Mission B5 - How do you Name and Write chemical formulas for Compounds?

“Not Just James Bond”

Part 1 - Naming Binary Compounds• Binary compounds – elements with only two

types of atoms in it

• Naming binary compounds is simple– It is based on the names of the cations and

anions and all binary compounds end in -ide

• Examples:– NaCl = sodium chloride

– CaF2 = calcium fluoride

– Al2O3 = aluminum oxide

– BaO = barium oxide

Part 2 - Naming Transition Metal Compounds

• Similar to naming binary compounds

• But transition metals have multiple oxidation states (can have different charges)

• Steps

– determine the oxidation number of the nonmetal

– use the rules of oxidation states to solve

– determine the oxidation number of the nonmetal

– The name must have Roman numerals to show the oxidation state of the metal

Example: CuCl2 • Step 1

– determine the charge on the chlorine– Chlorine has a higher EN therefore will be a

negative oxidation state which is -1– But there are two chlorines so the total is -2

• Step 2 – Determine the charge on the copper – The compound’s total charge must equal zero– Copper must be a +2 charge to balance the

chlorine

• Therefore CuCl2 is called copper II chloride

Example: In FeCl3

Step 1

– what is the charge on the chlorine?

-1 = it has the higher electronegativity and is negative

– What is the total charge of 3 chlorines?

-3 = 3 x -1

Step 2

– what is the charge on FeCl3?

Zero = charges in compounds add up to 0

– What is the charge on the iron then?

+3 = chlorine’s -3 + iron’s +3 = 0

What is the name of the particle FeCl3 then?

– iron III chloride = “III” shows the iron’s charge

Part 3 - Naming Polyatomic Compounds

• Polyatomic ions– Groups of atoms that have a

collective charge on them– See CRTable E– Similar to binary naming– If more than two elements in the

compound, look up the polyatomic ion on Table E

– Example

[Na]+ + [SO4] 2- Na2SO4

sodium + sulfate = sodium sulfate

Naming Polyatomic Compounds

• Examples

• Na2CO3

= sodium carbonate

• HCN

= hydrogen cyanide

• KClO3

= potassium chlorate

• NH4Cl

= ammonium chloride

Part 4 - Naming Molecular Compounds • Naming molecular

compounds (covalently bonded substances) is similar to naming ionic ones with one exception:– When naming

substances with all nonmetals

– Prefixes are used to designate the number of atoms of each

Prefix # of Atoms

Formula example

Name

mono 1 CO Carbon monoxide

di 2 CO2 Carbon dioxide

tri 3 SO3 Sulfur trioxide

tetra 4 CCl4 Carbon tetrachloride

penta 5 PCl5 Phosphorus pentaflouride

Examples of Naming Covalent Compounds

• Examples:

– CO - carbon monoxide

– CO2 - carbon dioxide

– SO2 - sulfur dioxide

– N2O3 - dinitrogen trioxide

– SF6 - sulfur hexafluoride

– H2O - dihydrogen monoxide

Writing Formulas• When writing chemical formulas

• Reverse the rules for writing chemical names

• Here are examples of each type of chemical formula

• Ex 1 - Binary compound - sodium chloride

– sodium’s oxidation number is Na+1

– chlorine’s oxidation number is Cl-1

– Charges are equal and cancel each other

– Therefore the chemical formula = NaCl

Writing Chemical Formulas

• Ex 2 - Binary compound - aluminum chloride– one aluminum has is Al+3 – one chlorine is Cl-

– It takes one Al+3 to balance the charge of three Cl-

– Therefore the formula for aluminum chloride is AlCl3

• Ex 3 - Transition metals – iron II oxide– one iron II has a charge of Fe+2 – one oxygen has a charge of O-2 – The two charges balance out to a 1:1 ratio

– Therefore the formula for iron II oxide is FeO

Writing Chemical Formulas

• Ex 4 - Nonmetal-nonmetal compounds - dinitrogen trioxide

– Oxidation numbers aren’t required in writing this formula

– Dinitrogen is two nitrogens

– Trioxide is there oxygens

– Therefore the formula for dinitrogen trioxide is N2O3

Writing Chemical Formulas

• Ex 5 - Polyatomic ions – magnesium nitrate

– Magnesium (Mg+2) is in Group 2 and has a +2 oxidation charge

– Nitrate (NO3-) is a polyatomic ion from

Table E with an oxidation number of -1

– So two nitrates are needed to balance the one magnesium and give a zero charge

– Therefore the formula for magnesium nitrate is Mg(NO3)2

Writing Chemical Formulas

• Ex 6 - Polyatomic ions and transition metals – copper I sulfate

– Copper (Cu+1) has a +1 charge as per the Roman numeral

– Sulfate (SO4-2) is a polyatomic ion from

Table E with an oxidation number of -2

– So two coppers are needed to balance the one sulfate and give a zero charge

– Therefore the formula for copper I sulfate is Cu2 SO4

Writing Chemical Formulas

• A short cut – the Criss-Cross method of writing

– Look at the oxidation states of the elements in the compound

– cross the numbers, drop the charges, and you will have the formula

– Example – lead II chloride

• Lead +2 charge

• Chlorine -1 charge

Pb +2 Cl -1 Pb1Cl2