Unit 2 Notes: Atomic Theory Chem

Early models of the atom Aristotle- thought everything was made of earth, fire, water & air Democritus- matter made up of tiny indivisible particles called atoms Atom- smallest part of an element that retains the properties of that element

Dalton’s Atomic Theory 1) All elements composed of tiny indivisible particles called atoms. 2) Atoms of same elements are identical; atoms of 1 element are different from atoms of another element 3) Atoms can mix together in simple whole number ratios. 4) Chemical reactions are when atoms are separated, joined or rearranged but atoms can’t change into atoms of another element as a result of a chemical reaction.

Law of Definite Proportions: a compound is always composed of the same elements in the same proportion by mass Percent by mass = mass of element x 100 mass of compound Law of Multiple Proportions: when different compounds are formed by the combination of the same elements, different masses of one element combine with the same relative mass of the other element in a ratio of small whole numbers How does the atomic theory account for these laws?

Structure of Atom: Electron- neg., charged subatomic particle- Discovered by J.J. Thomson using cathode ray tube Cathode ray attracted to + chg, repelled by – chg - Millikan oil drop experiment determines chg (-1) and mass (1/1840 mass of H atom) 5.486X amu Electron has particle wave duality (Properties of both a wave and a particles) Found to be in electron cloud around nucleus

Proton- positively charged subatomic particle Goldstein found 1840 X e- mass; amu Neutron- neutral charged subatomic particle - Discovered by Chadwick mass ~ to proton; amu ParticleChargeLocation Mass

Nucleus- - Discovered by Rutherford’s Gold Foil Experiment - Shot alpha particles (from radioactive lead) through gold foil - He expected it to go through - Some bounced back - Decided it had a dense center called it nucleus - Nucleus is most dense has most mass, has protons & neutrons - Decided electrons around nucleus

Models of Atom J.J. Thomson- Plum Pudding Model Rutherford- “nuclear atom” e- orbit around nucleus Bohr- e- in orbits around nucleus like the planets around sun “planetary model” Quantum Mechanical Model- e- are in specific orbitals around nucleus

Atomic Number- # protons in nucleus Atoms are electrically neutral so #p = #e; Z Mass Number (A)= #p+ #n Mass # - #p = #n Shorthand: Mass number Symbol Protons

Isotopes Isotope- same # p, different # n; so different mass Nuclide-nucleus of specific isotope Three ways to represent an isotope: hydrogen-1; H-1; 1 H 1

Carbon has 4 isotopes, with mass numbers 11, 12, 13 & 14. Write the complete chemical symbols for each of them. Give the chemical symbol for the nuclide that contains 18 protons, 18 electrons & 22 neutrons.

Problems: Fill in the chart: ElementMass # Atomic # Protons # Electrons # Neutrons Be Na

Amu- (atomic mass unit) 1/12 C-12 atom Average atomic mass- what is on PT -Based on natural abundance Change % to decimal Multiply decimal by the mass Add the numbers together Element X has two isotopes. The isotope with a mass of amu has a relative abundance of 19.91%. The isotope with a mass of amu has a relative abundance of 80.09%. Calculate the atomic mass of this element.

Fundamental Particles & Interactions

Intro to quarks 12 Particles make up matter Quarks + electrons = atoms

Lepton May be found by themselves Ex: electron, muon, tau: same charge as electron (-) but more massive Ex: 3 Neutrinos (no electric charge, no mass) For each lepton there is an anti- lepton with equal mass and opposite charge Ex: electron & positron

Quarks 1960’s used particle accelerator to find: Gell-Mann & Zweig found quarks There are quarks & Anti-quarks: have same masses but opposite charges Quark+ anti-quark= annihilate; disappearing to give another form of energy There are 6 types of quarks (up, down, strange, charm, bottom & top in order of increasing mass) Only in hadrons (composite particles) 2 classes: baryons (contain 3 quarks) Mesons (contain 1 quark & 1 anti quark)

Quarks LighterHeavier -1/3 +2/3 DownUp StrangeCharm BottomTop Protons= 2 up +1 down Neutron= 2 down + 1 up

Forces holding atoms together 4 types of interactions: gravitational, electromagnetic (hold electrons to protons), strong (hold quarks together to form glucons; allows for protons and neutrons to hold together in nucleus) & weak (only processes allowing quarks to change to other quarks or leptons to change to other leptons; also allow for decay of massive quarks & leptons to produce lighter quarks)

Nucleon- two subatomic particles in nucleus Radionuclides- radioactive nuclei Radioisotopes- atoms w/radionuclides

Nuclear Chemistry Radioactive decay: atoms w/ “wrong” p:n give off radiation to gain stability TypeSymbolPowerShielding alpha 4  4 He 2 lowPaper & clothing beta 0  0 e mediumMetal foil gamma 0 00 0 highLead & concrete

U-238 undergoes alpha decay. Write the nuclear equation. U-238 undergoes beta decay. Write the nuclear equation. U-238 undergoes gamma & beta decay. Write the nuclear equation.

Other types of radioactive decay Positron- same mass as electron but positively charged 0 e; 1 Carbon-11 decays using positron emission. *effect of converting proton to a neutron=decrease atomic # by 1

Other types of radioactive decay Electron capture- nucleus captures an electron from the electron cloud Electron consumed shown on reactant side of reaction Converts a proton to a neutron 81 Rb + 0 e  81 Kr

Half-life- time for ½ of the nuclei to decay to products Used for radioactive dating Medical procedures (diagnose & treat disease), trace particle through system (DNA, fertilizers) 2.00 g of N-13 emits B radiation & decays to O-13 with a ½ life of 10 minutes. How long is 3 half-lives? How many g of the isotope are left after 3 half lives?

Transmutation- conversion of 1 atom to another Transuranium elements- atomic number above 92 are man made Radioactive series Fission- splitting nucleus into smaller fragments by bombarding it with neutrons Chain reaction, high energy, use control rods to slow reaction Uses: bombs, nuclear power Fusion:nuclei combine to produce a nucleus of greater mass Lots of E, process too hot to control, sun