nuclear chemistry dhs chemistry chapters 4 and 25
Post on 28-Dec-2015
Embed Size (px)
Nuclear ChemistryDHS ChemistryChapters 4 and 25
Little House on the Prarie
Review: Structure of an Atom
Structure of an AtomAn atom consists of three types of subatomic particles, protons, neutrons, and electrons.
Structure of an AtomProtons and neutrons are located in the nucleus Electrons are in a cloud surrounding the nucleus. The number of protons is equal to the atomic number.
Structure of an AtomIf the atom is neutral, the number of electrons is equal to the number of protons.The mass number is equal to number of protons + number of neutrons.
Structure of an AtomElements with the same number of protons, but have different numbers of neutrons is called an isotope.
Structure of an Atom
Whats a chemical reaction?
Why Call it Nuclear Chemistry?See unitedstreaming.com
Chemical VS. Nuclear Nuclear reactions are caused from unstable nuclei becoming stable through radioactive decay. Releasing particles and high-energy wavesAlters the number of nuclear particles (neutrons and protons).Nuclear reactions are very different from chemical reactions.
Chemical Changes1. Occur when bonds are broken and formed.2. Atoms remain unchanged, though they may be rearranged.3. Involve only valence electrons.4. Associated with small energy changes.5. Reaction rate is influenced by temperature, pressure, concentration, and catalyst.
Nuclear Changes1. Occur when nuclei emit particles and/or rays.2. Atoms are often converted into atoms of another element. Thus their identity changes.3. May involve protons, neutrons, and electrons.4. Associated with large energy changes.5. Reaction rate is not normally affected by temperature, pressure, or catalysts.
What is an isotope?
Isotope ExamplesLithium - 6Lithium - 7Mass NumbersAtomic # = protons
IsotopesIsotopes are atoms of the same element that vary in their number of neutrons, thus they have different mass numbers.The convention for writing isotope names is first the element name dash and then the mass number.
For example: Carbon-14, carbon-12 carbon-13How many protons and neutrons does each of the isotopes of carbon have?
Carbon 148 neutrons, 6 protonsCarbon 126 neutrons, 6 protonsCarbon 137 neutrons, 6 protons
Mass Number(protons + neutrons)
More on IsotopesWhen an isotope is unstable it is called a radioisotope.To gain a more stable configuration, the nuclei emit radiation.The resulting stable atom is called the daughter product.This is called radioactive decay.
Strong Nuclear ForceThe dense nucleus has two different kinds of nuclear particles (protons + neutrons) closed packed together.The protons are positively charged nucleons.The neutrons are neutral nucleons.All of the protons in the nucleus repel each other and cause an electrostatic force that pushes the nucleus apart.
However, there is a force holding the nucleus together.The strong nuclear force is a force that acts only on subatomic particles that are extremely close together.If the strong nuclear force overcomes the electrostatic force, the nucleus stays together.
Neutron to Proton RatioThe strong nuclear force is not always strong enough to overcome the electrostatic force. When this happens the nucleus breaks apart. The stability of the nucleus can be determined by the ratio of neutrons to protons.(n/p)
Neutron to Proton RatioElements with low atomic numbers (< 20) are most stable when the neutron to proton ratio is 1:1.As the atomic number increases, more and more neutrons are needed to overcome the electrostatic force.Thus, the stable ratio of neutron to proton increases as the atomic number increases.1.5:1 is the largest ratio for a stable nucleus.
Example: Determine the neutron to proton ratio for Lead-206. Is it stable?Lead 20682 protons124 neutrons (206 82)
124 = 1.51 stable 82 1 ratio
Nuclear StabilityNeutron : ProtonsStable if: Smaller than Fe ~1 1Between Fe & Pb 1-1.5 1Bigger than Pb 1.5 1
Extra PracticeCalculate the neutron to proton ratio, and determine if the isotope is stable.
2. U- 293
2:2 1:1201:92 2.18:1124:82 1.5:1stablestableunstable
The graph on the right plots the neutrons versus protons. The band created is called the band of stability. Anything that falls outside of that band is radioactive.All elements with an atomic number greater than 83 are radioactive.
The Band of Stability
Radioactive SubstancesBananasAtomic fire ball candiesColored gemstones (blue topaz)Fiesta WareTable ware that contained unsafe amounts of radioactive UraniumUranium for color glaze. Up to 14% can be Uranium
Types of Radiation
Types of DecayNuclear reactions change an atom of one element to an atom of another element. This process is called transmutation. In a nuclear reaction there are three common types of radiation that are emitted: alpha, beta, and gamma. The first two are involved in transmutation, changing the identity of the atom.
Properties of Alpha, Beta, and Gamma RadiationPropertyAlpha()Beta ()Gamma ()CompositionAlpha particlesBeta particlesHigh-energy electromagnetic radiationDescription of RadiationHelium Nuclei
Charge2+1-0Relative Massheaviestlightest0Relative Penetrating PowerBlocked by paperBlocked by metal foilNot completely blocked by lead or concrete
Emit means to give off or release
Alpha ParticlesAlpha particles contain the same composition as a helium nucleus. Out of all of the radiation particles, alpha particles move the slowest and are the least penetrating. As a result of alpha decay, the mass number decreases by 4 and the atomic number decreases by 2.or
Beta ParticlesBeta particles are similar to an electron except they come from the unstable nucleus of the atom. Beta particles are formed and ejected when a neutron decays to a proton and an electron. The proton stays in the nucleus and the electron is the beta particle. Beta emission is a constant flow of quick moving electrons that can be stopped by a metal foil. As a result of beta decay the atomic number increases by one. The mass number does not change.
Gamma RaysGamma rays are short wavelengths (photons) that move the quickest of all the types of decay. They are very high-energy electromagnetic radiation. These rays often are released at the same time as an alpha or beta particle. The ray is the energy lost in the reaction. Gamma emission does not affect the atomic number or the mass number of the isotope.
Gamma RaysAre very dangerous!!
(write that down)
C. Gamma ( ) Emissionusually occurs along with other forms of radiation.Gamma particle is emittedNo change in mass numberNo change in atomic number
Practice Problems1. Why is radiation given off? 2. What is the most penetrating particle? 3. What is a main difference between a nuclear reaction and a chemical reaction? 4. Is Carbon-14 radioactive? Why or Why not?
III. Balancing Nuclear Reactions
Balancing Nuclear ReactionsIn nuclear reaction equations we account for all of the changes in the mass number and atomic mass that occur through the decay of the nucleus. To verify this, we include the mass number and atomic mass of every particle or atom involved in the reaction.
Solving ProblemsWhen solving/balancing a nuclear reaction, Look to find the difference of the mass numbers and atomic numbers between the reactants and the products. This will indicate the particle that was released or the atom that was formed. Make sure you have the same total mass number and atomic number on both sides of the equation.
Ex 1: Write a balanced equation for the alpha decay of polonium-210
Ex 2: Write a balanced equation for the beta decay of carbon-14
Practice Fill in the blank with the proper radiation particle or isotope1)
ExamplesEx 1. Write an equation for the alpha decay of Protactinium-231
III. Radioactive Decay Rates
Radioactive Decay RatesA.Half-LivesWe measure radioactive decay in terms of half- lives. A half life is the time it takes for half of a radioactive sample to decay.
Candy Bar BanditsThere is a candy bar left in the teachers lounge. Every 5 minutes a teacher walks in, looks at the candy bar, breaks the candy bar in half and eats it. If the candy bar originally had a mass of 20 grams, how much is left after 4 teachers have a taste?
ExampleThe half life of Carbon-14 is approximately 5730 years. If you had 12g of Carbon-14 today, in 5730 years you would only have 6g. The missing 6g decayed and turned into Nitrogen 14. And, in another 5730 years you will have 3g of Carbon-14 left and then in 5730 more years you would only have 1.5g of Carbon-14 left. Every 5730 years your sample is cut in half.
PracticeWhat is the half-life of the sample in the graph?~11 billion years
Half-LivesRatio of remaining mass to original massRemaining mass
In the boxAmount Remaining = initial amount (1/2)HL= initial amount (0.5HL)