Presentation on theme: "Writing Chemical Formulas and Naming Chemical Compounds"— Presentation transcript:
1 Writing Chemical Formulas and Naming Chemical Compounds Part 1: Writing Chemical Compounds
2 Chemical Formulashort hand method of indicating a ratio of atoms in a compound.identifies the atoms in a compoundthe less electronegative element is listed first in the formulafor covalent compounds, the formula tells you how many atoms of each type in the molecule.
4 Valence or Oxidation Numbers describes how many electrons from an atom are used in bond formationif its an ionic bondindicates how many electrons are donated ( + )indicates how many electrons are received ( - )if it’s a covalent bond it indicates how many electrons are contributed to the bond as if the electrons were completely removed or gained.
5 Oxidation NumbersAn oxidation number is the charge an atom would have if the electron pair that is shared between two atoms belonged entirely to the more electronegative atom.
6 Rules for Oxidation Numbers The following rules will help to assign oxidation numbers. The rules are listed in PrioritySequence.free atoms (0) Ex. Al(s)atoms bound to eachother. (0) Ex. Cl2, Hmonoatomic ions have the same oxidation number as the charge numberEx. Cl1- (-1), Mg2+ (+2),F is always (-1)O is almost always (-2) -except in peroxidesH is almost always (+1) -except for metallic hydridesAssign oxidation numbers to the most electronegative atom first
7 Rules ContinuedGroup I (+1) Group II (+2) Al (+3) Group VII (-1) Group VI (-2) When forming binary compounds with metals. Group V (-3) nonmetals only In general, if two atoms form an ionic bond, the valence tells you the charges on the ions that are formed. If a covalent bond is formed, the valence tells you how many electrons the atoms contribute to the covalent bond.
9 Writing Chemical Formulas Using Valences Use the Zero Sum Rule (for neutral compounds only)algebraic sum of oxidation numbers is zerofor charged polyatomic ions, the sum of oxidation numbers equals the charge of the ion.Example: KFEach potassium ion has a charge of +1 and each fluorine ion has a charge of -1. Because there is one of each ion in the formula, the sum of the valences is zero.
10 Polyatomic Ions ions made of more than two atoms are charged molecules very strong covalent bonds keep these ions together and react as a single inseparable ion.
11 Need to Memorize...Ammonium NH4+ Acetate C2H3O2- Hydroxide OH- Nitrate NO3- Carbonate CO32-Chlorate ClO3- Sulfate SO42- Phosphate PO43- Cyanide CN-
15 Writing Chemical Formulas and Naming Chemical Compounds Part 2: Naming Chemical Compounds
16 Chemical Nomenclature Each chemical compound has been given a name. Some have a trivial or common name, H2O is known as water.These names have been used for centuries. However all chemicals have been given a name using Systematic Nomenclature.uniquely describes it s compoundthe name is derived from its chemical formulafrom a name a formula can be determinedex. NaCl common name: salt; (sodium chloride) H2O common name: water (hydrogen oxide)
17 Positive Monoatomic Ions the name of the positive monoatomic ion is the same as the element nameEx. Li+ -lithium Stock System:if the metal has more than one oxidation number, a Roman Numeral is used: Sn2+ -Tin(II)Sn4+ Tin(IV)Old Method:the old name along with the suffix -ous or -ic is used to indicate the oxidation number.Sn2+ -stannousSn stannicMemory Aid: -ous -indicates the lower oxidation number-ic -indicates the higher oxidation number
18 Negative Monoatomic Ions add -ide to the end of the element name.Ex. chlorine (Cl) becomes chloride (Cl- )
19 Binary Compounds Containing a Metal and a Nonmetal consist of only 2 different elementsthe element with the more positive oxidation number is written first.Ex. NaCl and not ClNa
20 Binary Compounds Containing Hydrogen and Another Element compounds of hydrogen and nonmetals from group VI and VII are called:hydrogen _______ideex. HBr is call hydrogen bromidecompounds of hydrogen and a metal, the metal is written first and are called:________________ hydrideex. NaH is called sodium hydride
21 Binary Compounds Containing 2 Nonmetals this method uses prefixes to indicate the number of nonmetal elements present__________name _______nameex. As2S3 is called diarsenic trisulfideNO is called nitrogen monoxideN2O5 is called dinitrogen pentoxide
22 Naming Chemical Compounds Containing More than Two Elements Polyatomic ion + nonmetal ionname the positive portion first then the negative ionnegative monoatonic ions end in –ideex. NH4Cl is called ammonium chlorideCation + polyatomic ionoxygen containing polyatomic ions end in either –ate or –ite.an –ite polyatomic ion contains one less oxygen than does an-ate polyatomic ion.(Memory aide: memorize the –ate form of ions)ex. SO42- is sulfate and . SO32- is sulfite
23 Group VII Polyatomic Ions have Additional Forms ClO- hypochloriteClO2- chloriteClO3- chlorateClO4- perchlorate
24 Nomenclature of AcidsAcid molecules contain hydrogen atoms that are easily removed when dissolved in water. These ionizable hydrogen atoms appear at the beginning of the chemical formula.Binary Acidshydrogen and a nonmetal element from group VI or VII is called:hydrogen ______ide.when this compound is dissolved in water, it becomes an acid called:hydro________ic acidex. HCl (g) + H2O (l) → HCl (aq)hydrogen chloride hydrochloric acid
25 Oxyacids hydrogen and a negative polyatomic ion is called: hydrogen polyatomic ionex. H2SO4 (g) hydrogen sulfateH2SO3 (g) hydrogen sulfitewhen these compounds are dissolved in water are called:ex. H2SO4 (aq) sulfuric acidH2SO3 (aq) sulfurous acidNote: In acid form –ate polyatomic ions become -ic acid-ite polyatomic ions become -ous acid
27 Proof for existence of intermolecular forces ON COOLING AND COMPRESSINGGases have large distances between their particles, so short range forces between molecules are insignificant.ON further COOLING AND COMPRESSINGSo gases liquefy. So (GL) i.e. LiquefyThese weak forces become significant as the distances are reduced and their magnitude can now make a difference.So (LS ) i.e. solidifiesForces become more significant and hence the liquid solidifies.The distances are further reduced.
28 Types of Intermolecular forces Van der waals’ forcesArise due to random movement of electrons leading to the formation of instantaneous dipole and hence induced dipoles in moleculesTheir strength depends upon the molar mass of the molecule.These forces are effective over a short range.They are dependent on the surface area of the moleculeDipole-dipole forcesThese occur due to electrostatic attraction between molecules with permanent dipoles.They are significantly stronger than van der waals’ forces in molecules of a similar size.Molecule will have not just VVF but in addition to them the DPDP forces also.Hydrogen bondingThis occurs in molecules that contain H bonded to N/O/FThe non bonding e- pair on these N/O/F atoms interacts with the H atom that carries a high δ+ character coz its bonded to another of these small very electro- atoms.It’s the strongest of all the intermolecular forces.
29 Examples to explain Van der waals’ forces Boiling points of noble gasesHe – 4KXe – 165 KMore atomic mass hence more no. of electronsBoiling points of AlkanesMethane111 KHexane 341 KAs molar mass increases the VVF also increaseBoiling points of HalogensAs molar mass of halogens increases from F2 to I2 the boiling points also increaseBoiling points of straight chain & branched Alkanes of same molar massn pentane BP 309 Kneo pentane BP 283 KMolar mass and very high surface areaPlastics and polymersThey have very high
30 Examples to explain dipole-dipole forces Hδ+— Clδ- ||||||||||||Hδ+— Clδ electrostatic attractionThe HCl molecule is polar and has slight negative and slight positive centres on it.This is a permanent DIPOLE and it interacts with other dipoles also and this electrostatic attraction will be DP-DP forces.Comparing the boiling points of non polar noble gases and polar hydrogen halides of same molar massesBoiling points of Non-polar Ar, Kr and Xe will be lower than those of Polar hydrogen halides like HCl, HBr and HIBecause these are permanent dipoles they will have DP-DP forces along with VV forces
31 Hydrogen bonding Hδ+— Fδ- ---------------Hδ+— Fδ- hydrogen bond Considerably stronger than other intermolecular forces.Affects the physical properties of the compounds in which it exists.
32 Examples of H-Bonding Propane C3H8 only VVF BP is 231 K Comparing BP of Hydrogen peroxide, Fluorine and Hydrogen Chloride (Mr ~ 34-36)Hydrogen peroxide 431 K (polar, hydrogen bonded)Hydrogen Chloride 188 K (polar)Fluorine 85 K (non polar)Comparing BP of Propane, Ethanal and Ethanol (Mr~ 44-46)Propane C3H only VVF BP is 231 KEthanal CH3CO-H VVF, polar BP is 294 KEthanol CH3CH2OH VVF, polar, Intermolecular H bonding—352 K
34 Collision TheoryA reaction will only be successful if it has the correct orientation and energy. Baseball Model: Baseball bat is Reactant A, baseball is Reactant B. The reaction is successful if the batter hits a homerun!
35 The scenarios… Pitcher throws a fast ball, batter swings and misses. Pitcher throws off-speed and the batter just makes contact with the ball. It’s a foul.Pitcher throws a curve ball, batter swings and just hits the ball sending it to right field.Pitcher throws a fast ball, batter swings and the ball goes flying high in the air. HOMERUN!When did the reaction occur?
36 Try with moleculesReaction: H2 + I2 2 HI + H2 I2 HI How would you orient the molecules to get an effective collision capable of producing two hydrogen iodide molecules?
37 Types of ReactionsThere are five types of chemical reactions we will talk about:Synthesis reactionsDecomposition reactionsSingle displacement reactionsDouble Displacement reactionsCombustion reactionsYou need to be able to identify the type of reaction and predict the product(s)
38 Steps to Writing Reactions Some steps for doing reactionsIdentify the type of reactionPredict the product(s) using the type of reaction as a modelBalance itDon’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O2 as an element.In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!
39 1. Synthesis reactionsSynthesis reactions occur when two substances (generally elements) combine and form a compound. (Sometimes these are called combination or addition reactions.)reactant + reactant 1 productBasically: A + B ABExample: 2H2 + O2 2H2OExample: C + O2 CO2
40 PracticePredict the products. Write and balance the following synthesis reaction equations.Sodium metal reacts with chlorine gas2 Na(s) + Cl2(g) 2 NaCl (s)Solid Magnesium reacts with fluorine gasMg(s) + F2(g) MgF2 (s)Aluminum metal reacts with fluorine gas2 Al(s) F2(g) 2 AlF3 (s)
41 2. Decomposition Reactions Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds1 Reactant Product + ProductIn general: AB A + BExample: 2 H2O 2H2 + O2Example: 2 HgO 2Hg + O2
42 Decomposition Exceptions Carbonates and chlorates are special case decomposition reactions that do not go to the elements.Carbonates (CO32-) decompose to carbon dioxide and a metal oxideExample: CaCO3 CO2 + CaOChlorates (ClO3-) decompose to oxygen gas and a metal chlorideExample: 2 Al(ClO3)3 2 AlCl3 + 9 O2There are other special cases, but we will not explore those in Chemistry 11
43 PracticePredict the products. Then, write and balance the following decomposition reaction equations:Solid Lead (IV) oxide decomposes PbO2(s) Pb (s) + O2 (g)Aluminum nitride decomposes2 AlN(s) 2 Al (s) + N2(g)
44 PracticeIdentify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation:N2(g) + O2(g) BaCO3(s) Co(s)+ S(s) NH3(g) + H2CO3(aq) NI3(s) Nitrogen monoxide(make Co be +3)
45 3. Single Displacement Reactions Single Displacement Reactions occur when one element replaces another in a compound.A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-).element + compound product + productA + BC AC + B (if A is a metal) ORA + BC BA + C (if A is a nonmetal)(remember the cation always goes first!)When H2O splits into ions, it splits intoH+ and OH- (not H+ and O-2 !!)
46 Single Replacement Reactions Write and balance the following single replacement reaction equation:Zinc metal reacts with aqueous hydrochloric acidZn(s) HCl(aq) ZnCl2 + H2(g)Note: Zinc replaces the hydrogen ion in the reaction2
47 Single Replacement Reactions Sodium chloride solid reacts with fluorine gasNaCl(s) + F2(g) NaF(s) + Cl2(g)Note that fluorine replaces chlorine in the compoundAluminum metal reacts with aqueous copper (II) nitrateAl(s)+ Cu(NO3)2(aq)
48 4. Double Replacement Reactions Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compoundCompound + compound product + productAB + CD AD + CB
49 Double Replacement Reactions Think about it like “foil”ing in algebra, first and last ions go together + inside ions go togetherExample:AgNO3(aq) + NaCl(s) AgCl(s) + NaNO3(aq)Another example:K2SO4(aq) + Ba(NO3)2(aq) KNO3(aq) + BaSO4(s)
51 5. Combustion ReactionsCombustion reactions occur when a hydrocarbon reacts with oxygen gas.This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: 1) A Fuel (hydrocarbon) 2) Oxygen to burn it with 3) Something to ignite the reaction (spark)
52 Combustion Reactions In general: CxHy + O2 CO2 + H2O Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide)Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)
53 Combustion ReactionsEdgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.
54 CombustionExampleC5H O2 CO2 + H2OWrite the products and balance the following combustion reaction:C10H O2 856
55 Mixed PracticeState the type, predict the products, and balance the following reactions:BaCl2 + H2SO4 C6H12 + O2 Zn + CuSO4 Cs + Br2 FeCO3
56 Total Ionic EquationsOnce you write the molecular equation (synthesis, decomposition, etc.), you should check for reactants and products that are soluble or insoluble.We usually assume the reaction is in waterWe can use a solubility table to tell us what compounds dissolve in water.If the compound is soluble (does dissolve in water), then splits the compound into its component ionsIf the compound is insoluble (does NOT dissolve in water), then it remains as a compound
58 Solubilities Not on the Table! Gases only slightly dissolve in waterStrong acids and bases dissolve in waterHydrochloric, Hydrobromic, Hydroiodic, Nitric, Sulfuric, Perchloric AcidsGroup I hydroxides (should be on your chart anyway)Water slightly dissolves in water! (H+ and OH-)For the homework… SrSO4 is insoluble; BeI2 and the products are solubleThere are other tables and rules that cover more compounds than your table!
60 Net Ionic EquationsThese are the same as total ionic equations, but you should cancel out ions that appear on BOTH sides of the equationTotal Ionic Equation:2 K+ + CrO Pb NO3- PbCrO4 (s) + 2 K+ + 2 NO3-Net Ionic Equation:CrO Pb+2 PbCrO4 (s)
61 Net Ionic EquationsTry this one! Write the molecular, total ionic, and net ionic equations for this reaction: Silver nitrate reacts with Lead (II) Chloride in hot water.Molecular:Total Ionic:Net Ionic: