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ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES CHAPTER 2 Molecules (pp. 40-50) 1 What is a molecule? Only a few elements, such as _________________ and __________________, exist in their pure form on Earth. Most atoms combine with atoms of other _____________________ to form ___________________________. A molecule is a group of __________ or more atoms that are _____________________ bonded together. Examples: - O2 - _____________ - H2O - _____________ - NaCl - _____________ Why do atoms tend to bond with other atoms? ______________________________________________________________________________ ______________________________________________________________________________ Noble gases (Group VIII) have a _____________ valence shell; therefore they are extremely _________________ and rarely ________________ with other elements. Halogens (Group VII) have _______ valence electron, so they need to ____________ one electron to acquire the electron configuration of the nearest noble gas. Alkali metals (Group I) have only ________ valence electron, so they all tend to _________ that electron to resemble a noble gas. 1 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES Table 2.4: THE TENDENCY OF GROUP A ELEMENTS TO GAIN OR LOSE ELECTRONS Group # IA IIA IIIA IVA VA VIA VIIA VIIIA Element example Li Be B C N O F Ne # valence electrons Tendency Octet Rule: The tendency of elements to acquire the configuration of the noble gas __________________ to them in order to have ____________ electrons in their valence shell. (Exceptions: Li, ______, and ______ acquire the configuration of ______________ and thus follow the ___________ rule.) *Special case: ___________________ - depending on the circumstances it can _________ its only electron or it can __________ a second electron. 1.1 IONS In general atoms are electrically ____________________ (equal # of _____ & _____ ) An ion is an atom that has become electrically ___________________ by ________________ or _____________________ one or more electrons. ION FORMATION IN METALS Since alkali metals (Group I) have only ________ valence electron, they all tend to _________ that electron when forming ions. When this happens, they acquire a charge of _________. 2 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES http://www.nios.ac.in/images/5.1.gif Since alkaline earth metals (Group II) have ________ valence electrons, they all tend to _________ _____ electrons when forming ions. When this happens, they acquire a charge of _________. All metals ____________ their valence electrons when forming ions and thus form _____________________ charged ions (CATIONS). ION FORMATION IN NON-METALS Since halogens (Group VII) have ________ valence electrons, they all tend to _____________ _________ electron when forming ions. When this happens, they acquire a charge of _________. Because non-metals all have ______ or more valence electrons, they all _____________ electrons when forming ions and thus form _____________________ charged ions (ANIONS). 3 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES 1.2 The Nature of Chemical Bonds (EST ONLY) Most atoms, except those of noble gases, have a natural tendency to ____________ or _________ electrons in order to fill their outer shells. When two atoms come together, they will either ___________________ or ___________________ their valence electrons to become _________________. A __________________ _________________ is the union of two atoms through the ___________________ or _______________________ of one or more electrons. There are _______________ main types of chemical bonds: ___________________ bonds and ______________________ bonds. IONIC BONDS An IONIC BOND is usually the result of a transfer of one or more _________________ from one atom (usually a ___________) to another atom (usually a ________________). The formation of an ionic bond represented with Lewis structures http://www.clickandlearn.org/Gr9_Sci/atoms/bonding.htm In the Lewis dot diagram above we see that when the sodium atom comes in contact with a chlorine atom, the sodium atom gives up an _____________________. Both atoms thus acquire an electron configuration similar to that of a ______________ gas. The sodium atom becomes a ___________________ ion (Na+), and the chlorine atom, a negative ion (Cl-). Since positive and 4 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES negative charges _______________ each other, the positive sodium and the negative chloride ion come together to form a _______________________ compound. In the space below, draw the Rutherford-Bohr Atomic Model showing the formation of an ionic bond between Magnesium and Bromine (MgBr2). COVALENT BONDS Molecular oxygen (O2), ammonia (NH3), and methane (CH4) are examples of the type of bonding where an electron _____________________ reacts with another ________________. A COVALENT BOND is the result of the _____________________ of one or more electron _______________ between two ______________________ atoms. When molecular fluorine (F2) is formed, each atom _____________ an electron with another fluorine atom so they both have the electron configuration of __________, the nearest Noble gas. In the Lewis structure, the shared electron pair is ___________________; in the ball and stick model, it is represented by a _______________. F F 5 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES Sometimes two atoms share than one ________________ pair. In molecular ____________________ (O2), each oxygen atom needs ____________ more electrons to achieve the configuration of a ________________ gas, so ___________ oxygen atoms tend to share two electron pairs. Oxygen atoms are linked in a _________________ bond. Triple bonds, between atoms of other elements (such as _________________) are also possible. Rutherford-Bohr Atomic Model for O2 Lewis Structure for O2 Ball and Stick Atomic Model for O2 Electron pairs are not always shared ____________________. Some atoms have a ___________ force of attraction for electron pairs than others. In a _______________ molecule, the ____________atom attracts the electrons more than the two _____________________ atoms do. This causes a certain degree of ________________ polarity, with the oxygen atom carrying a slightly _____________ charge, and the hydrogen atoms, a slightly __________________ one. The charges are so small that they do not turn water into an _______________ compound. The unequal covalent bonds are referred to as __________ ___________ ___________. symbol for a partial charge O H H Diatomic molecules Some elements do not exist in nature as individual atoms. Such atoms come in pairs like socks and jeans. They are diatomic molecules (made up of 2 atoms). To recall which elements are diatomic, just remember this simple phrase: “I Have No Bright Or Clever Friends” I2, H2, N2, Br2, O2, Cl2, F2 6 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES 1.3 The Rules of Chemical Notation and Nomenclature (EST ONLY) Naming Binary Ionic Compounds A binary compound is a compound made up of _______ different elements. (bi = _______) 1. Name the metal first 2. Add the suffix –ide to the name of the non-metal Examples: NaCl __________________________________________ CaF2 __________________________________________ AgBr __________________________________________ Na3N __________________________________________ KI __________________________________________ ZnO __________________________________________ Mg3P2 __________________________________________ Writing Formulas for Binary Ionic Compounds Use the CROSS-OVER RULE!!!! The Cross-Over Rule involves writing the charge on each ion as a superscript and then crossing the numbers over and writing them as subscripts without the + and -. Don’t worry, it’s super easy! Remember to reduce to lowest terms! Example: Write the molecular formula for magnesium bromide. Mg2+ Br- MgBr2 7 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES Let’s do a few more: Aluminum oxide Sodium fluoride Calcium sulfide _____________ _____________ _____________ Stock System for Naming Ionic Compounds Containing Multi-Valent Ions Some transition metals can form ions with two different charges. Because of the existence of two different ions for these metals, we need a naming system that will enable us to distinguish one from the other. The system we will use is the Stock System. The Stock System involves writing a roman numeral after the name of the metal to distinguish it from its other ion. Examples: Fe2+ = __________________________________ Fe3+ = __________________________________ Pb2+ = __________________________________ Pb4+ = __________________________________ Cu+ = __________________________________ What do we do when we’re faced with naming this: CuCl2? Is it copper (I) chloride or copper (II) chloride? We have to do the Cross-Over Rule in reverse! Cu? ClCuCl2 Since the charge on chlorine is ______ and there are _____ chloride ions in the formula, that makes 2 × -1 = _____, so the copper has to have a charge of _______ in order for the compound to be neutral. So the name of this compound is ___________________________________________. 8 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES Let’s try a few more: Fe2O3 PbS MnO2 ___________________________ ___________________________ ___________________________ Writing Formulas for Ionic Compounds Containing Multi-Valent Ions Use the CROSS-OVER RULE just like you do for a regular ionic compound! Example: Write the molecular formula for chromium (III) chloride. Cr3+ Cl- CrCl3 Try these: Nickel (II) bromide ___________ Gold (III) oxide ___________ Mercury (II) sulfide ___________ Naming Binary Covalent Compounds Use prefixes to indicate the number of atoms of each type. DO NOT use the prefix “mono” on the first element in the formula. Table 2.18: Prefixes Indicating the Number of Atoms of an Element in a Binary Covalent Compound Number of Atoms Prefix Number of Atoms One Six Two Seven Three Eight Four Nine Five Ten Prefix 9 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES Examples: CO2 __________________________________ N2O4 __________________________________ CO __________________________________ SF6 __________________________________ PCl3 __________________________________ P4O10 __________________________________ Exceptions to naming covalent compounds Some covalent compounds have common names and are not named according to the rule above. (You must memorize the table below!) Formula Name Formula H2O CH3OH NH3 C2H5OH CH4 C6H12O6 C3H8 C12H22O11 C4H10 H2O2 Name Hydrogen compounds (ex. HCl, H2S, etc.) DO NOT take prefixes! HCl ____________________________ H2S ____________________________ POLYATOMIC IONS (EST ONLY) p. 44 A ___________________________ ION is a group of _______ or more chemically bonded atoms that has become electrically _________________________ by _____________ or ____________________ one or more electrons. 10 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES Table 2.10: Examples of Common Polyatomic Ions Chemical Formula Name CH3COO- Chemical Formula Name OHAmmonium Nitrate Bicarbonate Nitrite CO32- PO43Chlorate SO42- CrO42- Sulfite NOTE: Your teacher will ask you to memorize some of the most common polyatomic ions. Naming ionic compounds containing polyatomic ions (non-binary ionic compounds) Examples: CaCO3 ________________________________ Mg3PO4 ________________________________ NaOH ________________________________ Na2SO4 ________________________________ HCN ________________________________ NaHCO3 ________________________________ Writing formulas for ionic compounds containing polyatomic ions (non-binary ionic compounds) Use the CROSS-OVER RULE! If there is more than one polyatomic ion in the formula, you must put brackets around it. Never change the subscripts of a polyatomic ion! Ex. Ca3(PO4)2 ≠ Ca3P2O8 Example: Write the chemical formula for magnesium hydroxide. 11 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES Ammonium nitrate Potassium chromate Aluminum sulfate ___________ ___________ ___________ 2 Properties of solutions Sometimes atoms and molecules can combine without undergoing a ______________ reaction to form a ______________. Since not _____________ bonds need to be _____________, the different substances that make up a mixture can be ___________________ using physical _______________ ________________. A solution is a ___________________ mixture (consisting of at least one ________ and one ________________) whose component substances (solids, _______________ or gases) cannot be _________________, even with the aid of a magnifying instrument. Solute: The component of the substance that is ______________ in the other. Examples of solutes include salt, sugar, colouring and alcohol. Solvent: The substance in which the solute ________________. Examples of solvents include water, alcohol and acetone. Aqueous Solution: A solution in which the solvent is _________________. Water is the universal solvent because: It dissolves many substances. Molecules with _______________ bonds and molecules with a certain polarity dissolve easily in water. ________________ molecules, such as oil, rarely dissolve well in water. It is _______________ (pH = 7) _________________________ Odourless _________________________ Doesn’t react 12 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES 2.1 SOLUBILITY SOLUBILITY is the maximum amount of _________________ that can be _________________ in a certain volume of ____________________. Factors that affect solubility: _______________ of the solute _______________ of the solvent _______________________ affects solubility of gaseous solutes ________________________ (solids tend to become more ____________ as solvent temperature rises while gases tend to become less _______________ as solvent temperature rises) Figure: Solubility of Carbon Dioxide in Water as a Function of Temperature HTTP://WWW.ENGINEERINGTOOLBOX.COM/GASES-SOLUBILITY-WATER-D_1148.HTML SEE Appendix 2 on p. 516 for a list of the solubility (and other characteristic properties) of many common substances. 2.2 CONCENTRATION The CONCENTRATION of a solution is the_______________ of _______________ 13 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES in a given amount of _________________. It is the ratio of the quantity of solute to the quantity of the solution. DILUTION AND DISSOLUTION The concentration of a solution can be varied in different ways. Change Effect on the concentration Dilution (_____________ of solvent) Dissolution (addition of ________________) ___________________ (reduction of solvent) Expressing the Concentration of Aqueous Solutions 1. Concentration: Number of grams of solute per liter of solution (g/L) Application: What mass of NaOH is needed to prepare 500mL of a 4 g/L NaOH solution? 2. Mass-Volume Percent: Number of grams of solute per100 mL of solution, expressed as a percentage (% m/V) 14 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES Application: You have 24g of sugar to prepare a 6%m/V sugar solution. What volume of solution will you make? 3. Volume Percent: Number of millilitres of solute per 100 mL of solution, expressed as a percentage (% V/V) Application: a) You have 50mL to prepare a 6%V/V alcohol solution. What volume of solution will you make? b) You add 75 mL of acetone to 1205mL of water. What is the concentration of the solution in %V/V? 4. Mass Percent: Number of grams of solute per 100 mL of solution, expressed as a percentage (%m/m) Application: What is the mass of NaCl in 400g of an 8%m/m brine solution? CONCENTRATION IN PPM When the amount of solute in the solution is very small, the concentration can be expressed in _____________ _________ _________________. 15 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES The CONCENTRATION in PPM (“ __________ ____ _______________”) is the number of parts of solute in a _______________ parts of solution. 1 ppm = 1g 1mg = = 1 mg/L 1000000 g 1000 g VERY IMPORTANT!!!! X%(m/V) = X g/100mL Example: 5%(m/V) = 5g/100mL = 5000 mg/0.1 L = 50 000 mg/L or 50 000 ppm MOLAR CONCENTRATION (AKA Molarity) (EST ONLY) Expressed as moles per liter (__________________) MOLAR CONCENTRATION corresponds to the number of ____________ of dissolved solute particles in a ___________ of solution. Molar concentration is symbolized by placing the _______________ formula for the measured substance inside _________ brackets. Example [NaCl] = 0.5 mol/L means the ___________ concentration of sodium chloride solution equals _____________ mol/L. Molar concentration of a solution can be calculated using the formula: The units for molarity are mol/L or M (in this case, M is the unit for molar concentration. MC is the symbol for molar concentration.) Example: Suppose 58.5 g of sodium chloride are dissolved in 500 mL of solution. Calculate the molar concentration of this solution following the method illustrated on page 54. 16 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES More Practice a) If 20g of KNO3 is dissolved in enough water to make 500mL of solution, what is the molar concentration of the solution? (Answer 0.4M) b) What mass of CaF2 is needed to prepare 250mL of a 0.1mol/L solution? (Answer 1.95 g) The following is not covered in Chapter 2 of OBSERVATORY. It is, however, important information that you need to know for your lab exam in June. HOW TO PREPARE A SOLUTION How would you prepare 250mL of a 20 g/L solution of cobalt (II) chloride, CoCl2? 1. Calculate the mass of solute needed. 2. Using an electronic balance weigh out the mass of the solute needed. 3. Pour a small amount of water into the volumetric flask. 4. Pour the solute into the flask. 5. Add water up to etched line. Use a pipette near the end (bottom of meniscus should be on the etched line) 6. Cap the flask, invert the flask and shake. Repeat 3 times. 17 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES DILUTING SOLUTIONS To dilute a solution is simply to add ____________ to a more concentrated solution. Even after you do this, the amount of _________________ is the same in both the original concentrated solution and the new diluted solution. Recall that C = m/V, so m = C V DILUTION FORMULA mc = mass of solute in concentrated solution mc = m d md =mass of solute in diluted solution Cc Vc = Cd Vd Cc = concentration of the concentrated solution (in %m/m, %V/V, %m/V, or g/L) Cd = concentration of the diluted solution (in %m/m, %V/V, %m/V, or g/L) Vc = volume of concentrated solution (in mL or L) Vd = volume of diluted solution (in mL or L) Some tips to remember: Cc Cd (ex. 30%V/V 6%V/V) Vd = Vc + Vwater added Vc Vd (ex. 5 mL 25 mL) Vwater added = Vd - Vc Example 1: You have a bottle of 5%m/V bleach solution. You need to prepare 500 mL of a 2% m/V bleach solution. What volume of concentrated bleach will you use? Example 2: What is the final concentration when 100 mL of water is added to 200 mL of a 12 g/L salt solution? 18 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES Example 3: What volume of water must be added to 500 mL of a 30%V/V hydrogen peroxide solution to dilute it to 6%V/V? Example 4: Using 300 mL of a 45 g/L solution of lithium chloride, LiCl, a student must prepare a 15 g/L solution of lithium chloride. What is the volume of the resulting solution? 2.3 ELECTRICAL CONDUCTIVITY Pure water does not __________________ electricity. How then does it does carry and electric current? It is the substances _____________________ in the water that conducts the electricity. An __________________________ is a substance that when dissolved in water, allows an _____________________ _________________ to flow through the solution. The ELECTRICAL ______________________ of a solution is a measure of its ability to allow ______________________ ____________________ to flow through it. A ________________________________ is a substance that is soluble in water but DOES NOT conduct electricity. 19 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES ELECTROLYTIC DISSOCIATION When an _____________________________ is dissolved in water, it separates into two __________ of opposite charge, one ____________________ and one _______________________. This separation, known as _______________________ _________________________, is a _____________________ change. The chemical equation for the electrolytic dissociation of sodium chloride is: The H2O over the arrow indicates that the change takes place when the _______________ is placed in water. The ions formed during this process _______________________ electricity. A non-electrolyte does not conduct electricity when dissolved in water because it does not _________________________. All covalent compounds (except acids) are non-electrolytes. Here’s what happens when you dissolve methanol (CH3OH) in water: 20 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES THE STRENGTH OF ELECTROLYTES (EST ONLY) To determine whether a solute is an electrolyte: 1. Dissolve it in ___________________ 2. Place two _______________________ in the solution 3. Connect to a power supply and a light bulb 4. Does the bulb light up? Strong Electrolytes Substances that dissociate Weak Electrolytes Substances that only Non-Electrolyte Substances that ________________ ___________________ (100%) ___________________ dissociate produce ions when dissolved in when dissolved in water. when dissolved in water. water. CaCO (s) –>50% → Ca2+(aq) + CO32-(aq) C12H22O11(s) –H2O→ C12H22O11(aq) 100 molecules 100 molecules NaCl –H2O→ Na+(aq) + 100 molecules Cl-(aq) 100 ions + 100 ions 50 ions + 50 ions 100 molecules no light The strength of an _______________________________ is the degree to which it dissociates into ions. The higher the degree of dissociation, the ____________________ the electrolyte. 21 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES TYPES OF ELECTROLYTES Acids Bases Found in fruit juices, ____________ Found in many ______________ ____________, & gastric juices products and in some pH ______________ than 7 _______________________ Taste ________________ medication. Blood and _______ water Turns blue litmus paper ____________ are also slightly basic. Neutralize _________________ pH ________________ than 7 Release H+ ________ when dissolved Taste _______________________ in water Turn _____________ litmus paper blue Molecular formula often begins with Neutralize _________________ the symbol for a _________________ Feel _________________ to the touch atom followed by a nonmetal (HCl, Dissolve _______________ and oils HNO3, HSO4, HF, H2CO3) Release ________________ ions (OH- Acetic acid (aq)) (___________________________) is when dissolved in water Molecular formulas begins with a metal and usually ends in “OH”: the exception to this rule. Examples of acid solutions: NaOH, KOH, NH4OH, Ca(OH)2, 1. Hydrochloric acid: HCl → H+(aq) + Cl-(aq) 2. Nitric acid: HNO3 → H+(aq) + NO3-(aq) 3. Sulfuric acid: H2SO4 → 2H+(aq) + SO42-(aq) Al(OH)3 Exceptions: Alcohols! CH3OH, C2H5OH these are NOT bases and NH3 is a base yet it does not end in OH Examples of basic solutions: 1. 2. 3. Sodium hydroxide: NaOH → Na+(aq) + OH-(aq) Potassium hydroxide: KOH → K+(aq) + OH-(aq) Magnesium hydroxide: Mg(OH)2 → Mg2+(aq) + 2OH-(aq) 22 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES Salts Constitute a ____________ class of substances that figures ________________ in human diets Most are made up of a _______________ and one or more ________________________. pH = _________ (___________________) Have __________ effect on litmus paper A SALT is a substance produced by the ________________ bonding of a ____________________ ion and a ______________________ ion (other than H+ and OH- ions). Examples of salt solutions: 1. 2. 3. 4. sodium chloride: NaCl, potassium bromide: KBr calcium chloride: CaCl2 silver nitrate: AgNO3 Not all salts dissolve easily in water. 2.4 pH Acidic, basic and neutral solutions can be distinguished by their _________. A solutions pH can be measured using a pH _______________________ or a pH _______________. THE pH SCALE ranges from __________ to ____________ if the pH the solution is __________________ if the pH = 7, the solution is _______________________ if the pH the solution is ______________________ the pH scale is ____________________ , which means that a difference of one unit between two substances actually indicates that one of the substances is _________ times more acidic than the other. 23 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES Examples: a) What is the pH of an acetic acid solution that is 100 times more diluted than an acetic acid solution with a pH of 2? ____________________________________________________________________ b) What is the pH of an ammonia solution that is 1000 times more concentrated than an ammonia solution with a pH of 10? ___________________________________________________________________________ Figure 1: The pH of some common substances http://islandwood.org/kids/stream_health/Data/pH_scale.jpg State whether the following substances are acidic, basic, or neutral: Susbtance Acidic, Basic, Neutral? Vinegar Bleach Coke Detergent Sea Water END OF CHAPTER 2 NOTES FOR ST 24 ST 410/EST 404 THE MATERIAL WORLD CHAPTER 2 NOTES MORE ON pH (EST ONLY) The pH of a solution is actually an indication of the concentration of __________________ ions (_____) in that solution. How is pH related to hydrogen ion concentration? pH = -log [H+] where [H+] = hydrogen ion concentration in mol/L So, if the hydrogen ion concentration in a solution is 1 10-3 mol/L, then the pH = _______. Likewise, [H+] = 10-pH So, if the pH of a solution is 8, then the hydrogen ion concentration is _____________________. See Table 2.30 on page 61 of your textbook. THE pOH SCALE The complete opposite of the pH scale, it communicates hydroxide ion concentrations, [OH-], in a wide variety of substances. pOH = -log [OH-] where [OH-] = hydroxide ion concentration in mol/L So if the hydroxide ion concentration in a solution is 1 10-6 mol/L, then the pOH = ________. Likewise, [OH-] = 10-pOH So, if the pOH of a solution is 10, then the hydroxide ion concentration is __________________. How are pH and pOH related? pH + pOH = 14 So if the pH of a solution is 5, then the pOH is ______. END OF CHAPTER 2 NOTES FOR EST 25