Formula Writing and Equation PDF

WRITING CHEMICAL Chapter 5: Molecules and FORMULAS AND EQUATIONS Compounds LEARNING GOALS/ OBJECTIVES Review monoatomic and polyatomic radical table and formula writing Understand the parts of a chemical equation Understand the types of chemical equations Convert word equations to ch...

WRITING CHEMICAL Chapter 5: Molecules and FORMULAS AND EQUATIONS Compounds LEARNING GOALS/ OBJECTIVES Review monoatomic and polyatomic radical table and formula writing Understand the parts of a chemical equation Understand the types of chemical equations Convert word equations to chemical equations Convert chemical equations to word equations Balance chemical equations Memorize solubility rules Write ionic/ precipitation reactions Balance ionic reactions Define, identify and delete spectator ions Write net ionic reactions REMEMBER THESE A compound is a substance formed when two or more chemical elements are chemically bonded together.... Example 1: Pure water is a compound made from two elements - hydrogen and oxygen. An element is a substance whose atoms all have the same number of protons: another way of saying this is that all of a particular element's atoms have the same atomic number. An atom is the smallest unit of matter that has the properties of an element. It is composed of a dense core called the nucleus and a series of outer shells occupied by orbiting electrons. A valence shell is the last shell of atom. It houses an electron that can be transferred to or shared with another atom. DEFINITION OF CHEMICAL FORMULA A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses(brackets), dashes, dots,and plus (+) and minus (−) signs. Dot represents an weak bond formed by water to the compound. This is called water of crystallization. If heat is applied this bond can break and water is released as moisture/ steam. WRITING FORMULAS FOR IONIC COMPOUNDS Ionic compounds always contain positive and negative ions. These are a metal cation and a non metal anion. It has to have these. In the chemical formula, the sum of the charges of the cations must always equal the sum of the charges of the anions. STEPS FOR WRITING FORMULAS FOR IONIC COMPOUNDS/ FORMULA UNITS Step 1. Write the symbol for the metal and its charge first followed by the symbol of the nonmetal and its charge. Eg. We are bonding aluminum and oxygen. WRITING FORMULAS Step 2. Make the magnitude of the charge on each ion (without the sign) become the subscript for the other ion. In summary SWITCH THE CHARGES an write formula Al 3 O 2- + Al2O3 2,8,3 2,6 WRITING FORMULAS 3. BRACKET IF YOU HAVE A POLYATOMIC ANION or CATION AND YOU ARE SENDING DOWN A CHARGE OF MORE THAN 1+ OR 1- 4. If possible, reduce the subscripts to give a ratio with the smallest whole numbers and if the subscripts are the same cancel them. 5. Check to make sure that the sum of the charges of the cations exactly cancels the sum of the charges of the anions. Al2O3 NAMING IONIC COMPOUNDS When writing ionic formulas the formula name consists of the name of the two ions. The name of the metal cation comes first and the name of the anion( non metal ion) comes second but the last part of the name of the anion is changed to “ide USE OF SUFFIX IN NAMES OF IONIC COMPOUNDS Suffix Bi- Hydrogen is present in the compound Sodium bicarbonate (NaHCO3) -ide There are only 2 types of atoms present in Lead oxide (PbO) the molecule. and carbon dioxide (CO2) -ate There are 3 or more types of atoms in the Calcium carbonate compound, and 1 type is oxygen (CaCO3) NB. the names of both cation radical and anion radical takes the name of both radical in many cases. Yet there are special cases RULES CONTINUED Switch the charges. If you have a monovalent, divalent, or trivalent cation or anion bonding to a polyatomic anion or cation you must bracket the polyatomic anion or cation when switching charges if one ion in the formula has more than a +1 charge Cancel out charges if both charges are the same numerically. If they are not the same leave them. Do not write back the charge symbol Write the name of the formula LETS PRACTICE WITH SOME CATIONS AND ANIONS FROM THE TABLE Write the formulas and names for ionic compounds that form from the following:  Mg and O  F and Li  Ca and Cl  N and K  S and Al  Iron (II) and Phosphate  Zinc and Nitrogen  Ammonium and Dichromate WRITING FORMULAS WITH POLYATOMIC ANION AND CATION Recognize polyatomic ions in a chemical formula by becoming familiar with these common polyatomic ions. Just as we did with monoatomic ions, make sure that the charges cancel out. PRACTICE Write the formula and name for the compound that forms from calcium and nitrate ions. PRACTICE Write the formulae for ionic compounds that form from the following:  aluminum and phosphate  Sodium and carbonate  Calcium and carbonate  Aluminum carbonate  sulfite and sodium  Calcium and phosphate  Convert the following formula to words( give their names)  K2 O  CH3COONa  Li2CO3  Zn3(PO4)2  Na3PO4  MgCl2 WRITING THE FORMULAS OF COVALENT MOLECULES what is a covalent compound? It is called a molecule and it only has two or more non metal atoms sharing electrons with each other. Important--carbon only forms covalent bonds. It can form 4 covalent bonds as it is tetravalent. What is the difference between an ionic compound and a covalent molecule- Note that hydrogen can be a cation if bonded to non- metal and a anion if bonded to metals. The formula of a covalent compound gives the exact number of atoms of each element in one molecule of the compound i.e its molecular formula. Moreover it is not necessary to know valences as the name will give the number of atoms by using a prefix.  THE PREFIX TABLE ON THE BOARD In naming a binary(binary compound is a substance composed of exactly two different elements, which are substances that cannot be simplified further by chemical means) molecular compound, the number of atoms of each element present in the molecule is noted by using prefixes. When NamingPrefixthem Number of atoms Example Mono 1 atom of that type of element in the Carbon Monoxide (CO) molecule Di 2 atom of that type of element in the Carbon dioxide(CO2) molecule Diphosphorous mono chloride ( P2Cl) Tri 3 atom of that type of element in the Carbon trioxide(CO3) molecule Tetr or tetra 4 atom of that type of element in the Carbon Use of suffix molecule tetrachloride( CCl4 ) -ide Tells us that There are carbon dioxide (CO2) only 2 types of atoms Pent 5 atom of that type of element in the Vanadium present in the molecule pentoxide( V2O5) molecule Hexa 6 atom of that type of element in the molecule 7 hepta- Octa 8 9 nona 10 Deca The previous table will be used to explain the formation of the following compounds CO is the formula for carbon monoxide SO2 is the formula for sulphur dioxide SO3 is the formula for sulphur trioxide Steps in writing formula and names for covalent molecules 1. Asses the structure and determine how many atoms of each element exists in the structure. 2. Write the Formula by writing the symbol of the central atom/ atoms first and the other atoms next. Use subscripts to identify the number of each. Except water 3. Write the name of the formula by using the Prefixes that you have learnt. The prefix comes before the element name when writing the name of chemical formulas (See example 7). Please note there is no need to write mono if the first element is only one but you must use mono if the second element is only one( see example 5 and 6 ). 4. Change the last part of the name of the second element in the formula to “ide” 5. E.g CO2 is carbon dioxide 6. Eg. CO is Carbon monoxide 7. Eg. Se2Br2 is diselenium dibromide 8. More examples on slide 21 The prefix is placed BEFORE THE ELEMENT TO WHICH IT IS REFERRING afterwards you must end word in the prefix-ide. If you don’t see a subscript for the first element in the formula write the name of the first element as seen in periodic table. Special cases/ Special names--It is a good idea to learn the molecular formula of covalent compounds as you come across them as there are exceptions to the above rules as some names cannot be derived from their compounds/molecules eg. H2S hydrogen sulphide, Ammonia(NH3), methane for CH4, water H2O some of these were named long before it was discovered what atoms they consist of. PRACTICE Name the following covalent molecules N2O3 – N2O4- SF6- XeF6- CCl4 – CF4- SN- CONVERT THE FOLLOWING FROM WORD FORMULAS TO CHEMICAL FORMULAS Write the formula from the names of the covalent substances below 1. Selenium trioxide – 2. Carbon disulphide- 3. Carbon tetrabromide- 4. silicon dioxide- 5.silicon trioxide- 6. nitrogen dioxide- SPECIAL NAMES AND EXCEPTIONS H2O- water All acids eg HCl (Hydroclhoric acid), H2SO4(Sulphuric acid). Ammonia NH3 Ammonium NH4+ And all hyrdocarbons eg CH4 is methane THE DIATOMIC MOLECULES- All of these compounds can be found in nature as diatomic molecules. Meaning there is two atoms of the same kind combined together in a covalent bond like a set of twin holding hands. If any of these elements is being used or produced in a chemical reaction ensure the subscript two is beside them Eg. Structure of oxygen gas as found in nature Name ( in free state) Formula Hydrogen H2 Iodine I2 Bromine Br2 Chlorine Cl2 Oxygen O2 Nitrogen N2 Fluorine F2 POPULAR ACIDS – MEMORIZE THEM- YOU CAN CONSIDER THEIR NAMES AS SPECIAL CASES OF NAMES GIVEN FOR COVALENT SUBSTANCES WHICH THEY ARE Acid name Formula Hydrochloric acid HCl Hydrobromic Acid HBr Hydroiodic Acid HI hydrofluoric acid HF Hydrogen H2S Sulphide/hydrosulfuric acid CH3COOH Acetic acid/ Ethanoic acid H3PO4 phosphoric acid H2CO3 carbonic acid H2SO3 Sulfurous Acid H2SO4 Sulfuric acid HNO3 Nitric Acid HClO4 Perchloric Acid HClO3 Chloric Acid POPULAR BASES_ MEMORIZE THEM Potassium hydroxide -KOH Sodium hydroxide -NaOH Calcium hydroxide -Ca(OH)2 Barium hydroxide -Ba(OH)2 Lithium hydroxide -LiOH SECTION 2 Writing the Chemical equations for chemical reactions CHEMICAL CHANGE AND CHEMICAL RXN VS NON CHEMICAL CHANGE( PHASE TRANSITION) A chemical change results from a chemical reaction, while a non chemical reaction results from physical change when matter changes forms but not chemical identity. Examples of chemical changes are burning, cooking, rusting, and rotting. We can write chemical equations for them. Examples of physical changes are boiling, melting, freezing, sublimation, and depostition. No chemical equation is written for them. A chemical equation can only be written for a chemical reaction that brings about a chemical change. The chemical equation describes the chemical reaction. S WHAT IS A CHEMICAL REACTION A chemical reaction is one in which the reactants change chemically by forming new substances that are not reversible under most cases ( Note that reversible reactions exist). The equation for the reaction of hydrochloric acid with sodium metal can be denoted: 2Na(s)+2HCl(aq)→2NaCl(aq)+H2(g) 2H2(g) + O2(g)  2H2O(l) The following state symbols are utilized in chemical equation writing: (s) for solids( insoluble in water) or (l) for liquids, (g) for gases or (aq) for aqueous solutions( can dissolve in water hence soluble). DEFINITION OF A CHEMICAL EQUATION A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and formulae, wherein the reactant entities are given on the left-hand side and the product entities on the right-hand side. PARTS OF A CHEMICAL EQUATION 100 ‘c pd PARTS OF A CHEMICAL EQUATION CONTINUED UNDERSTAND IT BETTER LAW OF CONSERVATION OF MASS: MATTER CANNOT BE CREATED OR DESTROYED BUT ONLY CONVERTED FROM ONE FORM TO THE NEXT CONVERTING CHEMICAL EQUATIONS TO WORD CHEMICAL EQUATIONS The equation for the reaction of 2 mole of hydrochloric acid in aqueous state with 2 mole of solid sodium metal to produce 2 mole of aqueous sodium chloride and 1mole of hydrogen gas can be denoted: 2Na(s)+2HCl(aq)→2NaCl(aq)+H2(g) The following state symbols are utilized in chemical equation writing: (s) for solids( insoluble in water) or (l) for liquids, (g) for gases or (aq) for aqueous solutions( can dissolve in water hence soluble). SOLUBILITY RULES Rules used to determine the state of a chemical reactant or product in a chemical reaction. 1. All pure metals( in elemental state ) are solid in reaction except mercury. 2. Water is a liquid in most reactions unless it is a combustion reaction in which water will be a gas. 3. For diatomic nonmetals – H2(g), I2(s), Br2(l), Cl2(g), O2(g), N2(g) , F2( g) 4. All acids are aqueous 5. For the state of all salts and bases refer to the solubility table. If a substance is soluble it is aqueous, and if its insoluble it is solid. CONVERT THE FOLLOWING CHEMICAL EQUATIONS TO WORD CHEMICAL EQUATIONS AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq) One mole of aqueous silver nitrate reacts with one mole of potassium chloride in the aqueous state to produce one mole of silver chloride in the solid state and one mole of potassium nitrate in the aqueous state. 2KOH(aq) + CaCl2(aq)Ca(OH)2(aq) + 2KCl(aq) AgNO3(aq) + NaCl(aq) AgCl↓ + NaNO3 (aq) Mg(OH)2(s) + 2HCl (aq) MgCl2(aq) + 2H2O(l) CaO↓ + CO2(g)  CaCO3(s) LAW OF CONSERVATION OF MASS Matter cannot be created or destroyed but only converted from one form to the next. Try the following : Solid zinc metal reactc with silver oxide to produce solid zinc oxide and silver metal in the solid state. TYPES OF CHEMICAL REACTIONS To fully understand chemical reactions around us we must understand the different classifications of Chemical Equations. Therefore chemical equations may be classified as Convert from word to chemical equations 1. and balance solid magnesium metal react oxygen gas to produce solid ma oxide 2.Sodium metal reacts with ox to produce to solid sodium oxid _______________________________ 1.Convert from word equation t ___ equation : solid Calcium oxide d form calcium metal and oxygen _______________________________ 1. Convert from word equation to chemical equation and balance : solid iron metal reacts with copper (II) oxide to produce TYPES OF CHEMICAL REACTIONS CONTINUED Do the following and reacti balance: aqueous on copper(II) sulphate reacts with aqueus sodium hydroxide to produce solid( insoluble) copper (II) Do the following hydroxide and and sodium balance: sulphate.aqueous calcium hydroxide reacts with aqueous sulphuric acid to produce solid calcium sulphate and water in liquid state. hydroxide and aqueous sodium sulphate. TYPES OF CHEMICAL REACTIONS CONTINUED Combustion of hydrocarbon Combu st i)C2H4 (ii)Li Metal or non metal+ Mg(s) + O2(g) O2(g) give metallic oxide of non metal oxide MgO(s)  Take inventory of the elements & check if the equation is balanced or unbalanced , if not balanced proceed as follows  CONVERT TO CHEMICAL EQUATIONS AND BALANCING THE FOLLOWING Write the following and balance: solid magnesium metal reacts with oxygen gas to produce solid magnesium oxide Write the following and balance Sodium metal reacts with oxygen gas to produce to solid sodium oxide Write the following and balance: solid Calcium oxide decomposes to form calcium metal and oxygen Write the following and balance: solid iron metal reacts with copper oxide to produce solid copper metal and solid iron(II)oxide Write the following and balance: aqueous copper(II) sulphate reacts with aqueous sodium hydroxide to produce solid( insoluble) copper (II) hydroxide and sodium sulphate. Write the following and balance: aqueous calcium hydroxide reacts with aqueous sulphuric acid to produce solid calcium sulphate and water in liquid state. hydroxide and sodium sulphate. DETERMINING STATE SYMBOLS- SOLUBILITY RULES State symbols for a chemical reaction can be determined if you memorize your solubility rules table as the cations and anions of many compounds determine whether the compound will be insoluble in solution(solid), meaning it cant dissolve in water and is therefore called a precipitate which you will see as a solid in the reaction tube/ test-tube. A compound can be also be soluble( aqueous), meaning it can be dissolved in water and you will not see it as a precipitate when you react both reactants together in the test-tube. a. Please check open your solubility rules table. So solubility rules enable you to determine if ionic compounds are solid (s) or aqueous(aq) Moreover you must understand that metals are always solid except mercury which is a liquid metal. Diatomic molecules such as H2, O2, Cl2, N2, F2 are in gaseous state when in the equation, I2 is solid and Br2 is liquid. Elemental( free state) Sulphur exists in solid state) Covalent molcules such as CO2, CO and steam( H2O in gasesous state) are all gases (g) Water is always in liquid state unless it is a combustion reaction whereas water will be in the gaseous state(g) which is steam. All Acids are aqueous CONVERT AND COMPLETE (WHERE NECESSARY) THESE WORD EQUATIONS TO CHEMICAL EQUATIONS DETERMINE THEIR STATE SYMBOLS AND BALANCE THEM ALSO Convert the following word equations to chemical equations 1. Iron reacts with Sulphur to produce iron (II) Sulphide. 2. magnesium metal reacts with oxygen gas 3. Aluminum metal reacts with chlorine gas 4. Silver nitrate reacts with potassium chloride 5. Calcium chloride reacts with silver nitrate 6. Sodium Hydroxide reacts with Sulphuric acid 7. calcium hydroxide reacts with Phosphoric acid 8. calcium hydroxide reacts with hydrochloric acid CONVERTING WORD EQUATIONS TO CHEMICAL EQUATIONS AND BALANCE THEM Solid Copper metal reacts with oxygen gas to produce copper two oxide in solid state. CONTINUED STATE SYMBOL DETERMINATION AND SOLUBILITY RULES State symbols can be solid, liquid, gas, aqueous. However the diatomic gases are O2, H2, F2, Cl2, all these are gases(g), water( H2O can be gas( steam ) if the reaction is a combustion reaction, if not a combustion reaction the water will be in liquid state(l). Free state Metals( Mg, Ca, Al, Li) are always in solid state(s), except Hg which is a liquid at room temperature. All acids are aqueous state( aq) as all acids must first be dissolved in water to release its H+ ions. To determine whether your salt will be aqueous( salt is able to dissolve in water) you need to appreciate and understand the solubility rule table. You can have a solid salt or an aqueous salt /Double displacement  IONIC REACTION (PRECIPITATION REACTION) EQUATION The precipitation reaction starts with two soluble reactants anf leads to the formation of two products being formed, one will be a insoluble salt( precipitate) and the other will be a soluble salt. A balanced ionic equation shows the reacting ions in a chemical reaction. These equations are often used to model what happens in a precipitation reaction. In these reactions, two soluble reactants form an insoluble product and a soluble product. For example, silver nitrate solution reacts with sodium chloride solution. Insoluble solid silver chloride and sodium nitrate solution form: SPECTATOR IONS It is essential to understand that not all ions in a ionic equation( precipitation reaction) takes part in the chemical reaction to form the precipitate. The ions that do not participate in the double displacement reaction are called spectator ions and can be cancelled out. They will always remain unchanged after the reaction has occurred. THE IONIC EQUATION The ionic equation tells you what ions actually took part in the chemical reaction. STEPS IN WRITING A BALANCED IONIC EQUATION FROM PRECIPITATION REACTION. 1. Write the chemical equation with correct formulas 2. Balance the chemical equation 3. Write in the correct state symbols ( To do this you will have to had memorized your solubility rules which becomes an essential skill.) 4. Ionize/Dissociate (Split) any compounds that are in the aqueous state (aq) as this means they are in solution and hence form a homogenous solution where water is the solvent hence “Aqua”. You cannot dissociate compounds that are in the solid( s) , Liquid (l) or gaseous states) 5. Look for any spectator ions on both sides of the chemical equation and cancel them out( They don’t change, in state, charge, or amount of atoms and hence ARE SAME). 6. write the net ionic equation and check to ensure that the amount of charges on both sides is the same and elements. To show the ions involve we can dissociate(Split) all ions in aqueous state( you cannot split anything that is not aqueous). If we do this we would find that the Na+ ions and Cl- ions remain separate in the sodium nitrate solution and do not form a precipitate. Ions that remain separate during a reaction are called spectator ions, spectator ions remains unchanged in state, charge and amount of it on both sides of the equation. This means you can ignore them when you write the ionic equation. You only need to model how the solid silver chloride forms: Ag+(aq) + Cl-(aq) → AgCl(s) CHARCTERISTICS OF AN IONIC( PRECIPITATION) EQUATION In a balanced ionic equation: the number of positive and negative charges is the same the numbers of atoms of each element on the left and right are the same Example: Explain why this ionic equation is balanced: Ba2+(aq) + SO42-(aq) → BaSO4(s) There are the same numbers of atoms of each element on both sides of the equation. The total charge on both sides is also the same (zero). WRITE IONIC EQUATIONS FOR THE FOLLOWING QUESTIONS 1. lead II nitrate and Sodium chloride 2. Sodium carbonate and Iron II chloride 3. Potassium Iodide and Silver acetate 5. Lithium chloride and Silver sulphate 6.Ammonium phosphate and zinc nitrate