chapter 3 atomic structure
DESCRIPTION
Chapter 3 Atomic Structure. 3-1 Early Models of the Atom 3-2 Discovering Atomic Structure 3-3 Modern Atomic Theory 3-4 Changes in the Nucleus. 3-1 Early Models of the Atom. What are atoms? What are the postulates of Dalton’s atomic theory?. Ancient Greek – 450 BC - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 3 Atomic Structure
3-1 Early Models of the Atom3-2 Discovering Atomic Structure
3-3 Modern Atomic Theory3-4 Changes in the Nucleus
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3-1 Early Models of the AtomWhat are atoms?What are the postulates of Dalton’s atomic theory?
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Democritus
Ancient Greek – 450BCProposed that all matter is composed of
tiny, invisible particles called atomsNo one believed him during his lifetime
◦Including AristotleHis beliefs were not accepted until the 17th
and 18th centuries
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Acceptance
Was not accepted until 2 discoveries were made◦Lavoisier’s law of conservation of matter◦Joseph Louis Proust’s law of constant
composition A compound will always contain the same
proportions by mass of elements◦Water will always have 88.9% oxygen (O) and 11.1%
hydrogen (H)
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John Dalton (1766 – 1844)
English school teacherStudied past theories of atoms and laws of
matterFormed an atomic theory of matter
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Dalton’s Atomic Theory of Matter
Ea element is composed of extremely small particles called atoms
All atoms of a given element are identical, but they differ from those of any other element
Atoms are neither created/destroyed in any chem rxn
A given compound always has the same relative #s and kinds of atoms
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Atoms
The smallest particle of an element that retains the chemical identity of that element
There are 118 elements wh means there are 118 different kinds of atoms.
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Atoms
Atoms are like the words in these slides.◦If we broke it all apart, separated and organized
the letters, you would find only 26 piles.◦But by taking letters from different piles we can
create millions of very different wordsJust like words can be separated into letters,
matter can be separated into atoms.◦These separated atoms are called elements
Think of all the words you could make with the letters A, D, and M….
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Scanning Tunneling Microscope (STM)
Produces images of atomsCreated in 1981
◦Nickel Platinum
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Chemistry In Action (p93)
Consumer Tip◦“100 Percent Natural”
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Macroscopic vs Microscopic
Macroscopic – looking a the whole picture◦A tree
It is made of the leaves, branches, trunk, roots
Microscopic – the more detailed vision of an object and what makes it function◦A leaf off a tree and the little veins that carry
the nutrients through it
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Macroscopic vs Microscopic
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Chemists make their observations in the macroscopic world◦ It is the world in wh we all
live In order to understand
that world, the goal is to understand the atoms that the world is made of◦ Discoveries/Possibilities b/c
of the study of atoms Deciphering the genetic
code Designing plastics Understanding the hole in
the ozone Imprinting data on silicon
chips
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3-2 Discovering Atomic StructureHow is atomic structure related to electricity?What did cathode rays indicate about atoms?What did Rutherford conclude from his alpha-scattering experiment?
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Electric Charges
Scientists couldn’t figure out why atoms of one element acted differently than another element’s atoms
Michael Faraday (1791-1867) said that the structure of an atom was directly related to electricity
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Electric Charges
Atoms contain particles that have electrical charges
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Benjamin Franklin
An object will either have a positive or negative charge
2 like charges will repel◦ Positive w/ positive◦ Negative w/ negative
2 opposite charges will attract◦ Positive w/ negative
Franklin didn’t know where these charges came from
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Cathode Rays and Electrons
Electric current - A moving stream of electrical charges◦Electricity from wall socket or battery
Studying electrical currents provide keys to understanding electrical charges
Mid-1800s, began studying electric currents in glass tubes w/ little air
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Cathode Rays and Electrons
Tube attached on ea end to a battery◦Positive and negative
Negative = cathode Positive = anode
Radiation travels from cathode to anode◦b/c radiation came from cathode end, called
cathode ray and the tube a cathode ray tube
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Cathode Rays and Electrons
Cathode Ray tube being effected by a magnet◦http://www.youtube.com/watch?v=7YHwMWcxe
X8&feature=related
Battery
- +
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Electrons
Negative particles within the atom◦JJ Thompson (1856-1940)
Mass of 9.11 x 10 -28 gram◦0.000000000000000000000000000911 gram◦Robert Millikan (1868-1953)
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Radioactivity
Henry Becquerel (1852-1908)◦ Placed uranium on photo
paper and an image appeared
◦ Uranium was emitting radiation
Radioactivity: spontaneous emission of radiation from an element
Marie Curie and husband Pierre discovered the elements of radium and polonium were also radioactive
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The Nuclear Atom
Thompson said there were electrons in the atom (neg charge)
Why is the atom neutral then?Rutherford’s Gold Foil Experiment
◦http://www.youtube.com/watch?v=5pZj0u_XMbc◦Called this center the nucleus
Has a positive charge Very small
◦ If the atom was the size of a football stadium, the nucleus would be smaller than a dime sitting in the middle Electrons would be smaller than Franklin Roosevelt’s eye on the
dime
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The Nuclear Atomhttp://www.ndt-ed.org/EducationResources/HighSchool/Magnetism/reviewatom.htm
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How far are the electrons from the nucleus?
If the earth was the nucleus, the electrons would cover an area as large as the distance b/w the earth and nearest stars
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3-3 Modern Atomic TheoryWhat are the names and properties of the 3 subatomic particles?How can you determine the # of protons, neutrons, and electrons in an atom/ion?What is an isotope? What is atomic mass?
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Subatomic Particles
We know atoms are made from protons, neutrons, and electrons◦Recently scientists have found even smaller
particles Quarks, Gluons, Mesons, Muons, and others
◦They don’t seem to impact any Chemistry so chemists ignore Physicists study them
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The Structure of the Atom
Nucleus◦Contains the protons and neutrons
Protons = positive – p+
◦Have the same but opposite charge as electrons Neutrons = neutral/no charge – n0
Electrons ◦Negatively charged – e-
◦Move in the space outside nucleus – e- cloud◦Very small compared to p+
2000 e- = 1 p+
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Size of Subatomic Particles
Mass◦Too small for normal measurements◦Has own unit - atomic mass unit (amu)◦P+ and n0 = 1 amu, e- = 0 amu b/c so small
Length◦Diameter = 0.100 – 0.500 nanometer
Nanometer = nm = 10-9 meter◦If you drew a line across a penny (1.9 cm), you would
touch 810 million copper atoms◦If you lined up all 810 million nuclei, you would only
have a line 4 x 10-6 meter long 4 millionths of a meter
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Atomic Numbers
Henry Moseley (1887-1915)◦Student of Rutherford◦Discovered atoms of ea element contained
differ positive chargesLead to the idea that an atom’s identity
comes from the # of p+ in nucleusCall this # atomic number
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Atomic Number
The # of protonsEa element has a unique atomic #Can tell an element’s atomic # from
periodic table
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Neutral Atom
The p+ are positiveThe e- are negativeThe atom is neutralThis means, the p+ must equal the e-
◦For N, atomic # = 7 Means p+ = 7
◦Means e- = 7
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Examples
How many protons and electrons in:◦Oxygen (O)
8 p+ and e-
◦Magnesium (Mg) 12 p+ and e-
◦Silicon (Si) 14 p+ and e-
What element has 11 protons?◦Sodium
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Ions
When an atom gains/loses e-, it will have a chargeWhen an atom has a charge, called ionCharge of ion = #p+ - #e-
◦ If a magnesium atom loses 2 e-, ionic form has a charge of: #p+ - #e- = 12 – 10 = +2
◦ It is important to add the plus (+) sign into the answer Also possible to have a negative (-)
◦ Some people write the charge with the +/- after the # (2+)After you have calculated the charge, to write it
with the element symbol, add it as a subscript◦ For our magnesium example: Mg+2
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Examples
Write the chemical symbol for the ion w/:◦ 9 p+ and 10 e-
F-
◦ 13 p+ and 10 e-
Al+3
◦ 7 p+ and 10 e-
N-3
How many p+ and e- are present in:◦ S-2 ion
16 p+ and 18 e-
◦ Li+ ion 3 p+ and 2 e-
Write the chemical symbol for the ion w/:◦ 12 p+ and 10 e-
Mg+2
◦ 74 p+ and 68 e-
W+6
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Isotopes
All atoms of the same element, have the same # of p+
They may not have the same # of n0
If atoms have the same # of p+ but different # of n0 , we call them isotopes
Most elements have at least 1 isotope◦1 usually more frequent than another
In nature, it is usually a mixtureTo tell isotopes apart, we use the mass #
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Mass Number
Mass # = #p+ + #n0
◦An atom w/ 17p+ and 18n0 would have an mass # of 35 Mass # = 17 + 18 = 35
◦b/c 17 p+, tells us it is a chlorine atom Chlorine – 35
A way to write the element symbol w/ atomic and mass #s would be:
Cl3717 element symbolmass #
atomic #
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Examples
How many protons, neutrons, and electrons are in the following ions?◦ Fe+2
26 p+, 24 e-, and 30 n0
◦ Al+3
13 p+, 10 e-, and 14 n0
◦ Se-2
34 p+, 36 e-, and 45 n0
Write the complete chemical symbol for the ion w/◦ 21 p+, 24 n0, and 18 e-
Sc+3
◦ 53 p+, 74 n0, and 54 e-
I-
2656
13
27
34
79
2145
53127
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Atomic Mass
The average mass of all the isotopes of an element
Listed in the periodic table
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Practice Problems# 1-30
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3-4 Changes in the NucleusWhat changes accompany nuclear reactions?What is radioactivity?
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Nuclear Reactions
Change the composition of an atom’s nucleus
Produces alpha, beta, or gamma radiation◦Alpha and beta radiation comes from radiation
emitted from the nucleus
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Nuclear Stability
Almost all atoms have stable nuclei◦Not radioactive
Radioactivity could have harmful effects – good its rare to find in nature
Why are some more stable than others?◦# of p+ and n0 in the nucleus◦Some combinations cause instability
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Nuclear Stability
In nucleus, p+ and n0 are packed together in a very small space
How do p+ stay together in the small space if like charges repel?◦Held there by strong nuclear force
Can only be found in this situation◦Neutrons act like a net to hold the p+ in along
with the strong nuclear force
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Nuclear Stability
Pattern of stability◦Atomic # 1-20 – nuclei stable, = # of p+ and n0
◦Beyond 20 p+ - more n0 needed to keep stable◦Atomic # above 83 – radioactive nuclei
No # of n0 will make it stableAtoms unstable if too many or too few
neutrons◦Atoms w/ too many emit beta radiation
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Types of Radioactive Decay
Alpha (α)◦Alpha particles have 2 p+ and 2 n0
◦Identical to Helium – 4 nucleus◦Travel only a few cm◦Easily stopped by paper or clothing◦Usually doesn’t pose a health threat unless
actually enters the body
He42
+2 He42 α4
2
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Types of Radioactive Decay
Beta (β)◦High speed electrons (not the ones around the
nucleus)◦Comes from charges inside a nucleus◦A neutron changes into a p+ and e-
p+ stays in nucleus e- (beta particle) is propelled out of nucleus at high
speed◦100 times more penetrating than alpha
Able to penetrate 1-2 mm of solid material Able to pass through clothing and damage skin
e0-1
- e0-1 β0
-1
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Types of Radioactive Decay
Gamma (γ)◦Very energetic form of light our eyes can’t see◦Doesn’t have any particles◦More penetrating than others◦Able to penetrate deep into solid material
Body tissue◦Stopped only by heavy shielding
Concrete or lead
γ00
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When an atom emits radiation, it undergoes radioactive decay◦ Called decay b/c nucleus is decomposing to form a new
nucleusThe best way to understand the decay is w/ a
nuclear equationRa Rn α226
8822286
42+
Types of Radioactive Decay
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Partner Activity
Look at Figure 3-30 on p115 and answer the questions◦Would this protective suit protect the worker
from alpha radiation?◦Why would a person working w/ alpha radiation
also need to be concerned w/ gamma radiation?
◦Would protective clothing such as this stop gamma radiation from penetrating the worker’s skin?
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Beta decay equation
131
53 I Xe + β131
54
0
-1
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Practice Problems
Alpha decay of 79 Au
Alpha decay of 92 U
Beta decay of 11 Na
Alpha decay of 94 Pu
Alpha decay of 91 Pa
Beta decay of 87 Fr
185
238
24
242
231
233
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Chapter 3 Review
Multiple Choice◦all
True/False◦all
Concept Mastery◦(20-22, 25)
Critical Thinking and Problem Solving◦29, 31-33