marble.nucleus would be the size of a marble. Radius of the nucleus near 10Radius of the nucleus near 10-15-15m.m. Density near 10Density near 101414 g/cm g/cm
Counting the PiecesCounting the Pieces Atomic Number Atomic Number = number of protons= number of protons # of protons determines kind of atom# of protons determines kind of atom the same as the number of electrons in the same as the number of electrons in
the neutral atomthe neutral atom Mass Number = Mass Number = the number of protons the number of protons
+ neutrons+ neutrons All the things with massAll the things with mass
IsotopesIsotopes Dalton was wrong.Dalton was wrong. Atoms of the same element can have Atoms of the same element can have
different numbers of neutronsdifferent numbers of neutrons different mass numbersdifferent mass numbers called called isotopesisotopes
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
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
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
F19 9
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 91 protons and if an element has 91 protons and
140 neutrons what is the 140 neutrons what is the
–Atomic numberAtomic number
–Mass numberMass number
–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
Naming IsotopesNaming Isotopes Put the mass number after the name of Put the mass number after the name of
the elementthe element carbon- 12carbon- 12 carbon -14carbon -14 uranium-235uranium-235
Atomic MassAtomic Mass How heavy is an atom of oxygen?How heavy is an atom of oxygen? There are different kinds of oxygen atoms.There are different kinds of oxygen atoms. More concerned with More concerned with average average atomic mass.atomic mass. Based on abundance of each element in Based on abundance of each element in
nature.nature. Don’t use grams because the numbers Don’t use grams because the numbers
would be too smallwould be too small
Measuring Atomic MassMeasuring Atomic Mass Unit is the Unit is the Atomic Mass Unit Atomic Mass Unit (amu)(amu) One twelfth the mass of a carbon-12 atom. One twelfth the mass of a carbon-12 atom. 12.01 amu – most abundant isotope is 12.01 amu – most abundant isotope is
carbon-12carbon-12 Other isotopes must be greater than this Other isotopes must be greater than this
because the average is over 12because the average is over 12 Each isotope has its own atomic mass we Each isotope has its own atomic mass we
need the average from percent abundance.need the average from percent abundance.
Lithium = 6.941 amuLithium = 6.941 amu– Most abundant is lithium – 7Most abundant is lithium – 7– Others are probably lower since average is Others are probably lower since average is
less than 7less than 7
– A relative measure is usually compared to A relative measure is usually compared to a known standarda known standard
– First – define the standardFirst – define the standard– *Standard for periodic table – Carbon –12 *Standard for periodic table – Carbon –12
= exactly 12.000 amu= exactly 12.000 amu
Calculating averagesCalculating averages You have five rocks, four with a mass of 50 You have five rocks, four with a mass of 50
g, and one with a mass of 60 g. What is the g, and one with a mass of 60 g. What is the average mass of the rocks?average mass of the rocks?
Total mass = 4 x 50 + 1 x 60 = 260 gTotal mass = 4 x 50 + 1 x 60 = 260 g Average mass = 4 x 50 + 1 x 60 = 260 gAverage mass = 4 x 50 + 1 x 60 = 260 g
5 5 5 5 Average mass = 4 x 50 + 1 x 60 = 260 gAverage mass = 4 x 50 + 1 x 60 = 260 g
5 5 55 5 5
Calculating averagesCalculating averages Average mass = 4 x 50 + 1 x 60 = 260 gAverage mass = 4 x 50 + 1 x 60 = 260 g
5 5 5 5 5 5 Average mass = .8 x 50 + .2 x 60Average mass = .8 x 50 + .2 x 60 80% of the rocks were 50 grams80% of the rocks were 50 grams 20% of the rocks were 60 grams20% of the rocks were 60 grams Average = % as decimal x mass + Average = % as decimal x mass +
% as decimal x mass + % as decimal x mass + % as decimal x mass + % as decimal x mass +
Atomic MassAtomic Mass Calculate the atomic mass of copper if Calculate the atomic mass of copper if
copper has two isotopes. 69.1% has a mass copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of of 62.93 amu and the rest has a mass of 64.93 amu.64.93 amu.
Atomic MassAtomic Mass Magnesium has three isotopes. 78.99% Magnesium has three isotopes. 78.99%
magnesium 24 with a mass of 23.9850 magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of amu, 10.00% magnesium 25 with a mass of 24.9858 amu, and the rest magnesium 25 24.9858 amu, and the rest magnesium 25 with a mass of 25.9826 amu. What is the with a mass of 25.9826 amu. What is the atomic mass of magnesium?atomic mass of magnesium?
If not told otherwise, the mass of the If not told otherwise, the mass of the isotope is the mass number in amu isotope is the mass number in amu
Atomic MassAtomic Mass Is not a whole number because it is an Is not a whole number because it is an
average. average. are the decimal numbers on the periodic are the decimal numbers on the periodic
table.table.
Atomic Weight/Relative Atomic Atomic Weight/Relative Atomic MassMass
12.01 amu – most abundant isotope is12.01 amu – most abundant isotope is
carbon – 12.carbon – 12.
Other isotopes of carbonOther isotopes of carbon
must be greater than thismust be greater than this
since average is over 12since average is over 12
6.941 amu6.941 amu most abundant is most abundant is 77LiLi
others are probably lowerothers are probably lower
since avg is less than 7since avg is less than 7
What is a “relative mass”?What is a “relative mass”? A relative measure is usually compared A relative measure is usually compared
to a known standard.to a known standard. 11stst – you must define the standard – you must define the standard
Standard on periodic table:Standard on periodic table:– Carbon – 12 = 12.000 amu exactlyCarbon – 12 = 12.000 amu exactly– 1 amu = 1/12 carbon-12 atom1 amu = 1/12 carbon-12 atom– 1 amu = 1.66 x 101 amu = 1.66 x 10-24-24g (mass of a g (mass of a
proton)proton)
Calculate the number of atoms in Calculate the number of atoms in 1.00794 g of H.1.00794 g of H.
Calculate the number of atoms in Calculate the number of atoms in 12.011 gram of Carbon12.011 gram of Carbon
Avogadro’s Number/The MoleAvogadro’s Number/The Mole 1 mole = 6.022 x 101 mole = 6.022 x 102323 = Avogadro’s Number = Avogadro’s Number
1 mole of H atoms = 6.022 x 101 mole of H atoms = 6.022 x 102323 atoms atoms 1 mole of C atoms = 6.022 x 101 mole of C atoms = 6.022 x 102323 atoms atoms
From periodic table:From periodic table: 1 mole of C = 12.011g1 mole of C = 12.011g 1 mole of H = 1.00794 g1 mole of H = 1.00794 g How much tells you how manyHow much tells you how many
Calculations with the moleCalculations with the mole Calculate the number of atoms of Ag in Calculate the number of atoms of Ag in
1.25 g of Ag.1.25 g of Ag.
Calculate the mass of 1,000,000 Au Calculate the mass of 1,000,000 Au atomsatoms
How about molecules?How about molecules? Remember there are some elements that Remember there are some elements that
exist as molecules aloneexist as molecules alone– Examples: The diatomic “7”Examples: The diatomic “7”
– Oxygen gasOxygen gas OO2 2 Hydrogen gas HHydrogen gas H22
– Nitrogen gasNitrogen gas NN2 2 Iodine Iodine I I22
– Flourine gasFlourine gas FF22
– Chlorine gasChlorine gas ClCl22– Bromine gasBromine gas BrBr22
ExampleExample In a sample of the air in this room there In a sample of the air in this room there
are approximately 2.33 X 10are approximately 2.33 X 102323 molecules of oxygen gas (Omolecules of oxygen gas (O22). How ). How
many moles of oxygen gas are in this many moles of oxygen gas are in this sample?sample?
More Mole FunMore Mole Fun Calculate the number of atoms in a Calculate the number of atoms in a
cube of Au that is 3 cm by 2 cm by 2cm. cube of Au that is 3 cm by 2 cm by 2cm. The density of gold is 19.3 g/cm The density of gold is 19.3 g/cm33
1 amu = 1.66 x 101 amu = 1.66 x 10-24-24 g g
How many atoms are there in 1.00794g How many atoms are there in 1.00794g of hydrogen?of hydrogen?