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Unit 3 I,II,III(excluding Nuclear Chemistry) Test I. Internal Atomic Structure A. Discovery of Elementary Particles pages 39-54 Atomic Theory • 400 BC - Democritus – “atomos” – 4 elements earth, air, fire, and water • Alchemy – atoms of one element can change to another element • Robert Boyle – element is when can longer break down substances • Lavoisier – law of conservation of mass – mass is neither created nor destroyed • Proust – law of definite proportion – a given compound always contains exactly the same proportion(%) of elements by mass • Dalton’s Atomic Theory – be familiar with basic premises • Some of these basic ideas were: (some are not true today) 1) All matter is made of very small, discrete particles called atoms. (No internal structure, just solid matter) 2) All atoms of an element are alike in weight, and this weight is different from that of any other kind of atom. Not true today – isotopes: have different numbers of neutrons 3) Atoms cannot be subdivided, created, or destroyed. Not true today – can split atoms, they are not indivisible 4) Atoms of different elements combine in simple whole- number ratios to form chemical compounds 5) In chemical reactions, atoms are combined, separated or rearranged. (bonds broken and formed) • Dalton used his model to predict how a given pair of elements might combine to form more than one compound. Since he correctly predicted the formation of multiple compounds between two elements, his atomic theory became widely accepted. • By the second half of the 1800s, many scientists believed that all • Half-life- time required for half of the atoms of a radioactive nuclide to decay. • 5 kinds of emissions (radioactivity) 1. Alpha particles – α (Helium Nuclei) Thomson (Plum pudding model)– discovery of electron with cathode ray tube(meant also positive particles in atom to give 4 neutral He charge), found charge to mass ratio for electron (is greater 2 than proton) • Henri Becquerel – found that a piece of a mineral containing uranium could produce its image on a photographic plate without light. He found the source of this to be radioactivity – the Honors Chemistry -Outline NuclearbyChemistry emission of radiation uranium inTest this case. Found • Tospontaneous specify which of+the isotopes of an element we Atoms The Building Blocks of Matter that atoms 4 radiation. 234 spontaneously emit talking about, we use–the symbol:charge of electron. Using • are Millikan oil drop experiment determined 2 90 Half-liferequired half ofThomson, the atoms a radioactive the time charge to mass ratio from heof found the mass of the A for -31 (9.11 xZ10 kg) nuclideelectron to decay. Radioactive particles 5 kinds ofo emissions (radioactivity) • Ex. 238 92 • U Th He X •• Where • Cannot penetrate paper, skin (not large, so 1. Alpha particles – α (Helium Nuclei) o X = the symbol thefar) element doesn’t goof very o A= the mass number (number of protons and 4• Very He dangerous if ingested neutrons) 2 o Z = the atomic number (number of protons) 0 protons + number of neutrons 2. Beta Particlesβ or of Ex. • Mass number = number an electron or A = Z + # of neutrons, -1 so A – Z = #- just of neutrons Ex. Carbon-14 (t about life) Radiationγ+–5270 Highyears=half 238 3. Gamma 4energy photons w/ no mass 234 1/2 + Ex. 14 14 02 average of the atomic 92 90 mass – the weighed • Average atomic of7226 + -1 + element. • masses Rutherford’s gold foiloccurring experiment (The of nuclear atom)0 6239 the naturally an 4isotopes e 90 1 0 U He Th C N e γ but a Raparticles Cc. averageo isotopic He [4.1b] Shot alpha radium. Most went through, (atomic) mass;from calculations 0 88 2 few bounced which showed Thomson’s • The atomic mass can be calculated by that multiplying •Average + back, Cannot penetrate paper, skin (not large, so the model 1 0 was incorrect as there is e arelative small, abundance densely packed positively mass ofp each isotope by its n atomic doesn’t go very far) •(expressed Very dangerous charged center(nucleus). Predicted existence of neutrally 1 in decimal -1 form) and adding the results. • • Passes through wood, skin, humanforbody •of one Very dangerous ingested charged particle inifpaper, nucleus to account missing mass. Size carbon atom = 12 amu • Stopped by lead or several meters of concrete •*What Chadwick – discovered happens in betaneutron emission Positron –paper, mass ofskin electron, oppositely charge, • Can4. penetrate 0 considered anti-matter Beta Particlesβ orpiece • Can2.be stopped by thin of foil or wood -1 Ex. Carbon-11 e Ex. Carbon-14 (t1/2 about 5270 years=half life) 11 14 66 11 10 C C 11 14 57 pn 11 01 BN ++ 00 1-1 ee np ++ 00 1-1 ee Proton became neutron plus positron *What happens 5. Electron capture in beta emission • Can penetrate paper, skin • Can be stopped by thin piece + of foil or wood o + or – Atomic structure + - attract ++ and -- repel • electron “e-“ is what moves to create electricity Photoelectric Effect – for moreofsee • To specify which thepacket isotopes of an element we • An experiment which provides compelling proof for the photon are talking about, we use the symbol: nature of light (also called the particle nature of light) is the photoelectric effect.AIn this effect light is shone at a metal plate, and it is found Z that electrons are ejected. These electrons then get accelerated to a nearby plate by an external potential • Where difference, and a photoelectric current is established, as below. o X = the symbol of the element • The explanation, which was first given by Einstein and which o Ahim = the theNobel massPrize, number (number of photon protons won is as follows. Each hitsand an electron in the metal, giving up its energy to the electron. This neutrons) can sometimes be enough energy to free the from the o Z = the atomic number (number ofelectron protons) attractive forces holding it in the metal. The electron is then • Mass number number of protons + number neutrons accelerated (or = moves quickly) towards the other side,ofcausing oraAflow = Zof+charges # of neutrons, A – Z This = # effect, of neutrons and hence so a current. which arises in devices such as burglar alarms, cannot be explained using a “wave” picture of light. For example, it is found experimentally II. Externalthat Structure the photoelectric current depends the atomic •Atomic Average atomic mass – the weighedcritically average on of the massesofofthe thelight naturally of an element. frequency beingoccurring used. If isotopes the frequency of the light A. Spectroscopy pages 275-285; 3: c. average mass; calculations [4.1b] used is tooisotopic low, then(atomic) no current is observed. Red light isappendix the A16-A19 lowest • Thefrequency Average atomic mass canisbe calculated by multiplying light and violent the highest frequency light the atomic mass ofEinstein each isotope by its relative abundance • Photoelectric effectsaid light must be quantized in the visible spectrum. (expressed in decimal form) and adding the • Important conclusions from the work of Einstein results. and Planck: • Size one carbon atom = 12It amu 1. ofEnergy is quantized. can occur in only discrete amounts of quantum. (quantum mechanics) 2. Light has characteristics of both waves and particles (called photons). The phenomenon is sometimes referred to as the dual nature of light. X • • • • • Einstein used monochromatic light A minimum frequency is required in order to produce a current o Current = flow of electrons Einstein – light travels in bundles/packets of energy called photon Energy=constant time frequency of light Einstein single handedly advanced science 50 years at the time Flame Test (Lab) • Electrons in ground state are at the lowest energy state • Excited state • When come down to ground state, unique color is produced • On test: If gave ROYGBIV – Where is the longest wave length? – Red, Shortest - Violet B.b.The Bohr Atom 285-290 Faraday and electrolysis C.the Wave of Electrons 290-299 In early Nature 1830s, Michael Faraday discovered that water solutions of certain substances conduct an electric current. He called299-314 these D. Atomic Properties & Atomic Structure substances electrolytes. Our definition today an “Review electrolyte is much 1” p. of 319 Question the same. It is a substance that dissolves in water to form a solution that #31,33,35,37,41,45,47,49,67,68,71,73,75,78,80,83,85,87,93,99,101,117,118,12 will conduct an electric current. The usual apparatus to test for this 2,123,135 conductivity is a light bulb placed in a series of twop.prongs that are19, 20, 25 990 #13-15; in the solution tested, as shown below. Solutions can be good, III. immersed Periodic Properties moderate or poor electrolytes. Nonelectrolytes do not conduct at all. A. Periodic Law pages 299-309 B. Periodic Properties of Elements 314-318; chapters 19-21 2. Electrons: Thompson and Millikan – see above and below for more Thomson