Chemistry 140

Chemistry 140Chapter 4: Forces Between ParticlesHCC/TCHSLEARNING OBJECTIVES/ASSESSMENTWhen you have completed your study of this chapter, you should be able to:1. Draw correct Lewis structures for atoms of representative elements.2. Use electronic configurations to determine the number of electrons gained or lost by atoms as they achieve noble gas configurations.3. Use the octet rule to correctly predict the ions formed during the formation of ionic compounds, and write correct formulas for binary ionic compounds containing a representative metal and representative nonmetal.4. Correctly name binary ionic compounds.5. Determine formula weights for ionic compounds. 6. Draw correct Lewis structures for covalent molecules. 7. Draw correct Lewis structures for polyatomic ions. 8. Use VSEPR theory to predict the shapes of molecules and polyatomic ions .9. Use electronegativities to classify covalent bonds of molecules, and determine whether covalent molecules are polar or nonpolar. 10. Write correct formulas for ionic compounds containing representative metals and polyatomic ions, and correctly name binary covalent compounds and compounds containing polyatomic ions.11. Relate melting and boiling points of pure substances to the strength and type of interparticle forces present in the substances. Introduction to Chemical BondingChemical bond a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms togetherWhy are most atoms bonded together?Types of BondsIonic bonding the electrical attraction between large numbers of anions and cationsCovalent bonding the result of sharing electron pairsMetallic bonding the attraction between metal ions and a sea of electronsMolecular bonding bonding between molecules caused by nuclear attraction of outer moleculesNaming Binary Compounds1. First word consists of:a. a prefix to indicate the number of atoms of the first elementb. the name of the first element2. Second word consists of:a. a prefix to indicate the number of atoms of the second element in the formulab. the root name of the second elementc. the suffix ide

Nomenclature Prefixes1 - mono 2 - di 3 - tri4 - tetra 5 - penta 6 - hexa7 - hepta 8 - octa 9 - nona 10 - deca

Name the following compounds.1. CO2_______________________2. CO_______________________3. HBr_______________________4. CCl4_______________________5. As2O5_______________________6. N3O4_______________________7. Na2O2_______________________Naming Other Compoundsfirst word - name of the first speciessecond word - name of the second speciesRoman numerals are used to indicate the oxidation state of transition elements.Name the following compounds.1. CaCO3_______________________2. MgSO4_______________________3. H3PO4_______________________4. CuNO2_______________________5. Fe2(SO4)3_______________________6. Fe2(Cr2O7)3 _______________________7. CuCl_______________________

Name the following compounds. 8. FeF2_______________________ 9. NO3_______________________10. N2O4_______________________11. NH4HSO4_______________________12. NaC2H3O2_______________________13. H2O_______________________14. NH3_______________________

Writing Chemical FormulasChemical formulas are written from names of compounds.The sequence for the formula is the same as the name.The sum of the oxidation numbers of the elements in the formula of a compound must be zero.polyatomic ion - an ion that consists of two or more atoms acting as a single unitParentheses are used to show more than one polyatomic ion.Write formulas for the following.sodium chloride____________magnesium oxide____________calcium chloride____________ammonium sulfide____________aluminum bromide____________copper(II) sulfate____________potassium peroxide____________

Open ResponseWhy is it important to have such a detailed system for naming compounds?Why do atoms share electrons?Hydrogen exists as a molecule and not a single atom? Explain.......The proton in one hydrogen atom attracts the electron in the other and vice versa. What type of force exists between the hydrogen electrons?The electrons repel each other but this repulsive force is far less than the attractive forces.covalent bonding - bonding which results from electron sharingBond PolarityCovalent bonds with uneven electron sharing are polar.Covalent bonds with even electron sharing are nonpolar.electronegativity - the tendency for an atom to attract electrons to itself when bonding with other atomsThe difference between electronegativity can be used to indicate bond type. Bond TypeTo calculate bond type1. Look up the electronegativity of the atoms in question. (chart passed out)2. Find the difference between the electronegativities. (subtract)3. Use the chart to classify the bond asnonpolar covalent (0.0 - 0.4)polar covalent (0.5 1.9)ionic (>2.0)Determine the bond type of each of the following.H2H2ONaClMgCl2Covalent Bonding and Molecular Compoundscovalent bonding - bonding between atoms which results from electron sharingThe particle which results from covalent bonding is a molecule.molecule - two or more atoms bonded covalentlyThere are eight elements in which two atoms bond forming a diatomic molecule. They do not normally exist as single atoms. They are referred to as diatomic elements.diatomic elements - two identical atoms bonded covalentlymolecular compound - a chemical compound whose simplest formula units are moleculesFormulas Represent Compoundschemical formula - a shorthand method of using atomic symbols and subscripts to represent the composition of a substancemolecular formula - a formula indicating the composition of a moleculedot formula - a formula using dot notation to indicate valence electronsformula unit represents the composition of an ionic compound, empirical formulaDIATOMIC ELEMENTS NAMEDOT FORMULA MOLECULAR FORMULAhydrogen H2nitrogen N2oxygen O2fluorine F2chlorine Cl2bromine Br2iodine I2astatine At2Lewis StructuresLewis structures are formulas in which symbols represent nuclei and inner shell electrons and dots, dashes, etc, represent valence electrons.The Lewis structure of water would be similar to the dot formula.Polyatomic IonsA polyatomic ion consists of two or more atoms bonded covalently which has a net charge.Show the Lewis structure for SO4=.Show the Lewis structure for H2 SO4.ExamplesShow the Lewis structures forMgBr2Na2OH3PO4CH3ClAl2S3ResonanceResonance is an attempt to describe bond structure based on data collected about bond length.Example: ozone, O3

Ionic Bonding and Ionic CompoundsIonic bonding results from electron transfer.Ion an atom or group of atoms that has an unbalanced electrostatic chargeCrystal the particle resulting from ionic bondingMost ionic compounds are solids.Salts are examples of ionic compounds.Octet Ruleoctet - a complete outer shell of eight electronsOrbital Notation of argon 1s2s 2p 3s 3pAr __ __ __ __ __ __ __ __ __Show the orbital notation of neon. 1s2s 2pNe __ __ __ __ __

VSEPR TheoryVSEPR - valence shell electron pair repulsion the valence electron pairs repel each other which moves bonded atoms to an equilibrium positionVSEPR accounts for the bent shape of the water molecule.Molecular ShapeA quick indicator of molecular shape is the number of atoms in a molecule. The un-bonded electrons must be taken into account to get the exact shape.What do you think is the shape of:H2H2ONH3CH4Molecular TypeMolecular type is either polar or nonpolar. These are not to be confused with bond type.Polar molecule a molecule which lacks symmetryNonpolar molecule a molecule which has symmetryWhich shapes do you expect to be polar and which do you expect to be nonpolar?Rules for Assigning Oxidation Numbers1. An uncombined element has an oxidation number of zero.2. A monoatomic ion has an oxidation number equal to its charge.3. Fluorine has an oxidation number of -1 in all compounds.4. Oxygen usually has an oxidation number of -25. Hydrogen usually has an oxidation number of +1.6. The more electronegative element in a binary compound is assigned the number equal to the charge it would have if it were an ion.7. The algebraic sum of the oxidation numbers of the elements in a compound is zero.8. The algebraic sum of the oxidation numbers of the elements in a polyatomic ion is equal to its charge. Assign oxidation numbers to each element in the following.1. HClH ___Cl___2. CF4C ___F ___3. PCl3P ___Cl___4. HNO3H ___N ___O ___5. SiO2Si___O ___6. P2O5P ___O ___7. HClO3H ___Cl___O ___

Using Chemical Formulas The formula mass of sucrose, C12H22O11, is equivalent to the molar mass or the mass of one mole of the compound in grams.Element# atoms mass total C 12 x 12 = 144 H 22 x 1 = 22 O 11 x 16 = 176----------------------------------------------------- formula mass.....342g/molDetermine the molar mass of each of the following.1. HNO32. Fe2(SO4)33. calcium hydroxide4. barium nitrate5. CuSO4.5H2OMoles of CompoundsOne mole of a compound contains ? molecules or formula units?The molar mass expressed in grams is the mass of one mole of a compound, Avagadros number of formula units or molecules.Find the mass of 0.25 moles of calcium carbonate.How many moles in 1Kg of magnesium sulfate?

Percentage CompositionPercent can be found by using the formula part % = -------------X 100 wholeSample ProblemFind the percent of oxygen in water.1. Write the formula for water. H2O2. Find the formula mass of water.element #atoms mass totalH21 2O1 16 16 ----- 18g/molSample Problem Continued3. Calculate % O. % = (part/whole) X 100%O = (16/18) X 100%O = 1600/18%O = 88.89%What would be the percent H in water?Find the percentage composition of sodium hydroxide.1. Write the formula for sodium hydroxide.2. Find the formula mass.3. Percentage composition refers to the percent by mass for each element in the formula of the compound. Find the percent Na, O, and H.Calculation of Chemical Formulas from Percentage Composition1. Assume a 100g sample and express percentages as mass in grams.2. From the mass data, determine the number of moles of each element present.3. Write a mole ratio formula.4. Determine the atom ratio by dividing each mole number by the smallest number and rounding off when appropriate. (Only round 0.1s and .9s. If these are not present, multiply through by integers until they are present.) Finding Chemical FormulasThe analysis of a compound determined a percentage composition of 80% carbon and 20% hydrogen. Find the formula.Sample Problems1. Does smithsonite, ZnCO3, or sphalerite, ZnS, have more zinc per gram of sample?2. The mineral greenockite is a rare yellow sulfide of cadmium that is 78% cadmium and 22% sulfur by mass. What is the empirical formula of this compound?3. What is the formula for a compound of aluminum and fluorine that is 32% Al and 68%F?Determination of the Molecular Formula1. Determine the empirical formula.2. Determine the empirical formula mass.3. Use the following formula to determine the multiple, x, of the empirical formula.(empirical formula mass) x = molar mass4. Multiply the empirical formula subscripts by the multiple x to determine the molecular formula.A compound has an empirical formula HO. The molar mass of the compound is 34g/mol. Find the molecular formula.1. Empirical formula = HO.2. Empirical formula mass = 1 + 16 = 17g/mol.3. Determine multiple x.17x = 34 x = 34/17 x = 24. Determine molecular formula(HO)2 = H2O2Sample ProblemThe analysis of a compound determined a percentage composition of 80% carbon and 20% hydrogen. The molar mass was determined to be 45 g/mol. Find the molecular formula.Answer: C3H9