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Atoms, Atoms Molecules, Molecules and Ions Chemistry Timeline #1 B.C. 400 B.C. Demokritos and Leucippos use the term "atomos” 2000 years of Alchemy 1500's Georg Bauer: systematic metallurgy Paracelsus: medicinal application of minerals 1600's Robert Boyle:The Skeptical Chemist. Quantitative experimentation, identification of elements 1700s' Georg Stahl: Phlogiston Theory Joseph Priestly: Discovery of oxygen Antoine A t i L Lavoisier: i i Th The role l off oxygen iin combustion, b ti llaw off conservation ti off mass, first modern chemistry textbook Chemistry Timeline #2 1800's Joseph Proust: The law of definite proportion (composition) John Dalton: The Atomic Theory, The law of multiple proportions Joseph Gay-Lussac: Combining volumes of gases, existence of diatomic molecules Amadeo Avogadro: Molar volumes of gases Jons Jakob Berzelius: Relative atomic masses, modern symbols for the elements Dmitri Mendeleyev: The periodic table J.J. Thomson: discovery of the electron Henri Becquerel: Discovery of radioactivity 1900's 1900 s Robert Millikan: Charge and mass of the electron Ernest Rutherford: Existence of the nucleus, and its relative size Meitner & Fermi: Sustained nuclear fission Ernest Lawrence: The cyclotron and trans-uranium elements Dalton’s Atomic Theory (1808) All matter is composed of extremely small particles called atoms Atoms of a given element are identical in size, mass, and other properties; atoms of different John Dalton elements l differ diff in i size, i mass, and d other properties Atoms cannot be subdivided, created, or destroyed Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions reactions, atoms are combined, combined separated, or rearranged Modern Atomic Theory Several changes have been made to Dalton’s theory. Dalton said: Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, size mass mass, and other properties Modern theory states states: Atoms of an element have a characteristic average mass which is unique to that element. l Modern Atomic Theory y #2 Dalton said: Atoms cannot be subdivided, created, or destroyed Modern theory states: Atoms cannot be subdivided, created, or destroyed in ordinary y chemical m reactions.. However,, these changes CAN occur in nuclear reactions! Discovery of the Electron In 1897, 1897 J.J. J J Thomson used a cathode ray tube to deduce the presence of a negatively charged particle. Cathode ray tubes pass electricity through a gas that is contained at a very y low pressure. p Thomson’s Atomic Model Thomson h believed b l d that h the h electrons l were like l k plums l embedded in a positively charged “pudding,” thus it was called the “plum p pudding” p g model. Mass of the Electron 1909 – Robert Millikan determines the mass of the electron. The oil drop apparatus Mass of the electron is 9.109 x 10-31 kg Conclusions from the Study of th El the Electron t Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons. Atoms are neutral, neutral so there must be positive particles in the atom to balance the negative charge of the electrons Electrons have so little mass that atoms must contain other particles that account for most of the mass Rutherford’s Gold Foil Experiment Alpha particles are helium nuclei Particles were fired at a thin sheet of gold foil Particle P ti l hit hits on th the d detecting t ti screen (fil (film)) are recorded Try it Yourself! In th I the f following ll i pictures, i t th there iis a ttargett hidd hidden b by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target? The Answers Target #1 Target #2 Rutherford’s Findings M Mostt of f the th particles ti l passed d right i ht through th h A few particles were deflected VERY FEW were greatly g y deflected “Like howitzer shells bouncing off of tissue paper! paper!” Conclusions: The nucleus is small The nucleus is dense The nucleus is positively charged Atomic Particles Particle Charge El t Electron -1 1 31 9 109 x 10-31 9.109 Electron El t cloud Proton +1 1.673 x 10-27 Nucleus 0 1.675 x 10-27 Nucleus Neutron Mass (kg) Location The Atomic Scale Most of the mass of the atom is in the nucleus (protons and neutrons) Electrons are found outside of the nucleus (the electron l t cloud) l d) Most of the volume of the atom is empty p y space p “q” q is a particle called a “quark” quark About Quarks… Protons and neutrons are NOT fundamental particles. Protons are made of two “up” quarks and one “down” down quark. quark Neutrons are made of one “up” up quark and two “down” quarks. Quarks are held together by “gluons” Isotopes Isotopes I t are atoms t of f the th same element l t having h i different masses due to varying numbers of neutrons. Isotope Protons Electrons Neutrons Hydrogen–1 (protium) 1 1 0 Hydrogen-2 (d t i ) (deuterium) 1 1 1 Hydrogen-3 y g (tritium) 1 1 2 Nucleus Atomic Masses Atomic mass is the average g of all the naturally y isotopes of that element. Carbon = 12.011 Isotope Symbol Composition of the nucleus % in nature Carbon-12 12C 6 protons 6 neutrons 98.89% Carbon-13 13C 6 protons 7 neutrons 1.11% Carbon-14 14C 6 p protons 8 neutrons <0.01% Atomic Number Atomic number (Z) of an element is the number of protons in the nucleus of each atom of f th thatt element. l t Element # of protons Atomic # (Z) 6 6 Phosphorus 15 15 Gold 79 79 Carbon Mass Number Mass number is the number of protons and neutrons in the nucleus of an isotope. Mass # = p+ + n0 Nuclide p+ n0 e- 8 10 8 18 Arsenic - 75 33 42 33 75 - 31 Ph Phosphorus h 15 16 15 31 1 Oxygen - 18 Mass # Molecules Two or more atoms of the same or different elements, covalently bonded together. Molecules are discrete structures, and their formulas represent each atom present in the molecule. Benzene,, C6H6 Covalent Network Substances Covalent network substances have covalently bonded atoms, but do not have discrete formulas. Why Not?? Graphite Diamond Ions Cation Cation:: A positive ion • Mg2+, NH4+ Anion Anion:: A negative ion Cl, SO42 Ionic Bonding: Bonding: Force of attraction between oppositely charged ions. Ionic compounds form crystals, so their formulas are written empirically (lowest whole number ratio of ions). Periodic Table with Group Names The Properties of a Group: the Alkali Metals Easily lose valence electron (Reducing agents) Reactt violently R i l tl with ith water t Large hydration energy React with halogens to form salts Predicting Ionic Charges Group 1: 1: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+ Predicting Ionic Charges Group 2: 2: Loses 2 electrons to form 2+ ions Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Predicting Ionic Charges B3+ Al3+ Ga3+ Group G 13: Loses 13: L 3 electrons to form 3+ ions Predicting Ionic Charges Caution! C22- and C4are both called carbide Group G 14: Loses 14: L 4 electrons or gains 4 electrons Predicting Ionic Charges N3- Nitride P3- Phosphide As3- Arsenide Group G 15: Gains 15: G i 3 electrons to form 3- ions Predicting Ionic Charges O2- Oxide S2- Sulfide Se2- Selenide G i 2 Group G 16: Gains 16: electrons to form 2- ions Predicting Ionic Charges F1- Fluoride Br1- Bromide Cl1-Chloride I1- Iodide Group G 17: Gains 17: G i 1 electron to form 1- ions Predicting Ionic Charges Group G 18: Stable 18: St bl Noble gases do not form ions! Predicting Ionic Charges Groups 3 - 12 12:: Many transition elements have more than one possible oxidation state. Iron(II) = Fe2+ Iron(III) = Fe3+ Predicting Ionic Charges Groups 3 - 12 12:: Some transition elements have only one possible oxidation state. Zinc = Zn2+ Silver = Ag+ Writing Ionic Compound Formulas Example: Barium nitrate 1. Write the f formulas f for the cation and anion, including CHARGES! 2.. Check to see if f charges g are balanced. 2+ ( Ba NO3 ) 2 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. ion Not balanced! Writing Ionic Compound Formulas Example: Ammonium sulfate 1. Write the f formulas f for the cation and anion, including CHARGES! 2.. Check to see if f charges g are balanced. ( NH4+) SO42- 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. ion 2 Not balanced! Writing Ionic Compound Formulas Example: Iron(III) chloride 1. Write the f formulas f for the cation and anion, including CHARGES! 2.. Check to see if f charges g are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. ion Fe33+ Cl- 3 Not balanced! Writing Ionic Compound Formulas Example: Aluminum sulfide 1. Write the f formulas f for the cation and anion, including CHARGES! 2.. Check to see if f charges g are balanced. 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. ion 3+ Al 2 2 S 3 Not balanced! Writing Ionic Compound Formulas Example: Magnesium carbonate 1. Write the f formulas f for the cation and anion, including CHARGES! 2.. Check to see if f charges g are balanced. Mg22+ CO32They h are balanced! b l d! Writing Ionic Compound Formulas Example: Zinc hydroxide 1. Write the f formulas f for the cation and anion, including CHARGES! 2.. Check to see if f charges g are balanced. 2+ Zn 3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. ion ( OH- )2 Not balanced! Writing Ionic Compound Formulas Example: Aluminum phosphate 1. Write the f formulas f for the cation and anion, including CHARGES! 2.. Check to see if f charges g are balanced. 3+ Al 3 PO4 They ARE balanced! Naming Ionic Compounds • 1. Cation first, then anion • 2. 2 Monatomic cation = name of the element • Ca2+ = calcium ion • 3. Monatomic anion = root + -ide chloride • Cl = chloride • CaCl2 = calcium chloride chloride Naming g Ionic Compounds p (continued) Metals with multiple p oxidation states some metal forms more than one cation use Roman numeral in name PbCl2 Pb2+ is the lead(II lead(II)) cation PbCl2 = lead(II lead(II)) chloride Naming g Binary y Compounds p Compounds between two nonmetals First element in the formula is named first. first. Second element is named as if it were an anion anion.. Use prefixes Only use mono on second element P2O5 CO2 CO N2O = di diphosphorus phosphorus p p pentoxide pent p oxide = carbon di dioxide oxide = carbon mon monoxide oxide = di dinitrogen nitrogen mon monoxide oxide