CHAPTER 7: CHEMICAL FORMULAS AND CHEMICAL COMPOUNDS Chemistry 1-2 Enriched Mr. Chumbley
SECTION 1: CHEMICAL NAMES AND FORMULAS While the bulk of the content will come from the Naming Chemical Compounds & Writing Chemical Formulas packet, some of the definitions of terms do come from various chapters and sections within the book.
Chemical Formulas A chemical formula is used to tell both number and kind of atoms within a compound A chemical formula combination of chemical symbols and numbers to represent a substance Examples of a chemical formula include: H 2 O CO 2 C 6 H 12 O 6
Chemical Formulas Within any chemical formula, there are two parts Chemical symbols tell you the kind of atoms Subscripts tell you the number of each atom or compound C 8 H 18 Al 2 2( (SO 4 4) ) 3
Chemical Compounds There are two types of chemical compounds that we will be naming Molecular compounds and ionic compounds We will discuss what these compounds are at a later time, but know that the way in which each type is formed is different
Ions In order to name ionic compounds, we need to understand what an ion is An ion is an atom or molecule that has gained or lost one or more electrons and has a negative or positive charge Monatomic ions are made from a single atom Polyatomic ions are made of two or more atoms
Ions Similar to how atoms of the same element can have multiple isotopes, atoms of the same element can have multiple ions Cations are positively charged ions Anions are negatively charged ion
Naming Monatomic Ions Before we start looking at how to name compounds, it is beneficial to know how to name single atoms All ions can be written using the chemical symbol and the charge of the ion K + Mg 2+ F - N 3- There are three ways to name monatomic ions based on their location and charge
Naming Cations Cations are the simplest ion to name Cations use the name of the element, followed by the numerical value of the charge, followed by the positive/negative sign Mg 2+ Is read as magnesium two plus
Naming Anions Anions are slightly more complicated Anions take the root of the element, and add ide to the end N 3- Is read as nitride
Transition Metal Ions Element located in the middle of the table are called transition metals, and can carry different charges Naming these ions uses a what is called the stock system This will be covered when we get to compounds that use these particular ions
Ions on the Periodic Table Specific groups within the periodic table can be identified by the ions elements within that family form Alkali metals : 1+ (plus Ag) Alkaline Earth metals: 2+ (plus Zn and Cd) Group 13 : 3+ Group 15 : 3 Group 16 : 2 Halogens : 1 1+ 4+ or 2+ 3+ 4 3-2- 1- Li Be N O F Na Mg Al P S Cl K Ca Zn Ga As Se Br Rb Sr Ag Cd In Te I Cs Ba Fr Ra
NAMING BINARY COMPOUNDS
Binary Compounds All binary compounds contain only two elements Every binary compound ends with ide There are three types
Type I Binary Compounds Type I compounds are made up of a cation of fixed charge, taken from either Group 1 or Group 2 on the periodic table The anion from a Type I compound is taken from the opposite side of the periodic table, taken from one of the elements with fixed anions The net charge for the compound is always zero
Rules for Naming Type I Binary Compounds 1. The cation is always named first and the anion second 2. A simple cation (obtained from a single atom) takes its name from the name of the element 3. A simple anion (obtained from a single atom) is named by taking the first part of the element name (the root) and adding the letters ide 4. Write the name for the compound by combining the names of the ions
Example 1-1 Name the compound RbI Rb is the chemical symbol for rubidium I is the chemical symbol for iodine Root is iod Add ide to the end to create iodide Put the two together to get the name rubidium iodide
Example 1-2 Name the compound CaO Ca is the chemical symbol for calcium O is the chemical symbol for oxygen Root is ox Add ide to the end to create oxide Put the two together to get the name calcium oxide
Example 1-3 Name the compound Li 3 N Li is the chemical symbol for lithium N is the chemical symbol for nitrogen Root is nitr Add ide to the end to create nitride Put the two together to get the name lithium nitride
Example 1-4 Write the formula for potassium sulfide. The chemical symbol of potassium is K Its ionic charge is +1 Sulfide is derived from sulfur, whose symbol is S Its ionic charge is -2. The total positive charge must balance the total negative charge Therefore, we need 2 potassium atoms to give a total positive charge of +2 to balance the -2 charge of the sulfur. Putting it all together we have K 2 S
Example 1-5 Write the formula for magnesium chloride. The chemical symbol of magnesium is Mg Its ionic charge is +2 Chloride is derived from chlorine, whose symbol is Cl Its ionic charge is -1. The total positive charge must balance the total negative charge Therefore, we need 2 chlorine atoms to give a total negative charge of -2 to balance the +2 charge of the magnesium Putting it all together we have MgCl 2.
Type II Binary Compounds Type II compounds are formed from metals that are not found in Group 1 or Group 2 of the periodic table The ionic charge of the metal in the compound is not fixed, but the ionic charge of the nonmetal is The ionic charge of the metal is indicated through the use of a Roman numeral This naming scheme is referred to as the stock system
Type II Cations Transition metals are capable of having multiple ions of different charge Sc Ti V Cr Mn Fe Co Ni Cu Ge Y Zr Nb Mo Tc Ru Rh Pd Sn Sb Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At
Type II Binary Compounds Typically the charge of the metal is between 2-4 Roman numerals are used to indicate the charge of the metal ion Number Roman Numeral 1 I 2 II 3 III 4 IV 5 V 6 VI 7 VII 8 VIII 9 IX 10 X
Rules for Naming Type II Binary Compounds 1. The cation is always named first and the anion second 2. A simple cation (obtained from a single atom) takes its name from the name of the element 3. A Roman numeral indicates the ionic charge on the metal cation. 4. A simple anion (obtained from a single atom) is named by taking the first part of the element name (the root) and adding the letters ide 5. Write the name for the compound by combining the name of the cation, the Roman numeral, and the name of the anion
Example 2-1 Name the compound FeCl 2 Fe is the chemical symbol for iron Fe is not in Group 1 or Group 2, therefore a Roman numeral is needed in the name Cl is the chemical symbol for chlorine Root is chlor Add ide to the end to create chloride At this point we have iron (??) chloride To find the Roman numeral Find the charge of the anion. Cl has a -1 charge. Multiply times the number of those atoms to get the total negative charge There are 2 Cl atoms, so the total negative charge is -2 Balance total negative charge with total positive charge The total negative charge of -2 must be balanced with a total positive charge of +2 Divide the total positive charge by the number of atoms to get Roman numeral Since there is only 1 Fe atom, the charge must be +2; so the Roman numeral is II Put the pieces together to get the name iron (II) chloride
Example 2-2 Name the compound PbS 2 Pb is the chemical symbol for lead Pb is not in Group 1 or Group 2, therefore a Roman numeral is needed in the name S is the chemical symbol for sulfur Root is sulf Add ide to the end to create sulfide At this point we have lead (??) sulfide To find the Roman numeral Find the charge of the anion. S has a -2 charge. Multiply times the number of those atoms to get the total negative charge There are 2 S atoms, so the total negative charge is -4 Balance total negative charge with total positive charge The total negative charge of -4 must be balanced with a total positive charge of +4 Divide the total positive charge by the number of atoms to get Roman numeral Since there is only 1 Pb atom, the charge must be +4; so the Roman numeral is IV Put the pieces together to get the name lead (IV) sulfide
Example 2-3 Write the formula for nickel (III) oxide The chemical symbol for nickel is Ni The ionic charge is +3, given by the Roman numeral Oxide is derived from oxygen, whose symbol is O Its ionic charge is -2 At this point we have Ni O The total positive charge must balance the total negative charge To balance the positive and negative charge, we find that the least common multiple of 3 and 2 is 6 This means that there are 2 Ni atoms to make +6 and 3 O atoms to make -6 Putting it all together we have Ni 2 O 3
Example 2-4 Write the formula for lead (IV) nitride The chemical symbol for lead is Pb The ionic charge is +4, given by the Roman numeral Nitride is derived from nitrogen, whose symbol is N Its ionic charge is -3 At this point we have Pb N The total positive charge must balance the total negative charge To balance the positive and negative charge, we find that the least common multiple of 3 and 4 is 12 This means that there are 3 Pb atoms to make +12 and 4 N atoms to make -12 Putting it all together we have Pb 3 N 4
Example 2-5 Write the formula for iron (II) oxide The chemical symbol for iron is Fe The ionic charge is +2, given by the Roman numeral Oxide is derived from oxygen, whose symbol is O Its ionic charge is -2 At this point we have Fe O The total positive charge must balance the total negative charge Since the charges are already balanced we know that there is 1 Fe atom and 1 O atom Putting it all together we have FeO
Type III Binary Compounds Type III compounds are compounds that contain no metal ions The naming system for this type of compound is based on the number of atoms of each element Number Prefix 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca
Rules for Naming Type III Binary Compounds 1. The first element in the formula is named first, and the full element name is used 2. The second element is named as though it were an anion: root + ide 3. Prefixes are used to denote the numbers of atoms of each element present 4. The prefix mono- is never used for naming the first element.
Example 3-1 Name the compound NO 2. N is the chemical symbol of nitrogen Since there is only one nitrogen atom AND it is the first element the prefix mono is not used. O is the chemical symbol of oxygen, whose root is ox. Add the -ide ending to get oxide There are two oxygen atoms so we also add the prefix di to get dioxide Put the pieces together to get the name nitrogen dioxide
Example 3-2 Name the compound N 2 O. N is the chemical symbol of nitrogen Since there are two nitrogen atoms we need to add the prefix di to get dinitrogen O is the chemical symbol of oxygen, whose root is ox. Add the -ide ending to get oxide There is only one oxygen atom we add the prefix mono (mono IS used for the second element) to get monoxide Put the pieces together to get the name dinitrogen monoxide
Example 3-3 Write the formula for carbon tetrachloride. Carbon The chemical symbol of carbon is C No prefix before carbon means there is only 1 atom present Tetrachloride Chloride is derived from chlorine, whose symbol is Cl The prefix tetra means there are 4 atoms present Thus, there are 4 Cl atoms in the chemical formula Putting it all together we have CCl 4
Example 3-4 Write the formula for dinotrogen pentaoxide. Dinitrogen The chemical symbol of carbon is N The prefix di before means there are 2 atoms present Thus, there are 2 N atoms in the chemical formula Pentaoxide Oxide is derived from oxygen, whose symbol is O The prefix penta means there are 5 atoms present Thus, there are 5 O atoms in the chemical formula Putting it all together we have N 2 O 5
NAMING NON-BINARY COMPOUNDS
Ternary Compounds Ternary compounds are those that contain polyatomic ions Polyatomic ions are made up of more than one atom that act as a single unit Most polyatomic ions have a negative charge, with the notable exception of ammonium (NH 4 1+ ) Nearly all polyatomic ions end with ate or ite Cyanide (CN 1- ) Hydroxide (OH 1- ) Peroxide (O 2 2- )
Naming Ternary Compounds Naming ternary compounds is very similar to naming Type I or Type II binary compounds If the polyatomic is first, the compound is named like a Type I compound name of polyatomic ion + root+ide If the polyatomic ion is second and the cation is from Group 1 or Group 2, the compound is named like a Type I compound name of element + root+ide If the polyatomic ion is second and the cation is a transition metal, the compound is named like a Type II compound name of element + (Roman numeral) + root+ide
Example 4-1 Name the compound NH 4 Cl. NH + 4 is the chemical formula of ammoinum Since the polyatomic ion is first, no roman numeral is needed Cl is the chemical symbol of chlorine, whose root is chlor- Add the -ide ending to get chloride Put the pieces together to get the name ammonium chloride
Example 4-2 Write the formula for ammonium sulfide. Ammonium is NH 4 + The charge of ammonium is known to be +1 Sulfide is derived from sulfur, whose symbol is S The charge of sulfur is known to be -2 The total positive charge must balance the total negative charge There needs to be 2 ammonium ions to balance out the charge of 1 sulfide ion Put the pieces together to get the name (NH 4+ ) 2 S
Example 4-3 Name the compound Na 2 SO 4 Na is the chemical symbol for sodium Since sodium is in Group 1, no Roman numeral is needed SO 4 2- is the chemical symbol for a sulfate ion Put the two together to get the name sodium sulfate
Example 4-4 Name the compound CrPO 4 Cr is the chemical symbol for chromium Cr is not in Group 1 or Group 2, therefore a Roman numeral is needed in the name PO 4 is the chemical formula for a phosphate ion To find the Roman numeral Find the charge of the anion. PO 4 has a -3 charge. Multiply times the number of those atoms to get the total negative charge There is 1 PO 4 ion, so the total negative charge is -3 Balance total negative charge with total positive charge The total negative charge of -3 must be balanced with a total positive charge of +3 Divide the total positive charge by the number of atoms to get Roman numeral Since there is only 1 Cr atom, the charge must be +3; so the Roman numeral is III Put the pieces together to get the name chromium (III) phosphate
Example 4-5 Write the formula for potassium cyanide The chemical symbol of potassium is K Its ionic charge is +1 Since potassium is in Group 1, no Roman numeral is needed The formula for cyanide is CN - Its ionic charge is -1. The total positive charge must balance the total negative charge Therefore, we need 1 potassium atoms balance the -1 charge of the 1 cyanide ion Putting it all together we have KCN
Example 4-6 Write the formula for iron (III) chromate The chemical symbol of iron is Fe The Roman numeral tells us that the charge is +3 The formula for chromate is CrO 4 2- Its ionic charge is -2. The total positive charge must balance the total negative charge To balance the positive and negative charge, we find that the least common multiple of 2 and 3 is 6 This means that there are 2 Fe atoms to make +6 and 3 CrO 4 2- ions to make -6 Putting it all together we have Fe 2 (CrO 4 ) 3
Naming Polyatomic Ions with Oxygen There are a number of polyatomic ions that are very similar in name and composition, with the key difference being the number of oxygen atoms The way in which these ions are named is based off the most common ion Formula CO 3 2- ClO 3 - NO - 3 PO 3-4 SO 2-4 Name carbonate chlorate nitrate phosphate sulfate
Naming Polyatomic Ions with Oxygen Number of Oxygen Two less oxygen One less oxygen Most common One more oxygen Nomenclature hypo ite ite ate per ate The ion that is the most common ends in ate Ions with more or less oxygen have names based on the number difference
Naming Polyatomic Ions with Oxygen Some examples: Formula Name Formula Name PO 5 3- perphosphate NO 4 - pernitrate PO 4 3- phosphate NO 3 - nitrate PO 3 3- phosphite NO 2 - nitrite PO 2 3- hypophosphite NO - hyponitrite While not all of these ions exist in the real world, the can still be used to demonstrate the naming convention
Naming Acids For this class, all acids will begin with hydrogen (H) All acids end with the word acid There are two types of acids we will name: Acids that DO NOT contain oxygen Acids that DO contain oxygen
Naming Acids that Do Not contain Oxygen To name acids without oxygen, the nomenclature is simple 1. The hydrogen is replaced with the prefix hydro 2. The suffix ic is added to the root of the non-hydrogen anion 3. The word acid is added to the end 4. The result is in the form of hydro ic acid
Example 5-1 Name the compound HF. We know this is an acid because the chemical formula starts with H Take the name of the anion (fluoride) add the prefix hydro and change the ending to ic : hydrofluoric Finally, add the word acid to make hydrofluoric acid
Example 5-2 Name the compound HCN. We know this is an acid because the chemical formula starts with H There is no oxygen present so we start with the prefix hydro Next, take the name of the anion (cyanide) and change the ending to ic : hydrocyanic Finally, add the word acid to make hydrocyanic acid
Example 5-3 Write the formula for hydrobromic acid. We know the formula starts with H because it is an acid The charge on H is +1 We also know that the acid does not contain oxygen because of the hydro prefix Removing the hydro and ic leaves us with brom, the root of bromine or Br The charge on bromine is -1 The total positive charge must balance the total negative charge There must be 1 H atoms to balance the charge of 1 bromine atom Balance the charges to get the formula HBr
Example 5-4 Write the formula for hydrosulfuric acid. We know the formula starts with H because it is an acid The charge on H is +1 We also know that the acid does not contain oxygen because of the hydro prefix Removing the hydro and ic leaves us with sulfur The charge on sulfur is -2 The total positive charge must balance the total negative charge There must be 2 H atoms to balance the charge of 1 sulfur atom Balance the charges to get the formula H 2 S
Naming Acids that Do Contain Oxygen Acids that contain oxygen will be polyatomic ions 1. Find the name of the polyatomic ion 2. If the name of the ion ends in ate change it to ic 3. If the name of the ion ends in ite change it to ous 4. Add the word acid to the end 5. The result is ic acid or ous acid
Example 6-1 Name the compound HClO 4. We know this is an acid because it starts with H ClO 4 - is the perchlorate ion Change the ate to ic and get perchloric Add the word acid and get perchloric acid
Example 6-2 Name the compound H 2 SO 3. We know this is an acid because it starts with H SO 3 2- is the sulfite ion Change the ite to ous and get sulfous Add the word acid and get sulfous acid The name is actually sulfurous acid, which differs from the root for sulfur.
Example 6-3 Write the formula for phosphorous acid. The word acid tells us the first element is H The charge on H is +1 We also know it is a ternary acid because the prefix hydro (meaning binary acid) is missing Change ous to ite to get phosphite The formula for phosphite is PO 3 3- The total positive charge must balance the total negative charge There must be 3 H atoms to balance the charge of 1 phosphite ion Putting it together and balancing the charges we get H 3 PO 3
Example 6-4 Write the formula for carbonic acid. The word acid tells us the first element is H The charge on H is +1 We also know it is a ternary acid because the prefix hydro (meaning binary acid) is missing Change ic to ate to get carbonate The formula for carbonate is CO 3 2- The total positive charge must balance the total negative charge There must be 2 H atoms to balance the charge of 1 carbonate ion Putting it together and balancing the charges we get H 2 CO 3
Hydrates Many of the Type I, Type II, and Ternary compounds are categorized as inorganic salts When some of these salts form, they crystalize with water molecules The amount of water molecules in the compound is a whole number ratio and is written as part of the formula MgSO 4 7H 2 O
Naming Hydrates The salt portion of the hydrate is named as it exists without the water The number of water molecules is indicated by using the numerical prefixes before the word hydrate Number Prefix 1 mono 2 di 3 tri 4 tetra 5 penta 6 hexa 7 hepta 8 octa 9 nona 10 deca
Example 7-1 Name the compound AlCl 3 6H 2 O The name of the salt is as it would be named without the water, aluminum chloride The hydrate portion contains 6 molecules of water, so it becomes hexahydrate Put both parts together to get aluminum chloride hexahydrate
Example 7-2 What is the chemical formula for sodium sulfate decahydrate? The chemical formula for sodium sulfate is Na 2 SO 4 The hydrate has the prefix of deca, meaning there are 10 H 2 O molecules The formula is written as Na 2 SO 4 10H 2 O