ANSWER KEY M-9 A “CLOSER” LOOK AT THE STRUCTURE OF MATTER How do scientists predict, illustrate, and show chemical bonding? How do atoms “get together” (i.e. bond)? An Intro to Structural Formulas and Bonding – Notes and Review DO NOW: Do you remember where bonding occurs in an atom? Do you remember why bonding must occur between atoms? Do you remember the three ways that atoms can “get together” (i.e. bond!)? If you remember SOMETHING from yesterday’s quickie intro lecture on bonding OR any of the lectures before break…write it in the space below…even if it is only one idea or word or concept! Just get those brain cell juices flowing and try to remember what we’ve discussed so far about BONDING…it will help you get ready for our Intro to CHEMICAL EQUATIONS, STRUCTURAL FORMULAS, and BONDING discussion! 1) Why must bonding occur between atoms? __to create molecules, compounds, higher forms of matter.____ 2) Where does bonding occur in an atom? _____between the valence shell of atoms___________________ 3) What are the three ways that atoms can bond? ____share, lose, gain electrons_______________________ INTRODUCTION: The overview of the “Why, Where, and What” of bonding It is important that atoms bond. Why? Because they need to bond in order to make _molecules______, ___compounds__, and other more complex forms of matter. For example, if atoms didn’t bond, you would be quite thirsty all the time! Yes, __WATER___ is the result of the process of CHEMICAL bonding. To make this compound, _hydrogen__ and ___oxygen_____ must be ___chemically__ bonded together. WARNING: when this is done, you can make quite an explosion, believe it or not! Bonding occurs between the ___valence_____ shells of atoms. It is here that electrons are __shared__, ___lost ___, or ___gained__. When atoms __share_____, ___lose___, or __gain___ electrons, they are no longer neutral and are now called __ions___. The _ions___are attracted to one another due to the __electromagnetic___ force and a bond forms to make a __molecule_______ . Keep in mind that bonding is the result of a __chemical____reaction – NOT a physical mixing of the atoms! OVERVIEW: How do you make water? A Look at the Making of a Molecule Recipe for H20 (Yield: 2 molecules) Step 1. Gather your base ingredients (elements/atoms) by looking at the MOLECULAR FORMULA. Hydrogen = H Oxygen = O Step 2. Find the number of valence electrons and valence # of each of your ingredients (elements/atoms). Column # on Periodic Table Element/Atom # of Valence e- Valence # Hydrogen (H) 1 1 -1 Oxygen (O) 6 6 +2 Step 3. Predict using ELECTRON DOT DIAGRAMS (Lewis Structures). Step 4. Analyze what each ingredient (element/atom) needs to be “happy.” REMEMBER: electrons are lost, gained or shared in bonding! Hydrogen needs one electron or needs to lose one electron. Oxygen needs to gain two electrons. Step 5. Gather all necessary ingredients (elements/atoms)! Since O needs two electrons, it needs two H’s (each H has 1 electron to donate/share) Step 6. Bond your ingredients (elements/atoms) using the ELECTRON DOT DIAGRAMS; fill in the missing spaces to create “happiness” for all ingredients. Step 7. Turn your bonded Electron dot diagrams into STRUCTURAL FORMULAS. Step 8. Analyze the TYPE OF BOND made. Ionic – Lose and Gain Covalent – Share Metallic – Lose electrons and float around positive centers Water is made up of COVALENT bonds…polar covalent in fact! Oxygen has more of an affinity for the electrons than hydrogen does. Step 9. Write out the CHEMICAL EQUATION. Be aware of DIATOMIC ELEMENTS! (H2 I2 Br2O2 N2 Cl2 F2) H2 + O2 H2O Step 10. Use COEFFICIENTS to balance your equation. 2H2 + 1O2 2H2O Step 11. Wait for the “BOOM” and then enjoy your tasty treat. Yield: 2 molecules of H20 PART I: How do scientists predict, illustrate, and show the chemical reaction that occurs when atoms bond? Scientists may use _Bohr___ MODELS or __Electron_____ DOT DIAGRAMS (a.k.a. LEWIS STRUCTURES) to predict bonding between atoms. Scientist show how atoms bond by writing _chemical __equations__ and _structural__ _formulas__. For chemical equations: Molecular formulas consisting of the correct combination and number of atoms are used to represent the molecules and/or atoms that are being bonded. (e.g. H2O is the molecular formula for water!) An “ ” is used to show what substance(s) is/are being “yielded” or chemically produced. Atoms on the LEFT side of the arrow are referred to as REACTANTS and the atoms on the RIGHT side of the arrow are referred to as PRODUCTS. And, most importantly, the equation is BALANCED…just like in algebraic math! To do this, a number is placed before the molecular formulas to balance the amount of atoms on each side of the equation --- this number is called a COEFFICIENT. FYI…the number below and to the right of each chemical symbol is called a SUBSCRIPT. 2H2O Coefficient Subscript Chemical equation examples: H20 (water) 1) 2H2 + 02 2H20 (DIATOMIC!!!!!) CH4 (methane) 2) C + 4H CH4 For structural formulas: An electron dot diagram or Lewis structure is created for atoms involved in the chemical bonding process. A chemical symbol is used to represent the atoms that are being bonded. The appropriate number of dots is drawn on the four sides of the chemical symbol to represent the number of valence electrons and “empty spots” in the valence shell of the bonding atoms. Structural formulas are used to represent what the atoms look like when they are “brought together” in the chemical bond. To show this, the electron dot diagrams for each atom are drawn and puzzle-pieced together by filling their “empty spots” with each other’s valence electrons. In the final structural formula, ALL dots are removed from the electron dot diagram and “bonded” electrons are replaced with lines. Here are the structural formulas of some common compounds and molecules: Molecule Name Molecular Formula Carbon dioxide CO2 Ammonia Vinegar Sucrose Structrual Formula O—C—O H–N–H NH3 H CH3COOH C12H22O11 (table sugar) Electron Dot Diagram and Structural Formula Examples: Molecular Electron Dot Diagram for First Atom Formula H20 (water) CH4 (methane) Electron Dot Diagram for Second Atom Structural Formula Because the Periodic Table is set up in a periodic, predictable way, we can predict what the Electron Dot diagrams (a.k.a. Lewis Structures) look like for each of the 8 major columns of the Periodic Table. Column Number of Valence Electrons Valence Number Example Element 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 -1 -2 -3 + or – 4 +3 +2 +1 0 Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Metal Metal Nonmetal Nonmetal Nonmetal Inert or Noble Gas Family Metalliod Nonmetal Lewis Structure (Electron Dot Diagram) IMPORTANT: Imagine a box around the element symbol. X Place the FIRST DOT on the right side. next to the first dot. X Place the SECOND DOT next to the first dot. X Place the remaining dots in a counterclockwise fashion…putting a maximum of two dots on each side of the imaginary box around the element X X X X X PART II: How do atoms “get together” (i.e. bond)? THE 7 SIMPLE RULES OF BONDING: RULE #1 – All atoms want to be “happy.” “HAPPY” means that their __valence___ __shell_ is filled to the _maximum__ capacity ( _2_ electrons for the first level and _8_ electrons for all other levels). ONLY the _inert____ or __noble____ gases are “happy” because they already have the __maximum__ amount of electrons in their __valence______ shell. HAPPY NOT HAPPY RULE #2 – To be “happy,” atoms will bond with one another. They will either _lose_____, __gain________, or ____share________ their __valence___e-! RULE #3 Atoms will bond with each other ONLY if they can both be “__happy__” (i.e. have __full/complete______ valence shells) when they “get together” or bond __chemically_______! HAPPY NOT HAPPY RULE #4 - Atoms will do what is “easiest” --- that is, they will bond in a way that requires them to use the LEAST amount of energy. MAKING BONDS REQUIRES ENERGY! Atoms with a valence that is LESS than _four_______ will __lose____ their electrons. Atoms with a valence that is MORE than _four______ will __gain_____ electrons from another atom. Remember: it is BEST to “GAIN _MORE____ and LOSE___LESS__!” eg. Na – Valence e- = _1___ _____Lose 1e-________ RULE # 5 – Elements that have exactly _4___ electrons in their __valence____ shell will EITHER _lose__ OR __gain___ electrons. These elements are located in column __4____! These elements are called (ha-choo…extra credit…ah-hem) __amphoteric____________. This means that they can “go both ways” --- i.e. __lose__ or __gain___ electrons depending upon what the OTHER atom they are bonding with wants to do! RULE #6 – By drawing the _Bohr_ model or SIMPLY looking at the __valence_______ #’s on the periodic chart, you can figure out the number of __valence__ electrons that an atom has and, thus, what it needs to do to be “_happy___.” Remember Mendeleev and his periodic pattern of VALENCE NUMBERS? The top of the major columns can be labeled to reflect the number of electrons in the valence shell or the number of electrons the atoms will _lose___ or __gain____ to become happy! Label the diagram below! The Periodic Table of the Elements Less than four = __LOSE_____ More than four = __GAIN___ (# of valence e-) _1_ _2_ _3_ _4_ _5_ _6_ _7_ _8_ (valence #) _-1 _-2 _-3_ +/-4 +3 _+2_ +1 _0_ __Lose__ or __Gain__ RULE #7 – The families of the periodic chart have a tendency to be “losers” or “gainers”. Most __metals___, because most of them have less than four electrons want to be __losers____. Most __non-metals__, because they have more than four valence electrons want to be __gainers________. Noble or inert gases do __NOT_____ want to _lose_____ or _gain______ ANY electrons…they are already happy (i.e. _stable_____!). THE TYPES OF BONDS: BOND TYPE and NICKNAME DESCRIPTION BONDING FAMILIES EXAMPLE Metals and non-metals Sodium and Chlorine to make NaCl (table salt). Sodium loses one e- and chlorine gains one e- Non-metals w/ nonmetals Hydrogen w/ oxygen to make Water. Hydrogen wants to gain one and water wants to gain two. Aluminum with Aluminum. One atom _loses___ electrons and IONIC give a little, take a little COVALENT sharin’ to make a pairin’ the other _gains__electrons. Atoms _share_________ their electrons. Metals w/ metals The electrons of the atoms METALLIC lost at sea “_float__” in a “sea” around the positive nuclei of the atoms. See here for example molecular structures: http://www.chemcool.com/regents/chemicalbonding/aim5.htm PART III. PUTTING IT ALL TOGETHER…Chemical equations, Structural Formulas, and Bonding Rules Use your new bonding knowledge to figure out what types of bonds the following atom pairs would most likely make! Fill in the family names, the # of electrons in their valence shell, their valence number (i.e. how many e- they want to lose, gain, or share to be “happy”), the resulting bond name, and structural formula. Then write the BALANCED chemical equation for the chemical reaction between the two atoms. DO NOT FORGET TO USE YOUR PERIODIC CHART! EXAMPLE 1. ATOM Family NAME Na Metal (Sodium) Cl Non-Metal (Chlorine) # of valence e1 7 Valence # Electron Dot Diagram RESULTING BOND STRUCTURAL FORMULA Ionic Na-Cl -1 +1 Chemical Equation: ______Na + Cl NaCl________________________________________ EXAMPLE 2. ATOM Family NAME Al Metal (Aluminum) Al Metal (Aluminum) # of valence e3 Valence # 3 -3 Electron Dot Diagram -3 RESULTING BOND Metallic STRUCTURAL FORMULA Al-Al Chemical Equation: ______Al + Al Al2_______________________________________ EXAMPLE 3. ATOM Family NAME C (Carbon) Non-metal # of valence e4 Valence # Electron Dot Diagram + or – 4 RESULTING BOND Covalent STRUCTURAL FORMULA O=C=O O (Oxygen) Non- metal 6 +2 Chemical Equation: _______C + 20 CO2______________________________________ EXAMPLE 4. ATOM Family NAME K Metal (Potassium) Br Non-metal (Bromine) # of valence e1 Valence # -1 Electron Dot Diagram RESULTING BOND Ionic STRUCTURAL FORMULA K-Br 7 +1 Chemical Equation: _______K + Br KBr______________________________________ PART I. CHEMICAL EQUATIONS AND STRUCTURAL FORMULAS A. Fill in the missing information in the following chemical equations. You may need to fill in a symbol and/or a coefficient to make each equation correctly written and balanced. 1. When heated, aluminum reacts with solid copper oxide to produce copper metal and aluminum oxide. Products Reactants 2Al + __3__CuO ____________ Al2O3 + _3___Cu 2. Potassium Oxide is not a stable compound and, in the presence of water, it changes into potassium hydroxide. Products Reactants K2O + H2O __2___KOH Here are some more practice problems… Products 3. Reactants 2NaCl + BeF2 4. _2_NaF + BeCl2 _1_AgNO3 + _1_LiOH 5. CH4 + _2_O2 6. _3_Mg + _1_Mn2O3 _1_AgOH + _1_LiNO3 CO2 + 2H2O _3_MgO + _2_Mn B. Draw the electron dot diagrams (a.k.a. Lewis Structures) for the following atoms. 1. F 2. Ne 3. B 4. Mg C. In the boxes draw the structural formulas for the following molecules by rewriting the electron dot diagrams given. 1. H Cl 2. Mg O 3. F Be F PART II. BONDING RULES Match the term with the definition. DEFINITIONS TERMS __a_ 1. The element family that usually LOSES electrons. a) Metals __f_ 2. The bond that occurs between non-metals. b) non-metals _d__ 3. The bond that occurs when one atom loses electrons and the other gains electrons. c) inert gases __b_ 4. The element family that usually GAINS electrons. d) ionic bond __c_ 5. The element family that usually does NOT bond easily with other elements. e) metallic bond __g_ 6. The group of elements that can either lose or gain electrons. f) covalent bond __e_ 7. The bond that occurs between metals. g) amphoteric __e_ 8. The bond in which electrons “float” around the positive nuclei of the bonding atoms. _f__ 9. The bond in which atoms share their valence electrons. __d_ 10. The bond that occurs between non-metals and metals.