Upload
rosalyn-ross
View
245
Download
5
Tags:
Embed Size (px)
Citation preview
Unit 3Atomic Structure
Chemistry IMr. Patel
SWHS
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)
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
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
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)
Dalton’s Atomic Theory1. All elements are composed of tiny,
indivisible particles called atoms.
Dalton’s Atomic Theory2. Atoms of the same element are
identical. Atoms of different elements are different
Dalton’s Atomic Theory3. Atoms of different elements can
physically mix or chemically combine in whole number ratios.
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.
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
The Proton and NeutronAn atom is electrically neutral
If there is a negative particle then there must be positive particle
Proton – particle with positive charge
Chadwick discovered neutron – neutral charge
Thomson’s Atomic ModelElectrons distributed in a sea of
positive chargePlum Pudding Model
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.
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
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
Identify the number of Protons1. Zinc (Zn)
2. Iron (Fe)
3. Carbon (C)
4. Uranium (U)
1. 30
2. 26
3. 6
4. 92
Mass NumberNucleus contains most of the massRounded Atomic MassMass Number – total protons and
neutrons
Number of neutron = Mass # – Atomic #
Identify # of Subatomic Particles
1. 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
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
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
Ex: Three isotopes of oxygen are oxygen-16, oxygen-17, and oxygen-18.
Write the nuclear symbol for each.
Ex: Three isotopes of chromium are chromium-50, chromium-52, and chromium-53. How many neutrons are in each isotope?
Ex: Calculate the number of neutrons for 99
42Mo.
Ex: Calculate the number of neutrons for 238
92U.
Ex: Classify the following atoms21
45X 2345X 20
45X.
Ex: Classify the following atoms196
79X 19580X 195
78X.
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
Atomic MassPercent Abundance – the number of desired
particles in 100 total particles of sampleAllows for comparison to any sample set
Relative Abundance – the number of desired particles in the sample usedSpecific to the sample used; not useful in
comparisonConvert % abundance to a decimal =
relative abundance
Desired particlesTotal particles in sample
% Ab = x 100%
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
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.
Ex: If there are 100 black beans, 27 pinto beans, and 173 lima beans in the container, what is the percent
abundance of the container by bean? Relative abundance?
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%).
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%).
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%).
Nuclear Radiation
Radioactivity – 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.
Nuclear Radiation
Nuclear 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
Half Life
Half Life – the time required for one-half the sample to decayCan be very short
or very long
Symbol Element Radiation Half-LifeDecay
Product
U-238Uranium-
238alpha
4,460,000,000 years
Th-234
Th-234Thorium-
234beta 24.1 days Pa-234
Pa-234Protactiniu
m-234beta
1.17 minutes
U-234
U-234Uranium-
234alpha
247,000 years
Th-230
Th-230Thorium-
230alpha
80,000 years
Ra-226
Ra-226Radium-
226alpha
1,602 years
Rn-222
Rn-222 Radon-222 alpha 3.82 days Po-218
Po-218Polonium-
218alpha
3.05 minutes
Pb-214
Pb-214 Lead-214 beta 27 minutes Bi-214
Bi-214Bismuth-
214beta
19.7 minutes
Po-214
Po-214Polonium-
214alpha
1 microseco
ndPb-210
Pb-210 Lead-210 beta 22.3 years Bi-210
Bi-210Bismuth-
210beta 5.01 days Po-210
Po-210Polonium-
210alpha 138.4 days Pb-206
Pb-206 Lead-206 none stable (none)
Ex: The original amount of sample was 100 g. The amount currently remaining is
25 g. How many half-lives has gone by?
Ex: The original amount of sample was 100 g. The amount currently remaining is 25 g after 30 minutes. What is the half life?
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?
Nuclear ReactionsDeals with nucleus
Can end up with new atoms/elements
Mass is not strictly conserved Mass DefectE = mc2
Deals with electrons
Atoms/elements remain unchanged – rearranged
Mass is strictly conserved
Nuclear vs. Chemical Reactions
Chemical Reactions
Types of Radiation
Alpha 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
Nuclear Decay Equations
Transmutation – 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
Ex: Show a Beta Emission of Copper-66.
Ex: Show an Electron Capture of Nickel-59.
Ex: Show a Positron Emission of Boron-8.
Ex: Show an Alpha Emission of Thorium-232.