What is a compound? A substance in which the atoms of two or more different elements combine together Sodium chloride NaCl Carbon dioxide CO 2 Calcium carbonate CaCO 3 Aluminum sulfate Al 2 (SO 4 ) 3 Dinitrogen pentoxide N 2 O 5 Copper(II) chloride CuCl 2

Why do atoms of elements combine together? To reach the state of chemical stability

There are two ways to achieve chemical stability: 1. Transfer of valence electrons between atoms. A new ionic compound is formed (NaCl) 2. Share of valence electrons between atoms. A new covalent (molecular) compound is formed (H 2 O)

Ionic compounds Covalent (molecular) compounds  Composed of oppositely charged ions.  Crystalline solids at room temperature.  Hard and brittle.  High melting point.  Dissolve in water.  In solid state they don’t conduct electricity, but their liquid state and solutions in water conduct electricity  Composed of molecules.  Many are liquid and gases, some are solid.  The solid one have low melting point.  Some dissolve in water, many don’t dissolve in Water.  Don’t conduct electricity in pure state.

Ionic compounds

What is an ion ? An ion is a single atom (element) or a group of atoms that have a charge. A group of atoms that have a charge is called polyatomic ion. The charge on the ion is called oxidation number. Single atom ionsPolyatomic ions Na + Cl - Mg 2+ Ca 2+ S 2- O 2- B 3+ N 3- Li + P 3- Al 3+ I - NH 4 + HCO 3 - CO 3 2- C 2 H 3 O 2 - PO 4 3- H 3 O +

Ions formed from groups 1, 2, 13, 15,16, and 17 of the periodic table have a fixed oxidation number. Elements in groups 1, 2, 13 loose electrons so they have positive oxidation number equal to number of electrons they loose and they keep the name of the element. Elements in groups 15, 16, 17 may gain electrons so they have negative oxidation number equal to number of electrons they gain and the element name is modified to end with -ide

An ionic compound is composed of a positive ion and a negative ion. If the two ions (positive and negative) are single atom ions the ionic compound is called binary ionic compound. To name a binary ionic compound we start with the name of the positive ion and then the name of negative ion

Examples of naming binary ionic compounds (with fixed oxidation number) NaCl Na is sodium and it is in group 1 so it looses 1 electron and becomes Na + and called sodium ion Cl is chlorine and it is in group 17 so it gains 1 electron and becomes Cl - and called chloride ion So the name of the compound is sodium chloride

Examples of naming binary ionic compounds (with fixed oxidation number) Al 2 O 3 Al is aluminum and it is in group 13 so it looses 3 electrons and becomes Al 3+ and called aluminum ion O is oxygen and it is in group 16 so it gains 2 electron and becomes O 2- and called oxide ion So the name of the compound is aluminum oxide

Examples of naming binary ionic compounds (with fixed oxidation number) Ca 3 N 2 Ca is calcium and it is in group 2 so it looses 2 electron and becomes Ca 2+ and called calcium ion N is nitrogen and it is in group 15 so it gains 3 electron and becomes N 3 - and called nitride ion So the name of the compound is calcium nitride

Writing formula unit of binary ionic compounds Formula unit is the simplest ratio of ions in a compound. To write the formula unit of a binary ionic compound: 1. write the symbols of the elements in the compound in the same order as in the name. 2. Above the symbols write the oxidation number of each element without the charge. 3. Simplify the oxidation numbers if you can. 4. Write the simplified oxidation number of each element as a subscript for the other element. (if the simplified oxidation number is 1 don’t write it)

Examples on Writing formula unit of binary ionic compounds Sodium fluoride Na F The formula unit is NaF

Examples on Writing formula unit of binary ionic compounds Calcium oxide Ca O The formula unit is CaO

Examples on Writing formula unit of binary ionic compounds Aluminum sulfide 3 2 Al S The formula unit is Al 2 S 3

Some ions of elements have more than one oxidation number (like the transition elements). The oxidation number of such elements is always positive When such elements form ionic compound the oxidation number is represented by a roman numeral following the element’s name. For example: Fe with oxidation number +2 or Fe 2+ is written iron(II) Fe with oxidation number +3 or Fe 3+ is written iron(III) Copper(I) is Cu with oxidation number +1 or Cu 1+ Copper(II) is Cu with oxidation number +2 or Cu 2+ Remember: Numbers Roman symbol IIIIIIIVVVIVII

Examples of naming binary ionic compounds (when positive ion has more than one oxidation number) FeO Fe is iron and it has more than one oxidation number. Assume the oxidation number is x. O is oxygen and its oxidation number is -2. So 1(x) + 1(-2) = 0 (neutral compound) x = +2 So the name of the compound is iron(II) oxide

Examples of naming binary ionic compounds (when positive ion has more than one oxidation number) Fe 2 O 3 Fe is iron and it has more than one oxidation number. Assume the oxidation number is x. O is oxygen and its oxidation number is -2. So 2(x) + 3(-2) = 0 (neutral compound) x = +3 So the name of the compound is iron(III) oxide

Examples of naming binary ionic compounds (when positive ion has more than one oxidation number) Ni 3 N 4 Ni is nickel and it has more than one oxidation number. Assume the oxidation number is x. N is nitrogen and its oxidation number is -3. So 3(x) + 4(-3) = 0 (neutral compound) x = +4 So the name of the compound is nickel(IV) nitride

Copper(I) sulfide 1 2 Cu S The formula unit is Cu 2 S Examples on Writing formula unit of binary ionic compounds (with variable oxidation number)

Copper(II) sulfide Cu S The formula unit is CuS Examples on Writing formula unit of binary ionic compounds (with variable oxidation number)

Nickel(III) Phosphide Ni P The formula unit is NiP Examples on Writing formula unit of binary ionic compounds (with variable oxidation number)

Cobalt(III) oxide 3 2 Co O The formula unit is Co 2 O 3 Examples on Writing formula unit of binary ionic compounds (with variable oxidation number)

Complex ionic compounds Some ionic compounds are composed of an ion of an element and a polyatomic ion. A polyatomic ion is A group of covalently bonded atoms that acts together as one charged atom (ion). Examples of polyatomic ions: ammonium NH 4 phosphate PO 4 nitrite NO 2 nitrate NO 3 sulfite SO 3 sulfate SO 4 carbonate CO 3 hydrogen carbonate HCO

Examples on naming complex ionic compounds Name the compound (NH 4 ) 2 S? Solution: NH 4 is ammonium and has oxidation number Of +1 S is sulfur with oxidation number -2 So the name of the compound is ammonium sulfide

Examples on naming complex ionic compounds Name the compound CaCO 3 ? Solution: Ca is calcium and has oxidation number Of +2 CO 3 is carbonate with oxidation number -2 So the name of the compound is calcium carbonate

Examples on Writing formula unit of complex ionic compounds Write the formula of Aluminum hydroxide? 3 1 Al OH The formula unit is Al(OH) 3

Examples on Writing formula unit of complex ionic compounds Write the formula of Magnesium phosphate? 2 3 Mg PO 4 The formula unit is Mg 3 (PO 4 ) 2

Examples on Writing formula unit of complex ionic compounds Write the formula of Beryllium sulfate? Be SO 4 The formula unit is BeSO 4

Hydrates A hydrate is an ionic compound that has water chemically attached to its ions. If the water was removed from the hydrate it becomes anhydrous HydrateAnhydrous CuSO 4.5H 2 O Copper(II) sulfate pentahydrate blue crystals CuSO 4 Copper(II) sulfate white crystals

HydrateAnhydrous CoCl 2.6H 2 O Cobalt(II) chloride hexahydrate Pink crystals CoCl 2 Cobalt(II) chloride blue crystals Some ionic compounds can absorb water from air to become hydrates. These are called hygroscopic substances (example: Na 2 CO 3 ) If a hygroscopic absorbs enough water from air to become a liquid solution then it is called deliquescent. (Example: NaOH) Hygroscopic substances are used as drying agents or desiccants.

Naming and writing formulas of hydrates To name or write the formula of a hydrate you have to be familiar with the Greek prefixes of numbers.

Examples on naming hydrates Name the compound CaSO 4.2H 2 O? Solution: Ca is calcium with oxidation number +2 and SO 4 is sulfate with oxidation number -2 So the name of the compound is Calcium sulfate dihydrate (gypsum)

Examples on naming hydrates Name the compound NaOH.7H 2 O? Solution: Na is sodium with oxidation number +1 OH is hydroxide with oxidation number -1 So the name of the compound is sodium hydroxide heptahydrate

Examples on Writing formula unit of hydrates Write the formula of copper(II) sulfate pentahydrate? Cu SO 4 The formula unit is CuSO 4.5H 2 O

Examples on Writing formula unit of hydrates Write the formula of ammonium sulfite monohydrate? 1 2 NH 4 SO 3 The formula unit is (NH 4 ) 2 SO 3.H 2 O

Interpreting formulas The smallest unit of an ionic compound is called formula unit. So the formula unit of sodium chloride is NaCl the formula unit of calcium sulfate is CaSO 4 When we write 3CaSO 4, it means we have 3 formula units of calcium sulfate.

What does a formula of a compound tell us? It tells us the elements found in the compound and the exact number of atoms of each compound. Example: What information does the formula of Al 2 O 3 tell you about the number of atoms of each element that are present? It tells us that there are 2 atoms of aluminum and 3 atoms of oxygen

Example: What information does the formula of Mg(OH) 2 tell you about the number of atoms of each element that are present? It tells us that there are 1 atom of magnesium, 2 atoms of oxygen and 2 atoms of hydrogen

Example: What information does the formula of 2Ca(NO 3 ) 2.2H 2 O tell you about the number of atoms of each element that are present? It tells us that there are 2 atoms of calcium, 4 atoms of nitrogen, 16 atoms of oxygen and 8 atoms of hydrogen

Properties of Ionic Compounds Composed of oppositely charged ions. Crystalline solids at room temperature. Hard and brittle. High melting point. Dissolve in water. In solid state they don’t conduct electricity, but their liquid state and solutions in water conduct electricity