Chemical Formulas and Binary Compounds

• Chemical formulas show the kind and number of atoms in the smallest representative unit of a substance.
• Example of a chemical formula: NaCl.
• Naming compounds and writing formulas depends on the ability to recognize ionic and molecular compounds.
• Compounds are divided into binary and ternary types.

Binary Compounds

• True binary compounds contain only two elements.
• The name of every binary compound ends with "ide".
• Binary compounds come in three types.
• Type I compounds involve a metal that forms only one type of cation.
• Type II compounds involve a metal that forms two or more types of cations.
• Type III compounds contain only non-metals.
• Cations are positively charged atoms, example Na+.
• Anions are negatively charged atoms, example Cl-.
• Group I elements have a +1 ionic charge.
• Group II elements have a +2 ionic charge.
• Group III elements have a +3 ionic charge.
• Group IV elements have a +4 ionic charge.
• Group V elements have a 3- ionic charge.
• Group VI elements have a 2- ionic charge.
• Group VII elements have a 1- ionic charge.
• Group VIII elements are noble gases

Rules for Naming Type I Binary Compounds

• Type I binary compounds contain metals present in Group 1 or Group 2 of the periodic table.
• The cation is named first, followed by the anion.
• Simple cations (from a single atom) use the element's name.
• Simple anions (from a single atom) are named by taking the root of the element name and adding "IDE."
• The compound's name combines the names of the ions.

Naming Compound Examples

• To name RbI: Rb is rubidium, I is iodine (root "iod"), so the name is rubidium iodide.
• To name CaO: Ca is calcium, O is oxygen (root "ox"), so the name is calcium oxide.

Writing Formulas for Compounds

• For Potassium Sulfide, potassium is K (+1 oxidation), sulfur is S (-2 oxidation), creating K₂S.
• For Magnesium Chloride, magnesium is Mg (+2 oxidation), chlorine is Cl (-1 oxidation), creating MgCl₂

Rules for Naming Type II Binary Compounds

• Type II binary compounds contain metals not found in Group 1 or Group 2 of the periodic table.
• The cation is named first, followed by the anion.
• A simple cation is named after its element, with a Roman numeral indicating its oxidation number.
• A simple anion is named using the root of the element name plus "IDE".
• The compound's name combines the names of the ions.

Using Roman Numerals

• 1 is I
• 2 is II
• 3 is III
• 4 is IV
• 5 is V
• 6 is VI
• 7 is VII
• 8 is VIII
• 9 is IX
• 10 is X

Naming Compounds Examples with Roman Numerals

• For FeCl₂, Fe is iron, Cl is chlorine (giving chloride).
• Determine the charge of the anion in order to find the Roman numeral.
• Cl has a -1 charge.
• Multiply the number of atoms to get the total negative charge. (2 times -1 = -2)
• Balance total negative charge with a total positive charge (+2)
• Divide the total positive charge by the number of atoms to get the Roman numeral (+2 divided by 1 Fe = +2, which is II), yielding Iron (II) Chloride.
• Pb is lead, S is sulfur (giving sulfide).
• Determine the charge of the Roman numeral: S= -2
• There are 2 sulfur atoms, therefore 2 x -2= -4. <---- charge is negative
• The total positive charge must +4
• There is one lead atom +4/1 = +4 (IV), yielding lead (IV) sulfide

Writing the Formula for Compounds

• The chemical symbol of nickel (III) oxide is Ni, the oxidation state is +3. Oxide is derived from oxygen, whose symbol is O and its oxidation state is -2
• To balance charges find the least common multiple (LCM) of 3 and 2 is 6 which means you need two Ni atoms and three O atoms to balance the charges to get Ni₂O₃
• The chemical symbol of lead (IV) nitride is Pb with an oxidation state of +4. Nitride is derived from nitrogen whose symbol is N and its oxidation state is -3
• To balance charges, find the LCM of 4 and 3 which is 12. You need 3Pb atoms and 4N atoms to balance the charges to get Pb₃N₄
• The chemical symbol of iron (II) oxide is Fe, and the oxidation state is +2. Oxide is a form of oxygen, whose symbol is O and its oxidation state is -2
• Since charge is balanced, no work has to be done, to get FeO

Type III Binary Compounds

• These compounds contain no metal atoms. Naming follows two systems, "old" and "new."
• The new system is identical to that used for type II compounds.
• It is important to only one can be used at a time for type III binary systems, and do not mix the systems.

Old system naming for Binary Compounds

• The first element's full name is used.
• The second element is named as an anion.
• Prefixes denote the number of atoms present.
• The prefix mono- is never used for the first element.

Covalent Prefixes

• Mono is 1
• Di is 2
• Tri is 3
• Tetra is 4
• Penta is 5
• Hexa is 6
• Hepta is 7
• Octa is 8
• Nona is 9
• Deca is 10

Naming Type III Examples

• CO₂ becomes Carbon Dioxide. Di= 2 oxygen
• N₂ becomes dinitrogen monoxide
• PCl₃ becomes Phosphorous Trichloride. All binary compounds end in ide!!!

Naming Type III Binary Compounds the New System

• The cation is always named first and the anion second.
• A simple cation takes it's name from the name of the element which includes a roman numeral to indicate it's oxidation number
• A simple anion is named from a single atom that is named by taking the first part of the first element (root) and by adding the letters "IDE"

Examples of the New System Type III Naming

• NO₂ is Nitrogen (IV) oxide
• N₂O is nitrogen (I) oxide Write the formula for carbon (iv) chloride
• The symbol for carbon is C has an oxidation state of 4+ as given by the roman numeral. Chloride is the derived from chlorine where is charge is -1
• The LCM of 4 and 1 is 4, to get CCl₄
• The symbol for nitrogen (V oxide) is N whose numeral indicates that a charge is +5. Oxide is derived from oxygen with a charge of -2
• So far we have N O, the LCM of 5 and 2 is 10 which need 2N atoms and 5 oxygen atoms to balance the charges which is N₂O₅

Binary Compound Guide

• Type 1: Metal + non-metal's root word + ide
• Type 2: Metal + charge of metal (Roman numeral) + non-metal's root word + ide
• Type 3 (Old method): Prefix (except mono) + non-metal + prefix + non-metal's root word + ide
• Type 3 (New method): Non-metal + charge of non-metal (roman numeral) + non-metal's root word + ide

TERNARY COMPOUNDS

• Type 1: Metal + polyatomic ion
• Type 2: Metal + charge of metal + polyatomic ion

Ternary Compound Naming

(A.K.A. Compounds that contain polyatomic ions)

• An ion is an atom with an electrical charge
• A polyatomic ion is a group of atoms with an electrical charge, acting like a single atom
• The names almost always end in -ate or -ite. Exceptions are cyanide, hydroxide, and peroxide

Naming Ternary Compounds

• Follow the naming system for Type I and Type II binary compounds while making sure not to change the name for polyatomic ions Polyatomic ions end in -ate or -ite:
• PO₄³⁻ = phosphate
• SO₄²⁻ = sulfate
• NO³⁻ = nitrate
• ClO³⁻ = chlorate
• CO₃²⁻ = carbonate
• PO₅³⁻ = perphosphate
• PO₄³⁻ = phosphate (most common)
• PO₃³⁻ = phosphite
• PO₂³⁻ = hypophosphite
• SO₅²⁻ = persulfate
• SO₄²⁻ = sulfate (most common)
• SO₃²⁻ = sulfite SO₂²⁻ = hyposulfite