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Atoms, Ions and Molecules Chapter 2 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 elements differ in size, mass, and other properties John Dalton Atoms cannot be subdivided, created, or destroyed Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged Atomic Theory of Matter All matter is made of tiny indivisible particles called atoms. This proposal has been verified experimentally. Single atoms of a variety of elements have been photographed with a scanning transmission electron microscope. Atomic Theory of Matter 2. Atoms of the same element are identical and atoms of a different element have different masses and chemical properties. However you will learn that atoms of the same element can have different masses. Atomic Theory of Matter Atoms of different elements combine in whole number ratios to form compounds One molecule of water always consists of two atoms of hydrogen and one atom of oxygen. Atomic Theory of Matter 4. Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed. Modern research has altered this proposal. Atoms are not indestructible and may lose their identity when split during nuclear reactions. However Dalton’s proposal remains true, for chemical reactions. Law of Multiple Proportions Atoms of two or more elements may combine in different ratios to produce more than one compound. Law of Constant Composition A compound always contains two or more elements combined in a definite proportion by mass. Law of Conservation of Mass The total mass of materials present after a chemical reaction is the same as the total mass before the reaction This is the basis for which postulate? Parts of an Atom J. J. Thomson - English physicist. 1897 Made a piece of equipment called a cathode ray tube. Determined the charge to mass ratio It is a vacuum tube - all the air has been pumped out. Thomson’s Experiment Voltage source + - Vacuum tube Metal Disks Thomson Experiment Voltage source + - Passing an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage source + By adding an electric field Thomson’s Experiment Voltage source + By adding an electric field he found that the moving pieces were negative What Did Thomson Demonstrate? Cathode rays: Travel in straight lines Are negatively charged Are deflected by electric and magnetic fields Thomson’s Model Found the electron Said the atom was like plum pudding A bunch of positive stuff, with the electrons able to be removed Robert Millikan American Scientist Goal: Determine the charge on the electron to determine its mass Millikan’s Experiment Atomizer Oil droplets + - Telescope Oil Millikan’s Experiment X-rays X-rays give some drops a charge. Millikan’s Experiment Some drops would hover From the mass of the drop and the charge on the plates, he calculated the mass of an electron Radioactivity Discovered by accident French scientist Henri Bequerel Studying pitchblende Discovered that it spontaneously emits high energy radiation Three types alpha- helium nucleus (+2 charge, large mass) beta- high speed electron gamma- high energy light (Uranium compound) 2.2 Rutherford’s Experiment Ernest Rutherford English physicist. (1910) Believed in the plum pudding model of the atom. Used uranium to produce alpha particles. Rutherford’s Experiment Aimed alpha particles at gold foil by drilling hole in lead block. Since the mass is evenly distributed in gold atoms alpha particles should go straight through. Used gold foil because it could be made atoms thin. Rutherford’s Experiment When the alpha particles hit a florescent screen, it glows. Rutherford’s Experiment Lead block Uranium Florescent Screen Gold Foil What he expected Why ?? The alpha particles would pass through without changing direction very much The negative charges were spread out evenly. Alone they were not enough to stop the alpha particles What he got How He Explained It Atom is mostly empty Small dense, positive piece at center Alpha particles are deflected by it if they get close enough How He Explained It + Density and the Atom Since most of the particles went through, it was mostly empty. Because the pieces turned so much, the positive pieces were heavy. Small volume, big mass, big density This small dense positive area is the nucleus Discovery of the Neutron 9 4 Be + 4 2 He 12 6 C + 1 0 n James Chadwick bombarded beryllium-9 with alpha particles, carbon-12 atoms were formed, and neutrons were emitted. Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 764 *Walter Boethe Modern View The atom is mostly empty space Two regions Nucleus- protons and neutrons Electron cloud- region where you might find an electron Structure of Atom There are two regions: The nucleus: with protons and neutrons Almost all the mass Electron cloud- Most of the volume of an atom The region where the electron can be found Size of Atom Atoms are small. Measured in picometers, 10-12 meters Hydrogen atom, 32 pm radius Size of Atom Nucleus tiny compared to atom IF the atom was the size of a stadium, the nucleus would be the size of a marble. Radius of the nucleus near 10-15m. Density near 1014 g/cm3 Subatomic Particles ATOM ATOM NUCLEUS NUCLEUS ELECTRONS ELECTRONS PROTONS PROTONS NEUTRONS NEUTRONS POSITIVE Positive CHARGE Charge NEUTRAL Neutral CHARGE Charge NEGATIVE CHARGE Negative Charge equal in a Most of the atom’s mass. neutral atom QUARKS Subatomic particles Name Symbol Relative Charge mass Actual mass (g) Electron e- -1 1/1840 9.11 x 10-28 Proton p+ +1 1 1.67 x 10-24 Neutron no 0 1 1.67 x 10-24 Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei Mass Number A ZX Atomic Number 1 1H 235 92 2 1H U Element Symbol (D) 238 92 3 1H U (T) Symbols Find the number of protons number of neutrons number of electrons Atomic number Mass Number 19 9 F Symbols Find the –number of protons –number of neutrons –number of electrons –Atomic number –Mass Number 80 35 Br Symbols if an element has an atomic number of 34 and a mass number of 78 what is the number of protons number of neutrons number of electrons Complete symbol Atomic Mass How heavy is an atom of oxygen? There are different kinds of oxygen atoms. More concerned with average atomic mass. Based on abundance of each element in nature. Don’t use grams because the numbers would be too small Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope has its own atomic mass we need the average from percent abundance. Calculating averages You have five rocks, four with a mass of 50 g, and one with a mass of 60 g. What is the average mass of the rocks? Total mass = 4 x 50 + 1 x 60 = 260 g Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 Calculating averages Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 5 Average mass = .8 x 50 + .2 x 60 80% of the rocks were 50 grams 20% of the rocks were 60 grams Average = % as decimal x mass + % as decimal x mass + % as decimal x mass + Atomic Mass Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu. Atomic Mass Magnesium has three isotopes. 78.99% magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of 24.9858 amu, and the rest magnesium 25 with a mass of 25.9826 amu. What is the atomic mass of magnesium? If not told otherwise, the mass of the isotope is the mass number in amu The Periodic Table Noble Gas Halogen Group Alkali Metal Alkali Earth Metal Period 2.4 Atoms and ions Atoms are electrically neutral. Same number of protons and electrons. Ions are atoms, or groups of atoms, with a charge. Atoms and Ions Different numbers of protons and electrons. Only electrons can move. Gain or lose electrons. Anion A negative ion. Has gained electrons. Non metals can gain electrons. Charge is written as a super script on the right. -1 F -2 O Has gained one electron Has gained two electrons Cations Positive ions. Formed by losing electrons. More protons than electrons. Metals form cations. +1 Has lost one electron K +2 Has lost two electrons Ca Two Types of Compounds Molecular compounds Made of molecules. Made by joining nonmetal atoms together into molecules. Two Types of Compounds Ionic Compounds Made of cations and anions. Metals and nonmetals. The electrons lost by the cation are gained by the anion. The cation and anions surround each other. Smallest piece is a FORMULA UNIT. Two Types of Compounds Smallest piece Types of elements State Melting Point Ionic Molecular Formula Unit Molecule Metal and Nonmetal Nonmetals solid Solid, liquid or gas High >300ºC Low <300ºC Chemical Formulas Shows the kind and number of atoms in the smallest piece of a substance. Molecular formula- number and kinds of atoms in a molecule. CO2 Charges on ions For most of the Group A elements, the Periodic Table can tell what kind of ion they will form from their location. Elements in the same group have similar properties. Including the charge when they are ions. +1 +2 +3 -3 -2 -1 Naming ions We will use the systematic way. Cation- if the charge is always the same (Group A) just write the name of the metal. Transition metals can have more than one type of charge. Indicate the charge with roman numerals in parenthesis. Name these Na+1 Ca+2 Al+3 Fe+3 Fe+2 Pb+2 Li+1 Write Formulas for these Potassium ion Magnesium ion Copper (II) ion Chromium (VI) ion Barium ion Mercury (II) ion Naming Anions Anions are always the same. Change the element ending to – ide F-1 Fluoride Name these Cl-1 N-3 Br-1 O-2 Write these Sulfide ion iodide ion phosphide ion Strontium ion Polyatomic ions Groups of atoms that stay together and have a charge. You must memorize these (table 2.5). Acetate C2H3O2-1 Nitrate NO3-1 Nitrite NO2-1 Hydroxide OH-1 Permanganate MnO4-1 Cyanide CN-1 Polyatomic ions Sulfate SO4-2 Sulfite SO3-2 Carbonate CO3-2 Chromate CrO4-2 Dichromate Cr2O7-2 Chlorate ClO3- Phosphate PO4-3 Phosphite PO3-3 Hydronium H3O + Perchlorate ClO4Ammonium NH4+1 Chlorite ClO2 - Polyatomic Ions Hypochlorite ClOHydrogen carbonate ion HCO3Dihydrogen phosphate ion H2PO4- Ions and Ionic Compounds Naming Binary Ionic Compounds Binary Compounds - 2 elements. Ionic - a cation and an anion. To write the names just name the two ions. Easy with Representative elements. Group A NaCl = Na+ Cl- = sodium chloride MgBr2 = Mg+2 Br- = magnesium bromide Naming Binary Ionic Compounds The problem comes with the transition metals. Need to figure out their charges. The compound must be neutral. same number of + and – charges. Use the anion to determine the charge on the positive ion. Naming Binary Ionic Compounds Write the name of CuO Need the charge of Cu O is -2 copper must be +2 Copper (II) chloride Name CoCl3 Cl is -1 and there are three of them = -3 Co must be +3 Cobalt (III) chloride Naming Binary Ionic Compounds Write the name of Cu2S. Since S is -2, the Cu2 must be +2, so each one is +1. copper (I) sulfide Fe2O3 Each O is -2 Fe must be = + 3 iron (III) oxide Naming Binary Ionic Compounds Write the names of the following: KCl Na3N CrN Na2Se Ternary Ionic Compounds Will have polyatomic ions At least three elements name the ions NaNO3 CaSO4 CuSO3 (NH4)2O Ternary Ionic Compounds LiCN Fe(OH)3 (NH4)2CO3 NiPO4 Writing Formulas The charges have to add up to zero. Get charges on pieces. Cations from name of table. Anions from table or polyatomic. Balance the charges by adding subscripts. Put polyatomics in parenthesis. Writing Formulas Write the formula for calcium chloride. Calcium is Ca+2 Chloride is Cl-1 Ca+2 Cl-1 CaCl2 Write the formulas for these Lithium sulfide tin (II) oxide tin (IV) oxide Magnesium fluoride Copper (II) sulfate Iron (III) phosphide gallium nitrate Iron (III) sulfide Write the formulas for these Ammonium chloride ammonium sulfide barium nitrate Things to look for If cations have (), the number is their charge. Transition metal If anions end in -ide they are probably off the periodic table (Monoatomic) If anion ends in -ate or -ite it is polyatomic Molecular Compounds Molecular compounds made of just nonmetals smallest piece is a molecule can’t be held together because of opposite charges can’t use charges to figure out how many of each atom Easier Ionic compounds use charges to determine how many of each Have to figure out charges Have to figure out numbers Molecular compounds name tells you the number of atoms Uses prefixes to tell you the number Prefixes 1 mono2 di3 tri4 tetra5 penta6 hexa7 hepta8 octa- Prefixes 9 nona10 decaOne exception is we don’t write mono- if there is only one of the first element. Name These N2O NO2 Cl2O7 CBr4 CO2 BaCl2 Write formulas for these diphosphorus pentoxide tetraiodide nonoxide sulfur hexaflouride nitrogen trioxide Carbon tetrahydride phosphorus trifluoride aluminum chloride Naming Acids a little tricky so pay attention Acids Compounds that give off hydrogen ions when dissolved in water Must have H in them (somewhere) will always be some H next to an anion The anion determines the name. Naming acids If the anion attached to hydrogen ends in -ide, put the prefix hydro- and change -ide to -ic acid HCl - hydrogen ion and chloride ion hydrochloric acid H2S hydrogen ion and sulfide ion hydrosulfuric acid Naming Acids If the anion has oxygen in it it ends in -ate or -ite change the suffix -ate to -ic acid HNO3 Hydrogen and nitrate ions Nitric acid change the suffix -ite to -ous acid HNO2 Hydrogen and nitrite ions Nitrous acid Name these HF H3P H2SO4 H2SO3 HCN H2CrO4 Writing Formulas Hydrogen will always be first name will tell you the anion make the charges cancel out. Starts with hydro- no oxygen, -ide no hydro, -ate comes from -ic, -ite comes from -ous Write formulas for these hydroiodic acid acetic acid carbonic acid phosphorous acid hydrobromic acid