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EIT Chemistry Review S2012 Dr. Mack Chemistry is really… Chem is try To do chemistry, you must: Download available at: Practice www.csus.edu/indiv/m/mackj/ Practice Or look for Jeffrey Mack under CSUS faculty web pages Practice Part 1 1 Where do we begin… The Periodic Table 3 The Modern Periodic Table The modern organization of the periodic table came about as a result of the work of Dimitri Mendeleyev Characteristics: •Ordered elements by atomic mass •Repeating pattern of properties •Elements with similar properties in the same column Periodic Law – when the elements are arranged in order of increasing atomic mass, certain sets of properties recur periodically. Patterns used to predict properties of undiscovered elements 4 6 1 The Periodic Table: Metals and Nonmetals s ta l e nm No Metaloids ids llo i ta ” me em tors s “ uc nd co Metals The Periodic Table: 7 8 The modern periodic table is defined by: Groups (families) (columns down) Tin is in group 4A (14) in the 5th period. Periods (rows across) 9 10 2 Today’s Periodic table inert or “noble” gasses: Group 1A elements are also know as the ““Alkali Metals” Alkali Metals” as they form basic salts Metals form Cations Cations non‐metals form anions anions Metalloids can do both 11 Today’s Periodic table 12 Today’s Periodic table Group 2A elements are also know as the ““Alkaline earth Metals” Metals” as they are only found in the ground as metal salts (carbonates) 13 Group 2B – 8B elements are also know as the ““Transition Metals” Transition Metals”. They may be found in the earth as pure metals or as ores (salts). 14 3 Today’s Periodic table Today’s Periodic table Group 7A elements are also know as the ““Halogens” Halogens”. They form acids with hydrogen and exist as diatomic molecules. (F2, Cl2…) Group 8A elements are also know as the ““Noble gasses” Noble gasses”. They are inert to reaction for the most part. He is found underground! 15 16 Why do scientists use chemical symbols like C, Al and The Representation of Matter: Fe to represent atoms? In chemistry we use chemical formulas and symbols to represent matter. Why? Because atoms are really small! We are “macroscopic”: large in size on the order of 100’s of cm 10‐2 m Atoms and molecules are “microscopic”: on the order of 10‐12 cm 108 Angstroms 17 1Angstrom = 10‐10 m 18 4 Chemical Symbols and Formulas: Chemical Symbols and Formula: To what we can’t see! What we observe… Elements: H = hydrogen O = oxygen C = carbon Molecules: H2 = hydrogen O2 = oxygen some of the names are not systematic! Chemical symbols (H2O) allow us to connect… H2O = water Uh‐ Uh‐Oh! this is confusing… this is confusing… Yes it is… Yes it is… Get over it and get used to it! CH4 = methane 19 Al B Cr Co Cu F Fe Au Pb Ag Hg P K Na S 20 Atoms, Compounds, Molecules and Ions: Aluminum Boron Chromium Cobalt Copper Fluorine Iron Gold Lead Silver Mercury Phosphorus Potassium Sodium Sulfur An atom atom is the smallest indivisible indistinguishable unit of a pure element. An ion ion is an atom (or molecule) with a formal electrical charge. An anion anion is an atom (or molecule) that has a negative charge. The number of electrons > number of protons A cation cation is an atom (or molecule) has a positive charge The number of electrons < number of protons 21 22 5 Compounds: Molecules and Ionic Compounds: A compound is a distinct substance that contains two or more elements combined in a definite proportion by weight. A molecule is the smallest uncharged individual unit of a compound formed by two or more atoms. Atoms of the elements that constitute a compound are always present in simple whole number ratios. They are never present as fractional parts. Examples: AB Never: A2B Ionic compounds are made of positively and negatively charged ions. A molecule molecule can exist as an entity on its own. AB2 An ionic compound ionic compound is represented by a formula unit that describes the simplest ratio of cations to anions. A½B 23 24 Compounds fall into one of two classes: Ionic or Inorganic Compounds: Inorganic Salts Molecules metal cation non‐metal + + non‐metal or polyatomic anion non‐metal (no cations or anions) Metals and Nonmetals 1 IA 1 18 VIIIA 2 IIA 13 IIIA 2 3 4 5 6 3 IIIB 4 IVB 5 VB 6 VIB 7 VIIB 8 9 VIIIB 10 Metals Cations 11 IB 12 IIB 14 IVA 15 VA 16 VIA 17 VIIA s ta l e nm ns No Anio 7 The two use different formalisms for naming… 25 26 6 Chemical Nomenclature: Molecular Compounds: Nonmetals and Nonmetals 1 IA 1 18 VIIIA 2 IIA 13 IIIA 14 IVA 15 VA 16 VIA 17 VIIA Go to the lab page on my website and download the worksheet! 2 3 IIIB 3 4 IVB 5 VB 6 VIB 7 VIIB 8 9 VIIIB 10 11 IB s ta l e nm No 12 IIB 4 5 6 7 27 Ion Charges: 28 Binary Compounds: Metal & non‐Metal +1 +3 ‐3 ‐2 Metal of fixed oxidation (charge) state combined with a non‐metal. ‐1 +2 non‐metal takes on “ide” suffix Examples: Variable 29 Cation Anion Formula Name K+ Cl− KCl Ca2+ O2‐ CaO Calcium Oxide Na+ S2‐ Na2S Sodium sulfide Al3+ S2‐ Al2S3 Aluminum sulfide Potassium chloride 30 7 Metals of variable charge (transition) with a non‐metal Examples: Some common polyatomic ions: modify transition metal name with roman numeral Cation Anion Pb2+ Cl− Formula Name PbCl2 lead (II) chloride NH4+ H3O+ CO32– HCO32– NO2– NO3– SO42– SO32– PO43– C2H3O2– pronounced: lead ‐ lead ‐ two ‐ two ‐ chloride Pb4+ Cl− PbCl4 lead (IV) chloride Fe3+ O2− Fe2O3 Iron (III) oxide ammonium hydronium carbonate hydrogen carbonate or bicarbonate nitrite nitrate sulfate sulfite phosphate acetate 31 Ternary Compounds: Those with three different elements metal of fixed charge with a complex ion Cation Anion Formula 33 Metal of variable charge transition with a complex ion Cation Anion Formula Name Name K+ OH− KOH Potassium hydroxide Ca2+ OH− Ca(OH)2 Calcium hydroxide Na+ SO 24− Na2SO4 Sodium sulfate Al3+ SO 24− Al2(SO4)3 Aluminum sulfate 34 Fe3+ NO3− Fe(NO3)3 Iron (III) nitrate Fe2+ NO −2 Fe(NO2)2 Iron (II) nitrite 35 8 Examples: Formula Name: Non‐ Non‐metal with a non‐ metal with a non‐metal When non‐metals combine, they form molecules. They may do so in multiple forms: CO CO2 Because of this we need to specify the number of each atom by way of a prefix. BCl3 boron trichloride SO3 sulfur trioxide NO nitrogen monoxide we don’t write: 1 = mono 2 = di 5 = penta 3 = tri 6 = hexa 4 = tetra N2O4 7 = hepta nitrogen monooxide or mononitrogen monoxide dinitrogen tetraoxide 36 37 Writing formulas for acids and Bases CO2 carbon dioxide carbon monoxide CO P2O5 diphosphorous pentaoxide nitrogen trihydride NH3 •An acid acid is a substance that produces H+ when dissolved in water. •Certain gaseous molecules become acids when dissolved in water. •A base base produces OH− when dissolved in water. •Bases often are Group I and Group II hydroxide salts. (ammonia) 38 39 9 H+ and S2‐ Type I Acids: Acids derived from – –ide anions. it takes 2 H+ to cancel one S2‐ The names for these acids follows the formula: “hydro” + the root of the ide anion + ic “acid” Anion: Acid: chloride HCl hydrochloric acid fluoride HF hydrofluoric acid H2S Name: hydro sulfuric acid 40 Examples: Oxy Acids: Those derived from –ate anions. Anion: Acid: Name: NO3− HNO3 nitric acid − (chlorate) ClO3 HClO3 chloric acid (sulfate) SO24 − H2SO4 sulfuric acid (acetate) C2 H 3O2− HC2H3O2 acetic acid vinegar (nitrate) 41 Oxy Acids: Those derived from –ite anions. root name of the anion with –ous replacing the ‐ite Anion: 42 Acid: Name: (nitrite) NO2− HNO2 nitrous acid (chlorite) ClO2− HClO2 chlorous acid (sulfite) SO32 − H2SO3 sulfurous acid 43 10 Common Names: Bases: Ba(OH)2 barium hydroxide sodium hydroxide NaOH NH4OH ammonium hydroxide H2O water ammonia NH3 CH4 methane NO nitric oxide N2O nitrous oxide 44 45 Modern Atomic Theory: Practice: •Atoms are made of protons, neutrons and electrons. N2SO4 sodium sulfate barium carbonate BaCO3 FeO Iron (II) oxide zinc phosphide Zn3P2 The charge on the proton is +1 NiBr2 nickel (II) bromide There is no charge on the neutron •The nucleus of the atom carries most of the mass. • It consists of the protons and neutrons surrounded by a cloud of electrons. The charge on the electron is –1 The Atomic Number Atomic Number or number of protons in the nucleus defines an element. 47 48 11 The Composition of an Atom: Atomic Number, Z An element’s identity is defined by the number of protons in the nucleus: Z The atom is mostly empty space Atomic number 13 •protons and neutrons in the nucleus. Al •the number of electrons is equal to the number of protons. Atom symbol 26.981 Atomic weight •electrons in space around the nucleus. 49 Ch. 2 Isotopes, Atomic Numbers, and Mass Numbers 50 Example: Selenium‐75 Elemental Isotopic Symbols: For a given element “XX”, an isotope is written by: Atomic number (Z) = number of protons in the nucleus. 75 protons + neutrons Mass number (A) = total number of nucleons in the nucleus (i.e., protons and neutrons). 75 34 Se 34 protons One nucleon has a mass of 1 amu (Atomic Mass Unit Atomic Mass Unit) a.k.a “Dalton Dalton” or u A Z X Isotopes have the same Z but different total number of nucleons (A). 51 protons = 34 electrons = 34 neutrons = 75‐34 = 41 52 12 Ch. 2 The average weighted atomic mass is determined by the following mathematical expression: Average mass of a Cl atom mass of a Cl‐35 atom m Cl (u) = m Cl‐35 × fraction that are Cl‐35 mass of a Cl‐37 atom abundance + m Cl‐37 × of Cl‐35 Avogadro’s Number and the Mole Ch. 2 The concept of a mole is defined so that we may equate the amount of matter (mass) to the number of particles (mole). fraction that are Cl‐37 abundance of Cl‐37 The Standard is based upon the C‐12 isotope. The mass of one 12C‐atom is 1.99265 × 10‐23 g. 35.45 u = 34.96885u × 0.7553 + 36.96590 × 0.2447 The atomic mass of 12C is defined as exactly 12 u. (4 sig. fig) This is the value that is reported on the periodic table. Note that: 0.7553 + 0.2447 = 1.0000 (100%) Therefore: 1u = (the mass of one 12C atom ÷12) = 1.66054 × 10‐24g = 1.66054 × 10‐27 kg 53 Ch. 2 Avagagro’s Number 54 Ch. 2 Molar Masses Since we can equate mass (how much matter) with moles (how many particles) we now have a conversion factor that relates the two. Since one mole of 12C has a mass of 12g (exactly), 12g of 12C contains 6.022142 × 1023 C‐12 atoms. But carbon exists as 3 isotopes: C‐12, C‐13 &C‐14 mols The average atomic mass of carbon is 12.011 u. molar mass (g/mol) = grams The Molar Mass of a substance is the amount of matter that contains one‐mole or 6.022 × 1023 particles. From this we conclude that 12.011g of carbon contains 6.022142 × 1023 C‐atoms × aka: Avogadro's number (N Avogadro's number (NA) Is this a valid assumption? The atomic masses on the Periodic Table also represent the molar masses of each element in grams per mole (g/mol) Yes, since NA is so large, the statistics hold. 55 56 13 So if you have 12.011g of carbon… you have 6.022×1023 carbon atoms! Ch. 2 Grams, Moles and Molar Mass: The molar mass of an atom is a conversion factor that relates mass (grams) to moles moles and vice versa. So if you have 39.95g of argon… you have 6.022×1023 argon atoms! (how much matter) (number of atoms) grams ÷ molar mass = moles if you have a mole of dollar bills… g × you are Bill Gates… you have 6.022×1023 bucks! mol = mol g Avogadro's number (NA) relates moles numbers of individual particles: and if you have 6.022×1023 avocados… you have… 1 mol × a “guacamole” 6.022 × 1023 particles = 6.022 × 1023 particles mol 58 Question: How many magnesium atoms are there in 150.0 g of Question: magnesium? Ch. 2 Ch. 2 The molar mass of an ionic compound is the molar mass of one formula unit of the compound. Solution: Use the molar mass of Mg from the periodic table. 150.0g Mg × 59 For the compound Al2(SO4)3 the molar mass would be: 1 mol Mg 6.022 x 1023 Mg atoms × 24.305g Mg 1 mol Mg 2 × (26.98 g/mol) = 3.717 × 1024 Mg atoms (4 sig figs) big number as expected! 2 Al’s + 3 × (32.07 g/mol) 3 S’s + 3 × 4 × (16.00g/mol) 3 × 4 O’s 342.17 g/mol 60 62 14 How many oxygen atoms are there in 25.1g of chromium (III) acetate? (a) How many grams of nitrogen will be needed to produce 0.384 mols of ammonia? step 1: write the correct chemical formula… Cr3+ & C2H3O2− step 2: calculate the molar mass… 3 2(g) N2(g) + H Cr(C2H3O2)3 229.13 g/mol 0.384 mols NH3 × step 3: use dimensional analysis to solve the problem… 3×2 = 6 25.1g Cr(C 2 H3O 2 )3 × 1mol Cr(C 2 H3O 2 )3 229.13g Cr(C2 H 3O 2 )3 6.022 × 1023 O − atoms × = 1mol O 6mol O × 1mol Cr(C 2 H 3O 2 )3 3.96 × 1023 1mol N 2 28.02g N 2 × 2mol NH 3 1mol N 2 = 5.38g N2 (b) How many moles of hydrogen are needed to combine with 5.84g of nitrogen? 5.84g N 2 × O‐atoms 3 sf 3 sf 2 NH3(g) 1mol N 2 3mol H 2 × = 0.625mols H 2 28.02 gN 2 1mol N 2 Ch. 2 63 How many grams of nitrogen are needed to completely react with 0.525 g of hydrogen in the formation of ammonia? 64 How many grams of nitrogen are needed to completely react with 0.525 g of hydrogen in the formation of ammonia? To answer this question, one must go through moles. 3 2(g) N2(g) + H 3 2(g) N2(g) + H 2 NH3(g) 0.525gH 2× The equation relates moles, not mass. 2 NH3(g) 1 mol H 2 1mol N 2 28.02g N 2 × × = 2.43g N 2 2.02g H 2 3mol H 2 1mol N 2 How many grams of ammonia form? g H2 mols H2 mols N2 g N2 0.525gH 2× 65 1 mol H 2 2 mol NH 3 17.04g NH 3 × × = 2.95g NH 3 1mol NH 3 2.02g H 2 3mol H 2 66 15 How many grams of O2 will result form the decomposition of 15.6g of potassium chlorate? Step 1. How many grams of O2 will result form the decomposition of 15.6g of potassium chlorate? Write the chemical equation 2 KClO3(s) 3 O2(g) 2 KClO3(s) 3 O2(g) + KCl(s) 2 + KCl(s) 2 Step 2: Balance 15.6g KClO3× 1mol KClO3 3mol O2 32.00g O2 × × 122.55g KClO3 2mol KClO3 1mol O2 Step 3: Set up the solution g KClO3 mols KClO3 mols O2 = 61.1g O2 g O2 67 Chemical Reactions Ch. 3 A chemical reaction chemical reaction can be described by a chemical equation chemical equation. All chemical equations have three parts: Reactants Æ 68 How does one know when a reaction has occurred? Generally, what you end up with looks nothing like what you started with. Before Ch. 3 After Products When a chemical changes occurs: Atoms, Compounds or Molecules Æ New Compounds, Molecules or atoms 69 70 16 Indicators of a Chemical Reaction: Ch. 3 Gas Evolution Indicators of a Chemical Reaction: Temperature change 71 Indicators of a Chemical Reaction: Ch. 3 Ch. 3 Color Change 72 Indicators of a Chemical Reaction: Ch. 3 Precipitate Formation 73 74 17 The chemical equation for the formation of water can be visualized as two hydrogen molecules reacting with one oxygen molecule to form two water molecules: Quantitative Information About Chemical Reactions Mass must be conserved in a chemical reaction. Total mass of reactants 2H2 + O2 → 2H2O Total mass of products = Chemical equations must therefore be balanced for mass. Numbers of atoms on the reactant side Numbers of atoms on the product side = 11.2g + 88.8g → 100.0g mass is conserved! 76 When writing chemical reactions one starts with: Balancing Chemical Reactions: Example C2H6 + 2 C’s & 6 H’s → O2 2 O’s balance last CO2 + Reactants H2O 1 C & 2 O’s + N2(g) + 3H2(g) → O2 CO2 Ch. 3 products 2 H’s & 1 O balance H first 2 2H6 ___C 77 3 2O 6 ___ H + 2NH3(g) Some reactions can also run in reverse: balance C next 2C2H6 + O2 → 4 2 ___ CO + 6H2O 2NH3(g) balance O 2C2H6 + 4 C’s 7 2 ____ O 12 H’s 14 O’s → 4CO2 + 4 C’s N2(g) + 3H2(g) Under these conditions, the reaction can be written: 6H2O 3H2 (g) + N2 (g) R 2NH3 (g) 12 H’s 14 O’s Dynamic Equilibrium! 78 79 18