Unit 2 Chapter 3 & Chapter 19 The Structure of the Atom & Nuclear Chemistry 1.
Transcript of Unit 2 Chapter 3 & Chapter 19 The Structure of the Atom & Nuclear Chemistry 1.
Unit 2
Chapter 3 & Chapter 19
The Structure of the Atom & Nuclear Chemistry
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Early Theories of Matter
Democritus (460-370 B.C.) proposed & believed that
1. Matter was not infinitely divisible
2. Made up of tiny particles called atomos
3. Atoms could not be created, destroyed, or further divided
- This sounds like the beginning of…..
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John Dalton
19th centuryDalton revised Democritus's ideas based
upon the results of scientific research he conducted
Dalton’s atomic theory
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Dalton’s Atomic TheoryElements are made of extremely small particles called
atomsAll atoms of a given element are identical
Same size, mass and chemical propertiesAtoms are indivisible in chemical processes.
They can neither be created nor destroyed in a chemical reaction
A chemical reaction simply changes the way the atom is grouped together
A compound has a constant composition of its elementsDifferent atoms combine in simple whole number
ratios to form compounds
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Dalton’s Atomic Theory
Dalton’s theory was supported by 2 Laws:
The Law of Conservation of Matter (Lavoisier)The Law of Definite or Constant Composition
(Proust)
Not all of his theory is correct!!
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What is an atom?
An atom is the smallest particle of an element that retains the properties of the element
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The Nuclear Atom
Ernest Rutherford developed a model of the atom.
His model consisted of the following ideas:An atom consists mostly of empty space through which
electrons moveElectrons are held within the atom by their attraction to
the positively charged nucleusTiny, dense region called the nucleus, which is located
in the center of the atom
Nucleus contains all of an atom’s positive charge and virtually all of its mass
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Three Subatomic Particles
Electron Proton Neutron
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Subatomic Particles in the NucleusPositively charged particles called
protonsProton’s charge: equal to but opposite that of an
electronWhy don’t the protons repel each other in the
nucleus?
Neutral particles called neutronsNeutron mass nearly equal to that of protonNeutron has no charge
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Outside the nucleusNegatively charged particles are called
electronsmove through empty space in atomNegatively charged
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Atomic Number
The number of Protons in the nucleus
Examples:Carbon (C) has 6 protons
Atomic number is 6Copper has 29 protons
Atomic number is 29
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Atomic NumberIn uncharged atom, atomic number is
also the number of electronsWhy? If an atom is charged, then it is an ion
Uncharged atom:Atomic number = # of protons = # of electrons
Take out your periodic table
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Mass Number
To find the Mass number
# protons + # neutrons
To find # neutrons mass number – proton (or atomic number)
Mass numbers are always WHOLE #’s!!
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Symbols for Atoms
X= symbol of element
A= mass number
Z= number of protons
X or XAZ
A
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Isotopes and Mass Number
C C carbon-12 carbon-13
Isotopes are atoms with the same number of protons but different number of neutrons
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Isotopes and Mass NumberExample: 3 types of Potassium
All 3 types contain 19 protons and __ electrons
# of Protons # of Neutrons Mass Number
19 20 19 21 19 22
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The End! February 2nd - Monday
Be sure to do your homework tonight!!First daily warm-up tomorrow!!
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What’s the difference between mass number and average atomic mass?
C carbon-12
But if you look on the periodic table, the number states 12.01…
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Mass of Individual Atoms
Mass of protons and neutrons:
1.67 x 10-24 g
Mass of electron is 1840 times smaller than that of protons and neutrons
9.11 x 10-28 g
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Atomic Mass Unit (amu)
Small mass #’s are not easy to work with, so the atomic mass unit (amu) was developed
One atomic mass unit (amu) is equal to 1/12 the mass of a carbon-12 atom
The mass of 1 amu is nearly equal to the mass of one proton or neutron
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Mass of Individual Atoms
Atomic mass:The weighted average mass of the isotopes of
an element
Example: ChlorineMixture of 75% chlorine-35 and 25% chlorine-37
Atomic mass = (0.75)*35 + (0.25)*37 = 35.5 amu
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What’s the difference between mass number and average atomic mass?
Mass number- specifically about one isotope
Average atomic mass- includes the masses of all the different isotopes for that atom
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The End! February 3rd - Tuesday
Go over test!Warm up practiceStart handout #2
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February 4th - Wednesday
You must complete the pre-lab questions before you can start on the labs!!
Be sure to do your homework tonight!
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Nuclear Reactions
Chemical reactionsWhat can NOT change in a chemical reaction?
Nuclear Reactions: changes that occur in the nucleus of an atom The nucleus is unstable!!
Most atoms have unstable nuclei.
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Why are some stable, while others are not?
Primary Reason:
ratio of the neutrons to the protons (n/p)
An atom is most stable when the ratio is 1:1The maximum ratio of stability is around 1.5 : 1
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Radioactivity
An unstable nucleus emits rays and particles, called radiation, to become stableThe process is called radioactivityGain stability by LOSING energy
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Radiation
Three types of radiation produced:AlphaBetaGamma
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3 Radioactive Particles
1. Alpha Particle (+)o It travels about 1/10 the speed of light (slowest)
o It is the largest, most massive particle
o It is the most dangerous if ingested
o It has the least penetrating ability - paper can stop this particle
He42
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3 Radioactive Particles
2. Beta Particle (-)o Fast accelerated electron
o Ejected when a neutron is converted to a proton in the nucleus
o Travels 1/4 the speed of light.
o It is lighter and faster than the alpha particle.
o Average penetrating ability - can be stopped by heavy clothing
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3 Radioactive Particles
3. Gamma Rayo Not really a particle; it is a form of energy from
the electromagnetic spectrum (EM)o Has no mass and no charge.o Always accompanies either beta or alpha
radiation.o Very high poweredo Travels at the speed of light.o Highest penetrating ability - can be stopped by
heavy shielding such as lead.
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Alpha Decay
An alpha particle is released A new atom is formed in the product in which:
a) the atomic number is lowered by 2
b) the mass number is lowered by 4
Example:
He42
HeRnRa 42
22286
22688
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Beta Decay
A neutron is converted in the nucleus of an atom resulting in:a) beta particle released
b) a new atom in the product whose atomic number increases by 1
c) mass number does not change
Example:
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BNC 01
147
146
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Gamma Radiation
It is the “Energy” of the reactionAlways accompanies alpha and beta
emissions.Regardless of radiation or decay,
The Law of Conservation of Matter must be observed!!
The nuclear equation must be BALANCED!!
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HeRnRa 42
22286
22688
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RADIOACTIVE PARTICLES Summary
Alpha Particle
Positive Charge
Mass of a
Helium nucleus
1/10 the speed of light
Beta particle
Negative Charge
Mass of an
electron
1/4 the speed of light
Gamma ray
No charge
No Mass
Speed of Light, c
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Half Life
The half life of a radioisotope is the time it takes for half of the sample to decay.
Half-life is represented by “t1/2”
The number of half-lives that have passed is represented by “n”
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Amount RemainingYou can use two equations, depending on
what information you have
If you have the # of half-lives that have passed..
initial amount x (1/2) n
n= # of half-lives that have passed
If you DON”T have the # of half-lives that have passed..
initial amount x (1/2) P/ t1/2
p= time that has passed
t1/2= time of half-live38
Half-life problem
If the half life element A is 3 hours and you have 90 grams of it, how many grams would be left after 9 hours?
What percent of it is remaining?
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Handout #5 Equations to AddTo find the half-life
t1/2= time passed/ # of half-lives passed
To find the # of half lives that have passed…n= time passed/ one half-life
Total time passed= n times t1/2
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Problem 3
Given informationI= 64gr= 2.0gp=12.5 hoursn=?One half-life=??
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FUSION and FISSIONFission is the splitting of nuclei
resulting in a tremendous release of energyheavy atoms split so they can become more stable
Fusion is the combining of nuclei resulting in more energy being released than fissionThe sun produces energy as a result of nuclear
fusion2 H atoms combine to form Helium
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The End! February 6th - Friday
Finish Review sheet this weekend!Review on Monday!
Change of Schedule:Do half-live lab on Monday!
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