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MR. CANOVA’S Science, Technology, & Society CLASS CHEMISTRY REVIEW: HISTORY OF THE ATOMIC MODEL SUBATOMIC PARTICLES IONIC AND MOLECULAR COMPOUNDS NAMING AND WRITING FORMULAS ACIDS HISTORY OF THE ATOMIC MODEL SCIENTIST Democritus: MODEL The Greek Model (460 BC-370 BC) •Matter can’t be divided forever; there must be a smallest piece (atomos) •Atoms are indestructible, indivisible, & the fundamental units of matter Atom: smallest particle of an element that retains the properties of that element. - no electric charge, electrically neutral •No experiments to test his theories SCIENTIST MODEL John Dalton: Dalton’s Model (1766-1844) Dalton’s Atomic Theory: All elements are composed of atoms that are submicroscopic indivisible particles. Atoms of the same elements are identical & atoms of different elements are different. Atoms of different elements can physically mix together or chemically combine w/one another to form simple or wholenumber ratios to form compounds. Chemical reactions occur when atoms are separated, rearranged or joined. Atoms of one element can never be changed into atoms of another element. SCIENTIST MODEL J.J. Thomson: Thomson’s Model (1856-1940) • Used cathode ray tube to discover electrons • Cathode ray: glowing beam which travels from the cathode(-) to the anode(+). - are composed of electrons - are attracted to positive metal plate • Atoms had negatively charged particles • ELECTRON: negatively charged subatomic particle • “Plum Pudding” Model • (chocolate chip cookie) (watermelon with seeds) -a ball of positive charge containing electrons Thomson’s Model POSITIVE CHARGE ELECTRONS EMBEDDED WITHIN Cathode Ray Tube: Robert Millikan Oil Drop Experiment (1916) Determined the charge and mass of an electron The mass is 1/1840 of the mass of a hydrogen atom (less than 1 amu) SCIENTIST E. Rutherford: +++ +++ • • MODEL Rutherford’s Model Empty Space + Nucleus Gold Foil Experiment Discovered that most of atom’s mass is located in the positively charged nucleus NUCLEUS: center of the atom composed of PROTONS & NEUTRONS is 99.9% of the atom’s mass a marble in a football stadium www.shsu.edu/%Echm_tgc/sounds/ruther.mov Gold Foil Experiment: Rutherford PROTON: positively charged subatomic particle discovered by Eugen Goldstein (1850-1930) put holes in cathode and saw rays traveling in the opposite direction (canal rays) NEUTRON: subatomic particle with no charge discovered by Sir James Chadwick (1891-1974) mass is nearly equal to proton (1 amu) Thomson & Rutherford proved Dalton’s Theory incorrect: ATOMS ARE DIVISIBLE http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf SCIENTIST Niels Bohr: MODEL The Bohr Model (1885-1962) Electrons +++ +++ Energy Levels Electrons move in definite orbits around the nucleus (planets around the sun) PLANETARY MODEL Electrons are a part of energy levels located certain distances from the nucleus Energy Levels: region around the nucleus where the electron is likely to be moving. a ladder that isn’t equally spaced further the distance, closer the spacing the higher the energy level the farther it is from the nucleus Electrons can jump from 1 energy level to another. Quantum Energy: amount required to move an electron from its present energy level to the next higher one. SCIENTIST Erwin Schrodinger • • • • MODEL Quantum Mechanic Model (1887-1961) Wave mechanics-mathematical Probable location of electron Cloud Shaped Propeller blade Subatomic particles: Electrons, Protons, & Neutrons Atomic Number: Number of Protons in the nucleus Whole number written above chemical symbol Ex: Hydrogen=1(P) Oxygen=8(P) SUBATOMIC PARTICLES Subatomic particles: Electrons, Protons, & Neutrons Atomic • Number: Number of Protons in the nucleus Whole number written above chemical symbol Ex: Hydrogen=1(P) Oxygen=8(P) Mass Number: Sum of Protons + Neutrons Ex: Carbon Mass #12 = 6(P) + 6(N) Oxygen Mass #16 = 8(P) + 8(N) Mass # (#P + #N) - Atomic # (#P) = #Neutrons LETS HAVE SOME PRACTICE Element Symbol Element Name Mass Number (P+N) Atomic Number (P) Atomic Number (P) 6 C Carbon 12 12 6 Mass Number (P+N) C WHAT GIVES AN ATOM ITS IDENTITY? Isotope: Same # of Protons, different # of Neutrons • Different Mass Number • Same Atomic Number • Chemically alike Ex: Carbon-12 Mass #12 = 6(P) + 6(N) Carbon-13 Mass #13 = 6(P) + 7(N) Atomic Mass for isotopes of Carbon = 12.01 amu SO, WHAT GIVES AN ATOM ITS IDENTITY? # of protons gives the atom its identity # of electrons determines the chemistry of the atom # of neutrons only changes the mass of the atom HOW TO DETERMINE ELECTRON CONFIGURATIONS How electrons are arranged around the nuclei of atoms 3 RULES: Aufbau’s • Electrons enter lowest energy level first Pauli Exclusion Principle • Orbitals can hold 2 electrons of opposite spin Hund’s • Electrons enter one orbital until parallel spins Orbitals and Electron Capacity of the First Four Principle Energy Levels Principle energy level (n) 1 Type of sublevel # of orbitals per type s s p 1 1 3 3 s p d 4 s p d f 2 # of orbitals per level (n2) Maximum # of electrons (2n2) 1 2 4 8 1 3 5 9 18 1 3 5 7 16 32 USING THE PERIODIC TABLE Column # NAME Valence electrons Ion Charge 1 Alkali Metals Lose 1 +1 2 Alkaline Metals Lose 2 +2 3 to 12 Transition Metals Lose VARIES 13 Boron group Lose 3 +3 14 Carbon group Lose/Gain 4 +/- 4 15 Nitrogen Group Gain 3 -3 16 Oxygen Group Gain 2 -2 17 Halogens Gain 1 -1 18 Inert or Noble Gases Stable 0 IONIC AND MOLECULAR COMPOUNDS MOLECULAR VS. IONIC COMPOUNDS MOLECULAR COMPOUNDS: 1. Low melting & boiling points 2. Solids, Liquids, and Gases at room temp. 3. Sharing of valence electrons 4. Two or more Nonmetallic elements 5. Contain covalent bonds EX: H2 O CO2 CH4 MOLECULAR VS. IONIC COMPOUNDS IONIC COMPOUNDS: 1. High melting & boiling points 2. Composed of ions (cation and anion) 3. Electrically neutral 4. Crystalline solids at room temperature -coordination #, 3D patterns 5. Composed of a Metal and Nonmetal 6. Contains Electrostatic Bonds EX: NaCl MgCl2 How to Write an Ionic Formula: 1. Write down symbols 2. Determine Ionic Charges 3. Charges must cancel each other out (equal zero) if not, use criss-cross method to form subscripts to cancel out charges EXAMPLES: Potassium Bromide K+1 Br-1 charges cancel KBr Magnesium Oxide Mg+2 O-2 charges cancel MgO Aluminum Nitride Al+3 N-3 charges cancel AlN Magnesium Chloride Mg+2 Cl-1 charges don’t cancel, criss-cross MgCl2 Sodium Sulfide Na+1 S-2 Na2S charges don’t cancel, criss-cross Aluminum Oxide Al+3 O-2 charges don’t cancel, criss-cross Al2O3 Naming an Ionic Formula: 1. Write the name for the metal and nonmetal 2. Check to see if the metal has more than one charge (Cu, Fe, transition metals) 3. If metal has more than one charge, you must do a “reverse” criss-cross to determine formula A Roman Numeral goes between the two names 4. Change the nonmetal ending to IDE EXAMPLES: KBr potassium bromide Na2O sodium oxide MgS magnesium sulfide Cu As2 Fe2 Br2 O5 O3 copper II bromide arsenic V oxide iron III oxide How to Name a Molecular Formula: Ex: CO CO2 1. Element with the (+) apparent charge comes 1st carbon carbon 2. Second element ends in IDE carbon oxide carbon oxide 3. Use prefixes to distinguish between compounds & to show how many atoms of each element are present carbon monoxide carbon dioxide Prefixes for Molecular Compounds: 1. drop vowel on prefix if element starts with vowel EX: monooxide = monoxide 2. Don’t drop vowel for di and tri prefixes 1 mono Don’t use for first named element 2 3 4 5 6 7 8 9 10 di Ex: CO tri carbon monoxide tetra penta hexa hepta octa nona deca EXAMPLES: NO nitrogen monoxide NO2 nitrogen dioxide N2O dinitrogen monoxide N2O3 dinitrogen trioxide PCl5 phosphorus pentachloride CS2 carbon disulfide SF6 sulfur hexafluoride How to Write a Molecular Formula: 1. Write down element symbol 2. Prefixes give you what subscripts to use EXAMPLES: nitrogen monoxide NO nitrogen dioxide NO2 dinitrogen monoxide N2O dinitrogen trioxide N2O3 phosphorus pentachloride PCl5 carbon disulfide CS2 sulfur hexafluoride SF6 REMINDER WHEN WRITING FORMULAS: CHECK YOUR HOLY SHEETS FOR ANY POLYATOMIC IONS TREAT THEM AS EITHER A CATION OR AN ANION An ACID is a substance that when put into water, gives away a hydrogen ion (H+1) to another substance in the water solution. HCl + H2O HCl(aq) There are two types of acids: 1. Binary acids-HCl(aq) 2. Ternary acids-H2SO4(aq) -polyatomic ions (ending in ate) -polyatomic ions (ending in ite)