Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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: The grass on the playground is wet. Possible inferences: It rained. The sprinkler was on. There is morning dew on the grass. 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 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 that’s 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) 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. Solid Sphere Model. Nothing smaller = no subatomic particles 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 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 Gold Foil experiment When Rutherford directed a beam of positive α 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 Rutherford’s Experiment Back to Rutherford Rutherford’s experiment Back to Rutherford • 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. James Chadwick (1932) discovered a particle with no charge and a mass equal to a proton-he called it a neutron. 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 e- e- ee- ee- e- e- ee- •Nucleus (p+ & n0) •Concentric Circular orbits Cloud Model 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 don’t electron’s 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+ & nº (e- have no mass) Complete Shorthand Symbol “top heavy” atomic Mass 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 nº and atomic masses Sym-mass 13C U-235 H-3 C-14 6 The number is the atomic mass Formulas: # of p+ = Atomic Number # of nº = Atomic Mass – Atomic Number # of e- = Atomic Number – charge Examples: 35 Cl –1 17 Mg+2 19 F –1 9 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 = Σ [abundance * mass] (sum of) EX: 63 Cu 29 69.1 % 65 Cu 29 30.9 % (63 * 0.691) = (65 * 0.309) = 63.618 Try These Problem #3: Chlorine Problem #4: Silicon mass number exact weight percent abundanc e mass number exact weight percent abundanc e 35 34.968852 75.77 28 27.976927 92.23 37 36.965903 24.23 29 28.976495 4.67 30 29.973770 3.10 The answer for chlorine: 35.453 The answer for silicon: 28.086 Warm up 9-15-14 1. For Ca2+ find the: Electrons Protons Neutrons Atomic Mass Atomic Number 2. Find the Average mass for Silver: Isotope name Isotope mass (a mu) percentage Silver-107 106.90509 51.86 Silver-109 108.90470 remainder Radioactive Isotopes (radioactive…radioactive) Some 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 (α) Beta particles (β- & β+) Gamma ray (γ) 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 Particle a 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 Particle b Characteristics Range • -1 charge • Short range • Plastic safety glasses • About 10' in air • Thin metal • Small mass Shielding Hazards Sources • Skin and eyes •Radioisotopes • Can be internal • Activation Products • Sealed sources Gamma Ray g Characteristics Range Shielding • No charge • No mass • Similar to x-rays • Lead • External • 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 Particle h Characteristics Range Shielding Hazards Sources • No charge • Found in nucleus • Water • Plastic • External (whole body) • Fission • Reactor operation • Sealed sources • Accelerators • Extended range Paper Lead Water Half Life Half Life = (t1/2) The amount of time it takes for ½ of the radioactive isotope to decay (no longer there- changed into something else. Multiply the mass by ½ for each ½ 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 non-organic material such as rocks. Examples of half Life 1. How much of a 10.0 g sample of I-131 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/Nonmetal Nonmetals Metals Metalloids Representative Elements (1,2,13 – 18) 1A 8A 2A 3A 5A 4A B’s 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 ecloser 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+ 0.060 Be2+ 0.031 Na+ 0.095 Mg2+ 0.065 K+ 0.133 Ca2+ 0.099 Rb+ 0.148 Cs+ 0.169 Sr2+ 0.113 Ba2+ 0.135 B3+ 0.020 Al3+ 0.050 Ga3+ 0.062 In3+ 0.081 Tl3+ 0.095 C4+ 0.015 Si4+ 0.041 Ge4+ 0.053 Sn4+ 0.071 Pb4+ 0.084 N30.171 O20.140 P30.212 S20.184 Cl0.181 As30.222 Se20.198 Br0.195 Sb30.245 Te20.221 I0.216 F0.136