Unit 3 Atomic Structure
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Transcript of Unit 3 Atomic Structure
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Unit 3Atomic Structure
Chemistry IMr. Patel
SWHS
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Topic OutlineLearn Major IonsDefining the Atom (4.1)Subatomic Particles (4.2)Atomic Structure (4.2)Ions and Isotopes (4.3)Nuclear Chemistry (25.1)
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Defining the AtomAtom – the smallest particle of an
element that retains its identityCan not see with naked eyeNanoscale (10-9 m)Seen with scanning
tunneling electronmicroscope
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DemocritusDemocritus was a Greek to first
come up with idea of an atom.
His belief: atoms were indivisible and indestructible. = WRONG!
Atom comes from “atmos” - indivisible
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Dalton’s Atomic Theory2000 yrs later, John Dalton used
scientific method to transform Democritus’s idea into a scientific theory
Dalton put his conclusions together into his Atomic Theory (4 parts)
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Dalton’s Atomic Theory1. All elements are composted of tiny,
indivisible particles called atoms.
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Dalton’s Atomic Theory2. Atoms of the same element are
identical. Atoms of different elements are different
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Dalton’s Atomic Theory3. Atoms of different elements can
physically mix or chemically combine in whole number ratios.
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Dalton’s Atomic Theory4. Chemical reactions occur when
atoms are separated, joined, or rearranged. Atoms of one element can never be changed into atoms of another element due to a chemical reaction.
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The ElectronParticle with negative charge
Discovered by J.J. Thomson
Used cathode ray (electron) beam and a magnet/charged plate.
Millikan found the charge and mass
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The Proton and NeutronAn atom is electrically nuetral
If there is a negative particle then there must be positive particle
Proton – particle with positive charge
Chadwick discovered neutron – neutral charge
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Thomson’s Atomic ModelElectrons distributed in a sea of
positive chargePlum Pudding Model
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Rutherford’s Atomic ModelPerformed Gold-Foil ExperimentBeam of Alpha particles with positive
charge shot at thin piece of gold foilAlpha particles should have easily passed
through with slight deflection due to positive charge spread throughout.
Results: Most particles went straight through with no deflection. Some were deflected at large angles.
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Rutherford’s Atomic ModelThe nucleus is the central part of the
atom containing protons and neutronsPositive chargeMost of the mass
Electrons are located outside the nucleusNegative chargeMost of the volume
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Atomic Number An element is defined only by the
number of protons it contains
Atomic Number – number of protons
Number of protons = number of electronFor a neutral element
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Identify the number of Protons1. Zinc (Zn)
2. Iron (Fe)
3. Carbon (C)
4. Uranium (U)
1. 30
2. 26
3. 6
4. 92
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Mass NumberNucleus contains most of the mass
Mass Number – total protons and neutrons
Number of neutron = Mass # – Atomic #
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Identify # of Subatomic Particles1. Lithium
(MN = 7)
2. Nitrogen(MN = 14)
3. Fluorine(MN = 19)
**MN = Mass Number
1. 3 p+ , 3 e-, 4 n0
2. 7 p+ , 7 e-, 7 n0
3. 9 p+ , 9 e-, 10 n0
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Differences in Particle NumberDifferent element: different number of
protons
Ions – same number of proton, different number of electrons
Isotope – same number of proton, different number of neutronsDifferent Mass Numbers
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Two Notations for AtomsNuclear Notation
Write the element symbolOn left side, superscript = Mass NumberOn left side, subscript = Atomic Number
Isotope –Hyphen NotationWrite full name of elementOn right side, put a dashOn right side put Mass Number after dash
Hydrogen - 3
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Ex: Three isotopes of oxygen are oxygen-16, oxygen-17, and oxygen-18. Write the
nuclear symbol for each.
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Ex: Three isotopes of chromium are chromium-50, chromium-52, and chromium-53. How many neutrons are in each isotope?
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Ex: Calculate the number of neutrons for 99
42Mo.
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Atomic MassAtomic Mass Unit (amu) – one-twelfth of
the mass of the carbon-12 atom
Different isotopes have different amu (mass) and abundance (percentage of total)
Atomic Mass – weighted average mass of the naturally occurring atoms.Isotope MassIsotope Abundance
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Atomic MassBecause abundance is considered, the
most abundant isotope is typically the one with a mass number closest to the atomic mass.
Example, Boron occurs as Boron-10 and Boron-11. Periodic Table tells us Born has atomic mass of 10.81 amu.Boron-11 must be more
abundant
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Calculating Atomic MassConvert the Percent Abundance to
Relative Abundance (divide by 100)
Multiple atomic mass of each isotope by its relative abundance
Add the product (from step above) of each isotope to get overall atomic mass.
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Ex: Calculate the atomic mass for bromine. The two isotopes of bromine have atomic masses and percent abundances of 72.92 amu (50.69%) and 80.92 amu
(49.31%).
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Ex: Calculate the atomic mass for X. The four isotopes of X have atomic masses and percent abundances of 204 amu
(1.4%), 206 amu (24.1%), 207 amu (22.1%), and 208 amu (52.4%).
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Ex: Calculate the atomic mass for H. The three isotopes of H have atomic masses and percent abundances of 27
amu (85%), 26 amu (10%), and 28 amu (5%).
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Nuclear RadiationRadioactivity – nucleus emits particles
and rays (radiation)
Radioisotope – a nucleus that undergoes radioactive decay to become more stable
An unstable nucleus releases energy through radioactive decay.
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Nuclear RadiationNuclear force – the force that holds
nuclear particles together Very strong at close distances
Of all nuclei known, only a fraction are stableDepends on proton to neutron ratioThis region of stable nuclei called band
of stability
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Half LifeHalf Life – the time required for one-
half the sample to decayCan be very short
or very long
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Symbol Element Radiation Half-Life Decay Product
U-238 Uranium-238 alpha 4,460,000,
000 years Th-234
Th-234 Thorium-234 beta 24.1 days Pa-234
Pa-234 Protactinium-234 beta 1.17
minutes U-234
U-234 Uranium-234 alpha 247,000
years Th-230
Th-230 Thorium-230 alpha 80,000
years Ra-226
Ra-226 Radium-226 alpha 1,602
years Rn-222
Rn-222 Radon-222 alpha 3.82 days Po-218
Po-218 Polonium-218 alpha 3.05
minutes Pb-214
Pb-214 Lead-214 beta 27 minutes Bi-214
Bi-214 Bismuth-214 beta 19.7
minutes Po-214
Po-214 Polonium-214 alpha
1 microseco
ndPb-210
Pb-210 Lead-210 beta 22.3 years Bi-210
Bi-210 Bismuth-210 beta 5.01 days Po-210
Po-210 Polonium-210 alpha 138.4 days Pb-206
Pb-206 Lead-206 none stable (none)
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Ex: The original amount of sample was 100 g. The amount currently remaining is 25 g.
How many half-lives has gone by?
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Ex: The original amount of sample was 100 g. The amount currently remaining is 25 g after 30 minutes. What is the half life?
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Ex: The original amount of sample was 100 g. The amount currently remaining is 6.25 g. The half life
is 50 years. How much time has passed?
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Types of RadiationAlpha Radiation (Helium Atom)
Low penetrating powerPaper shielding
Beta Radiation (Electron)Moderate penetrating powerMetal foil shielding
Gamma Radiation (Pure energy)Very high penetrating powerLead/concrete shielding
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Nuclear Decay EquationsTransmutation – conversion from one element to
another through a nuclear reactionOnly occur by radioactive decayOnly when nucleus bombarded with a particle
Emissions – given offAlpha Emission, Beta Emission, Positron EmissionPositron = beta particle with a positive charge
Captures – taken inElectron Capture
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Ex: Show a Beta Emission of Copper-66.
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Ex: Show an Electron Capture of Nickel-59.
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Ex: Show a Positron Emission of Boron-8.
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Ex: Show an Alpha Emission of Thorium-232.