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1 EIT Chemistry Review S01 Dr. Mack Chemistry is really Chem is try Download available at: Or look for Jeffrey Mack under CSUS faculty web pages Part 1 To do chemistry, you must: Practice Practice Practice 1 Where do we begin The Periodic Table The Modern Periodic Table The modern organization of the periodic table came about as a result of the work of Dimitri Mendeleyev 4 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 6 1

2 The Periodic Table: Metals and Nonmetals The Periodic Table: Metaloids Metals Nonmetals metalloids metalloids semi conductors 7 8 The modern periodic table is defined by: Groups (families) (columns down) Tin is in group 4A (14) in the 5 th period. Periods (rows across) 9 10

3 inert or noble gasses: Today s Periodic table Group 1A elements are also know as the Alkali Metals as they form basic salts Metals form Cations non metals form anions Metalloids can do both 11 1 Today s Periodic table Today s Periodic table Group A elements are also know as the Alkaline earth Metals as they are only found in the ground as metal salts (carbonates) Group B 8B elements are also know as the Transition Metals. They may be found in the earth as pure metals or as ores (salts). 1 14

4 Today s Periodic table Group 7A elements are also know as the Halogens. They form acids with hydrogen and exist as diatomic molecules. (F, Cl ) Today s Periodic table Group 8A elements are also know as the Noble gasses. They are inert to reaction for the most part. He is found underground! The Representation of Matter: In chemistry we use chemical formulas and symbols to represent matter. Why? We are macroscopic : large in size on the order of 100 s of cm Atoms and molecules are microscopic : on the order of 10 1 cm Why do scientists use chemical symbols like C, Al and Fe to represent atoms? Fe Because atoms are really small! 10 m 10 8 Angstroms 1Angstrom = m

5 Chemical Symbols and Formulas: What we observe To what we can t see! Chemical symbols (H O) allow us to connect Chemical Symbols and Formula: Elements: H = hydrogen O = oxygen C = carbon Molecules: H = O = hydrogen oxygen some of the names are not systematic! H O = CH 4 = water methane Uh Oh! this is confusing Yes it is Get over it and get used to it! 19 0 Al B Cr Co Cu F Fe Au Pb Ag Hg P K Na S Aluminum Boron Chromium Cobalt Copper Fluorine Iron Gold Lead Silver Mercury Phosphorus Potassium Sodium Sulfur Atoms, Compounds, Molecules and Ions: An atom is the smallest indivisible indistinguishable unit of a pure element. An ion is an atom (or molecule) with a formal electrical charge. An anion is an atom (or molecule) that has a negative charge. The number of electrons > number of protons A cation is an atom (or molecule) has a positive charge The number of electrons < number of protons 1 5

6 Compounds: A compound is a distinct substance that contains two or more elements combined in a definite proportion by weight. Atoms of the elements that constitute a compound are always present in simple whole number ratios. They are never present as fractional parts. Examples: Never: AB A B AB A ½ B Molecules and Ionic Compounds: A molecule is the smallest uncharged individual unit of a compound formed by two or more atoms. Ionic compounds are made of positively and negatively charged ions. A molecule can exist as an entity on its own. An ionic compound is represented by a formula unit that describes the simplest ratio of cations to anions. 4 Compounds fall into one of two classes: Inorganic Salts metal cation + non metal or polyatomic anion Molecules non metal + non metal (no cations or anions) The two use different formalisms for naming Ionic or Inorganic Compounds: Metals and Nonmetals 1 IA IIA IIIB 4 IVB VB VIB VIIB VIIIB Metals Cations IB 1 IIB 1 IIIA 14 IVA 15 VA 16 VIA 17 VIIA 18 VIIIA Nonmetals Anions 5 6 6

7 1 Molecular Compounds: Nonmetals and Nonmetals 1 IA IIA 1 IIIA 14 IVA 15 VA 16 VIA 17 VIIA 18 VIIIA Chemical Nomenclature: Go to the lab page on my website and download the worksheet! 4 5 IIIB 4 IVB 5 VB 6 VIB 7 VIIB 8 9 VIIIB IB 1 IIB Nonmetals Ion Charges: Binary Compounds: Metal & non Metal Metal of fixed oxidation (charge) state combined with a non metal. Examples: non metal takes on ide suffix Cation Anion Formula Name Variable K + Cl KCl Potassium chloride Ca + O CaO Calcium Oxide Na + S Na S Sodium sulfide Al + S Al S Aluminum sulfide 9 0 7

8 Metals of variable charge (transition) with a non metal Examples: modify transition metal name with roman numeral Cation Anion Formula Name Pb + Cl PbCl lead (II) chloride pronounced: lead two chloride Pb 4+ Cl PbCl 4 lead (IV) chloride Fe + O Fe O Iron (III) oxide Some common polyatomic ions: NH 4 + H O + CO HCO NO NO SO 4 SO PO 4 C H O ammonium hydronium carbonate hydrogen carbonate or bicarbonate nitrite nitrate sulfate sulfite phosphate acetate 1 Ternary Compounds: Those with three different elements metal of fixed charge with a complex ion Cation Anion Formula Name K + OH KOH Potassium hydroxide Ca + OH Ca(OH) Calcium hydroxide Metal of variable charge transition with a complex ion Cation Anion Formula Name Fe + NO Fe(NO ) Iron (III) nitrate Fe + NO Fe(NO ) Iron (II) nitrite Na + SO 4 Na SO 4 Sodium sulfate Al + SO 4 Al (SO 4 ) Aluminum sulfate 4 5 8

9 Non metal with a non metal When non metals combine, they form molecules. They may do so in multiple forms: CO CO Because of this we need to specify the number of each atom by way of a prefix. 1 = mono = di = tri 4 = tetra Examples: Formula Name: BCl SO NO we don t write: boron trichloride sulfur trioxide nitrogen monoxide nitrogen monooxide or mononitrogen monoxide 5 = penta 6 = hexa 7 = hepta N O 4 dinitrogen tetraoxide 6 7 CO carbon monoxide P O 5 carbon dioxide CO diphosphorous pentaoxide Writing formulas for acids and Bases An acid is a substance that produces H + when dissolved in water. Certain gaseous molecules become acids when dissolved in water. nitrogen trihydride NH (ammonia) A base produces OH when dissolved in water. Bases often are Group I and Group II hydroxide salts

10 Type I Acids: Acids derived from ide anions. The names for these acids follows the formula: hydro + the root of the ide anion + ic acid Anion: Acid: Name: chloride HCl hydrochloric acid H + and S H S it takes H + to cancel one S hydrosulfuric acid fluoride HF hydrofluoric acid Examples: Anion: Acid: Name: (nitrate) NO HNO nitric acid (chlorate) ClO HClO chloric acid (sulfate) Oxy Acids: Those derived from ate anions. SO 4 H SO 4 sulfuric acid (acetate) CHO HC H O acetic acid vinegar Oxy Acids: Those derived from ite anions. root name of the anion with ous replacing the ite Anion: Acid: Name: (nitrite) NO HNO nitrous acid (chlorite) ClO HClO chlorous acid (sulfite) SO H SO sulfurous acid

11 Bases: Common Names: Ba(OH) barium hydroxide H O water sodium hydroxide NaOH ammonia NH NH 4 OH ammonium hydroxide CH 4 NO methane nitric oxide N O nitrous oxide Practice: Modern Atomic Theory: N SO 4 sodium sulfate barium carbonate BaCO FeO Iron (II) oxide zinc phosphide Zn P NiBr nickel (II) bromide Atoms are made of protons, neutrons and electrons. 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 charge on the proton is +1 There is no charge on the neutron The Atomic Number or number of protons in the nucleus defines an element

12 The Composition of an Atom: The atom is mostly empty space Atomic Number, Z An element s s identity is defined by the number of protons in the nucleus: Z protons and neutrons in the nucleus. the number of electrons is equal to the number of protons. electrons in space around the nucleus Al Atomic number Atom symbol Atomic weight 50 Isotopes, Atomic Numbers, and Mass Numbers Ch. Example: Selenium 75 Elemental Isotopic Symbols: For agiven element X, an isotope is written by: Atomic number (Z) = number of protons in the nucleus. Mass number (A) = total number of nucleons in the nucleus (i.e., protons and neutrons). One nucleon has a mass of 1 amu (Atomic Mass Unit) a.k.a Dalton or u A Z X Isotopes have the same Z but different total number of nucleons (A). 75 protons + neutrons 4 protons 75 4Se protons = 4 electrons = 4 neutrons = 75 4 =

13 The average weighted atomic mass is determined by the following mathematical expression: Average mass of a Cl atom m Cl (u) = m Cl 5 abundance of Cl u (4 sig. fig) mass of a Cl 5 atom fraction that are Cl 5 mass of a Cl 7 atom + m Cl 7 fraction that are Cl 7 abundance of Cl 7 = u This is the value that is reported on the periodic table. Note that: = (100%) Ch. Avogadro s Number and the Mole The concept of a mole is defined so that we may equate the amount of matter (mass) to the number of particles (mole). The Standard is based upon the C 1 isotope. The mass of one 1 C atom is g. The atomic mass of 1 C is defined as exactly 1 u. Therefore: 1u = (the mass of one 1 C atom 1) = g = kg Ch Avagagro s s Number Ch. Molar Masses Ch. Since one mole of 1 C has a mass of 1g (exactly), 1g of 1 C contains C 1 atoms. Since we can equate mass (how much matter) with moles (how many particles) we now have a conversion factor that relates the two. But carbon exists as isotopes: C 1, C 1 &C 14 mols molar mass (g/mol) = grams The average atomic mass of carbon is u. From this we conclude that 1.011g of carbon contains C atoms Is this a valid assumption? Yes, since N A is so large, the statistics hold. 55 The Molar Mass of a substance is the amount of matter that contains one mole or particles. aka: Avogadro's number (N A ) The atomic masses on the Periodic Table also represent the molar masses of each element in grams per mole (g/mol) 56 1

14 So if you have 1.011g of carbon you have carbon atoms! So if you have 9.95g of argon you have argon atoms! if you have a mole of dollar bills you are Bill Gates you have bucks! and if you have avocados you have a guacamole Ch. 58 Grams, Moles and Molar Mass: The molar mass of an atom is a conversion factor that relates mass (grams) to moles and vice versa. (how much matter) (number of atoms) grams molar mass = moles mol g = g mol Avogadro's number (N A ) relates moles numbers of individual particles: particles 1 mol = particles mol 59 Question: How many magnesium atoms are there in g of magnesium? Solution: Use the molar mass of Mg from the periodic table. 1mol Mg 150.0g Mg 4.05g Mg 6.0 x 10 Mg atoms 1mol Mg 4 = Mg Ch. atoms The molar mass of an ionic compound is the molar mass of one formula unit of the compound. For the compound Al (SO 4 ) the molar mass would be: (6.98 g/mol) Al s + (.07 g/mol) S s + 4 (16.00g/mol) 4 O s Ch. (4 sig figs) big number as expected! 4.17 g/mol

15 How many oxygen atoms are there in 5.1g of chromium (III) acetate? step 1: write the correct chemical formula Cr + & C H O Cr(C H O ) (a) How many grams of nitrogen will be needed to produce 0.84 mols of ammonia? N (g) + H (g) NH (g) step : calculate the molar mass 9.1 g/mol step : use dimensional analysis to solve the problem 5.1g Cr(CHO ) 1mol Cr(CHO ) 9.1g Cr(C H O ) O atoms = 6 6mol O 1mol Cr(C H O ) = mol O O atoms sf Ch. 6 1mol N 0.84 mols NH mol NH 8.0g N = 5.8g N 1mol N (b) How many moles of hydrogen are needed to combine with 5.84g of nitrogen? 5.84g N 1mol N mol H 8.0 gn 1mol N = 0.65mols H 64 How many grams of nitrogen are needed to completely react with 0.55 g of hydrogen in the formation of ammonia? To answer this question, one must go through moles. N (g) + H (g) NH (g) The equation relates moles, not mass. g H mols H mols N g N How many grams of nitrogen are needed to completely react with 0.55 g of hydrogen in the formation of ammonia? N (g) + H (g) NH (g) 1 mol H 1mol N 0.55gH.0g H mol H How many grams of ammonia form? 8.0g N 1mol N =.4g N 1 mol H mol NH 17.04g NH 0.55gH =.95g NH.0g H mol H 1mol NH

16 How many grams of O will result form the decomposition of 15.6g of potassium chlorate? How many grams of O will result form the decomposition of 15.6g of potassium chlorate? Step 1. Write the chemical equation KClO (s) O (g) + KCl(s) KClO (s) O (g) + KCl(s) Step : Balance Step : Set up the solution 1mol KClO mol O.00g O 15.6g KClO 1.55g KClO mol KClO 1mol O g KClO mols KClO mols O g O = 61.1g O Chemical Reactions A chemical reaction can be described by a chemical equation. All chemical equations have three parts: Ch. How does one know when a reaction has occurred? Generally, what you end up with looks nothing like what you started with. Before After Ch. Reactants Products When a chemical changes occurs: Atoms, Compounds or Molecules New Compounds, Molecules or atoms

17 Indicators of a Chemical Reaction: Ch. Indicators of a Chemical Reaction: Ch. Gas Evolution Temperature change 71 7 Indicators of a Chemical Reaction: Ch. Indicators of a Chemical Reaction: Ch. Color Change Precipitate Formation

18 Quantitative Information About Chemical Reactions Mass must be conserved in a chemical reaction. 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: Total mass of reactants = Total mass of products H + O H O Chemical equations must therefore be balanced for mass. Numbers of atoms on the reactant side = Numbers of atoms on the product side g g 100.0g mass is conserved! 77 Balancing Chemical Reactions: Example When writing chemical reactions one starts with: Ch. C H 6 + O CO + H O Reactants products C s & 6 H s O s 1 C & O s H s & 1 O balance last balance H first C H 6 + O CO + H O balance C next C H 6 + O CO + 6H O 4 6 N (g) + H (g) NH (g) Some reactions can also run in reverse: NH (g) N (g) + H (g) balance O 7 C H 6 + O 4CO + 6H O 4 C s 1 H s 14 O s 4 C s 1 H s 14 O s Under these conditions, the reaction can be written: H (g) + N (g) NH (g) Dynamic Equilibrium!