Atomic Structure & Theory Atomic Structure & Theory
Atomic Structure & Theory Atomic Structure & Theory Notes The The Natural world is Understandable Science Demands Evidence Science is a Blend of Logic & Imagination Scientific Knowledge is Durable
Nature of Science Theory = used to explain complex natural processes. Scientific Law = often use mathematical formulas to show relationships and make predictions about the natural world. A description of what happens. Subject to Change Scientists Attempt to Avoid Bias Science is a complex social activity. Scientific Method Question/Problem/Observation Hypothesis an EDUCATED Guess proposed reason for what is observed Experiment
To test hypothesis. Create a controlled experiment with one experimental variable, constants, and controls. Quantitative Data = numeric data. Qualitative Data = nonnumeric data. Analyze Data Create Graphs, Perform calculations Etc. Conclusion Compare experimental results with hypothesis. Create a new hypothesis. Observation Hypothesis
Experiment Law Non linear nature of science video Theory Observation Versus Inference An observation is the gathering of information by using our five senses: sight, smell, hearing, taste, touch
Qualitative- Quality = descriptive Ex. The shirt is blue. Quantitative- Quantity = numerical Ex. The flower has 7 petals. An inference is something a scientist thinks is true, based on observations or evidence. They are based on your past experiences and prior knowledge. Inferences often change when new observations are made. Examples: Observation vs Inference Examples: Observation: The grass on the playground is wet. Possible inferences: It
rained. The sprinkler was on. There is morning dew on the grass. Observation: The line at the water fountain is long. Possible inferences: It's hot outside. The students just came in from EARLY MODELS Of THE ATOM I. The Greek Philosophers A. Around 450 BC a Greek philosopher, Democritus proposed the all matter is actually composed of tiny, indivisible particles, which he called atomos. B.
At the same time Aristotle and other philosophers did not agree. They thought that if matter were made up of tiny particles it would fall apart. Aristotle's view made more sense at the time, so it prevailed for 21 centuries. II. Late 1700's A. Law of Conservation of Matter (Antoine Lavoisier) Matter can neither be created nor destroyed in a chemical reaction Example: 16 X + 8 Y 8YX2 Mass Mass Atoms Atoms
B. Law of Constant Composition A given compound always contains the same elements in the same proportions by mass. Example: H2O is always 11.1 % hydrogen and 88.9 % oxygen; no matter how much water there is. Same proportions of H & O Same proportions of H & O (by mass)
Now thats High Quality H2O C.Law of Multiple Proportions -Applies to different compounds made from the same elements. -The mass ratio for one of the elements that combines with a fixed mass of the other element can be expressed in small whole #s Examples: H2O : 2 H + 1 O (2:1) H2O2 : 2 H + 2 O (2:2) Summary of John Dalton's Atomic Theory (180
1) Each element is composed of extremely small particles called atoms, which are identical in their chemical properties. 2) All atoms of a given element are identical, but they differ from those of any other element. 3) Atoms of different elements combine in simple whole number ratios to form chemical compounds. 4) Atoms are neither created nor destroyed when they are combined, separated or
rearranged in a chemical reaction. Dalton's Model of the Atom (1803) Solid Sphere Model. Nothing smaller = no subatomic particles JJ Thomson's Model Experimented with cathode rays He concluded that there were negatively charged particles he called electrons. The "Plum Pudding" or "Raisin Bun" model. Like a ball of chocolate chip cookie dough.Choc. Chips = electronsDough = positive charge Raisins (electrons) dispersed throughout positive dough. Skip Picture
Back Plum Pudding Model raisins = eSoft pudding-like dough = positive charge The Charge on the electron Robert Millikan discovered the numerical charge on the electron using the oil drop experiment
Lord Ernest Rutherford's Model (1909) Gold Foil experiment When Rutherford directed a beam of positive particles at a thin gold foil, most of the particles passed through unaffected, but a small fraction deflected in all directions. The small number that were deflected indicated that most of the atom was empty space. Rutherford concluded that the positive charge of the atom was concentrated in a small compact nucleus. Back to Rutherford Rutherfords Experiment Back to Rutherford
Rutherfords experiment Back to Rutherford Nuclear Model Model called the "Nuclear atom" Positive charge concentrated in the nucleus, w/ e- moving around it. Atom is mostly empty space Positive Particles in nucleus later called protons If this dot were the nucleus of an atom, the atom would have the diameter of a football field. The nucleus is very tiny compared with the rest of the atom. Discovery of the Neutron
James Chadwick (1932) discovered a particle with no charge and a mass equal to a proton-he called it a neutron. Neils Bohr Planetary MODEL Experimented on Hydrogen proposed that e- in an atom can reside only in certain energy levels or orbitals The rungs on a ladder are similar to the energy levels within an atom. A person can move up or down the ladder only by standing on its rungs; it is impossible to stand
between them Planetary Model e- e- ee- ee- ee- ee- Nucleus (p+ & n0) Concentric Circular orbits Cloud Model
Particles in an Atom Particle Symbol Charge Mass (AMU) Electron e- -1 0 Proton
p+ +1 1 Neutron n0 0 1 Element = made of one kind of Atom. Compounds = made of different atoms combined in whole number ratios. Mixtures are physical combinations of elements or compounds with variable composition.
What holds nucleus together? Nuclear Tug-Of-War Electrostatic force like charges repel and unlike charges attract + + + Strong Nuclear Force holds nucleons (p+ & n0) together, very strong nuclear force but over short distances Stable nuclei are SMALL Large nuclei tend to be unstable (radioactive)
Where do Atoms Come From? Fusion = smaller atoms combine to form larger atoms (stars & supernovas) Fission = large atoms split (atomic bombs, nuclear reactors) Why dont electrons fly off? Electrostatic Holds Force
electrons on atom Nuclear Pull: + nucleus pulls electrons towards itself. More charge = more attraction Increases Counting Particles in Atoms Notes Atomic Number = (smaller #) = # of p+ = unique for each element Atomic Mass Number = mass of an atom = p+ & n (e- have no mass)
Complete heavy atomic Mass Shorthand Symbol top Sym Atomic # Example: Counting e Atoms are neutral so, p+ = e(assume an atom is neutral unless a charge is written) Ions = charged atoms (lost or gained e-) (charge in upper right hand corner )
Cation = positive atom (lost e-) Anion = negative atom (gained e-) Neutrons Isotopes = atoms of the same element with diff. numbers of n and atomic masses Sym-mass 13 U-235 H-3 C-14 C 6
The number is the atomic mass Formulas: # of p+ = Atomic Number # of n = Atomic Mass Atomic Number # of e- = Atomic Number charge Examples: 35 Cl 1 17 Mg+2 19 F
9 1 Average Atomic Mass All masses are based on the mass of C = 12 amu (atomic mass unit) Relative to Carbon Relative Atomic Mass Use mass spectrometer
Average Atomic Mass Weighted average of the masses of the isotopes of that element Reflects relative abundance of isotopes in nature Problem #1: Carbon To calculate the average atomic weight, each exact atomic weight is multiplied by its percent abundance (expressed as a decimal). Then, add the results together and round off to an appropriate number of significant figures. mass number exact weight percent abundance
12 12.000000 98.90 13 13.003355 1.10 This is the solution for carbon: (12.000000) (0.9890) + (13.003355) (0.0110) = 12.011 amu . Average Atomic Mass =
types of atoms spontaneously change because they are unstable. They eject sub particles or emit energy and are transformed into different types of atoms. Atoms that are changed in this way are called radioactive, and the transformation process is called radioactive decay. Products of Decay Natural Decay Products - there are three major products emitted by the decay of naturally occurring radioactive isotopes.
Alpha particles () Beta particles (- & +) Gamma ray ()) Radiation Radiation Interaction and Penetration Through Matter alpha High charge, dense ionization, short path beta Less mass/charge than alpha, longer path alpha gamma No charge or mass, much less interaction
neutron No charge, interacts through nuclear events Not to scale Alpha Alpha Particle Particle aa Characteristics Range Shielding Hazards Sources +2 charge 2 protons
2 neutrons Large mass Very short range 1" -2" in air Paper Outer layer of skin Internal Plutonium Uranium Radium Thorium Americium a a
a a a Beta Beta Particle Particle bb Characteristics Range -1 charge Small mass Shielding Short range Plastic safety glasses About 10'
in air Thin metal Hazards Sources Skin and eyes Radioisotopes Can be internal Activation Products Sealed sources
Gamma Gamma Ray Ray gg Characteristics Range Shielding No charge No mass Similar to x-rays External Lead Steel (whole body) Concrete Can be internal
Long range About 1100' in air Paper Plastic Lead Hazards Sources X-ray machines Electron microscopes Sealed sources Accelerators Nuclear reactors Radioisotopes
Neutron Neutron Particle Particle hh Characteristics Range No charge Found in nucleus Extended range Shielding Hazards Sources Water Plastic
External (whole body) Fission Reactor operation Sealed sources Accelerators Paper Lead Water Half Life Half Life = (t1/2) The amount of time it takes for of the radioactive isotope to decay (no longer therechanged into something else.
Multiply the mass by for each life that passes (or divide by 2) Estimating the AGE of Materials Radioactive carbon-14 atoms are used to estimate the age of materials that were once living. Living things all have the same ratio of radioactive carbon to ordinary carbon. Once something dies, the amount of C-14 begins to decrease. The ratio of C-14 to C-12 can be used to determine its age. Radioactive uranium is used to date nonorganic material such as rocks.
Examples of half Life 1. How much of a 10.0 g sample of I131 is left after 48 days? (1/2 life = 8 days) 2. After how many days will a 24 g sample decay to 3.0 g? 3. After 95 days, a 24 g sample of radioactive material decays, leaving 0.75g. What is the half-life of this material? Periodic Law (Periodicity) Properties repeat at regular
intervals when elements are arranged according to increasing atomic number Group/family = column; Period = row * Halogens Alkali Metals Alkaline Earth Metals Transition Metals Inner Transition Metals Noble Gases Metal/Metalloid/
7A 6A . Atomic Number = # of protons INC Atomic Mass = # of protons & neutrons INC Nuclear pull = electrostatic attraction of + nucleus for the
negative outer eINC Shielding = e- in between nucleus & outer e- shield pull Constant INC Atomic Radius Atomic Radius = the distance between the nucleus and the outermost electrons. INC e- are added to successively higher
energy levels. We remain in the same principle energy level. Each element has one p+ and one e- more than the preceding element. The nuclear pull increases pulling each new e- closer to the nucleus. The atomic radii of these representative elements are given in nanometers (nm). H 0.030 Increasing atomic radii Li 0.123 Be
0.089 Na 0.157 Mg 0.136 B 0.080 C 0.077 N 0.070 Al 0.125
Si 0.117 P 0.110 S 0.104 Cl 0.099 Ge 0.122 As 0.121 Se 0.117
Br 0.114 Sb 0.140 Te 0.137 I 0.133 K 0.203 Ca 0.174 Ga
0.125 Rb 0.216 Sr 0.191 In 0.150 Increasing atomic radii Sn 0.140 O 0.066 F
0.064 Ionic Radius (Size) Size or radius of an ion INC Cations Anions The overall trend is the same as Atomic size for the same reasons, however: Cations have lost e- so they are smaller Anions have gained e- so they are larger The ionic radii shown here are given in nanometers. Li+
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