Ions and Ionic Bonds

Review Octet Rule

Atoms typically gain or lose valence e- so they will have the same e- configuration as a noble gas.

Most noble gases have 8 valence electrons. Helium has only 2 valence electrons.

The Octet Rule

Na Ne

8 valence electrons

1 valence electron

8 valence electrons

The Octet Rule

8 valence electrons

Cl

7 valence electrons

Ar

8 valence electrons

The Octet Rule

Li He

2 valence electrons

1 valence electron

2 valence electrons

•Ionic bonds are a type of chemical bond based on electrostatic forces between two oppositely-charged ions.

Ionic Bonds

•It is basically the transfer of one electron from one atom to another

•An ion is an atom or group of atoms that have a charge. Atoms normally have a neutral charge because most often they have the same number of electrons and protons. They become ions by the loss or addition of one or more electrons. This process is called ionization.

Ionic Bonds

•An ion that has more electrons than protons is called an anion, and an ion that has fewer electrons than protons is called a cation.

Ionic Bonds

•The name ion was given by a man named Michael Faraday, which comes from a Greek word meaning “to go” or “a goer”.

•The word anion comes from the Greek word meaning (a thing) “going up” and cation means (a thing) “going down”.

Ionic Bonds

Ionic Compounds Ionic compound (salt) – compound made of

cations and anions. cations are formed from metals anions are formed from non-metals

Ionic bond – the force that holds an ionic substance together.

Ionic Bonding

Na Cl

Na Cl+ -

Ionic bonds Occurs when:

1. a metal atom loses an electron and becomes a positive ion

2. a non-metal atom gains the electron and becomes a negative ion

3. the positive and negative attract each other and form a bond

Ionic Bonding

+

-- +

-- +

-- +

-

+

-

+

- +

-

+

- +

-

+

- +

-

+

-

+

- +

-

+

- +

-

+

- +

-+ + +

+ - + - + - +IMPORTANT: Although the ions in a salt are charged, the compound as a whole is not.

How do ionic bonds form Use the criss-cross method

Step 1- Identify the metal and non-metal Step 2- Write the symbols Step 3- write the charges Step 4- cross over the charges Step 5- remove the charge (+ -) Step 6- simplify the numbers and get rid of 1’s

NOTE: THE OVERALL CHARGE ON IONIC FORMULAS SHOULD ALWAYS EQUAL ZERO!!!!!!

Ionic Formulas Chemical formula – indicates the number and

type of atoms in a substance. H2O

2 hydrogen atoms + 1 oxygen atom NaNO3

1 sodium ion + 1 nitrogen atom + 3 oxygen atoms Formula unit – lowest whole-number ratio of ions

in a compound. The formula unit for table salt is NaCl. 1 unit of Na+ ions per 1 unit of Cl- ions. Formula does not show the charges of the ions.

Ionic Formulas What salt forms when aluminum combines with

chlorine? Aluminum has 3 valence electrons.

Loses 3 e- to reach octet. Forms Al+3 ion.

Chlorine has 7 valence electrions. Gains 1 e- to reach octet. Forms Cl-1 ion.

If the compound is neutral, it will take 1 Al+3 ion for every 3 Cl-1 ions.

The formula is AlCl3.

Aluminum + Chlorine

Al ClCl

Cl

Ionic Bonds – Writing FormulasIonic Bonds – Writing Formulas CRISS-CROSS METHOD

Oxidation numbers (excluding charge) of each ion trade places to become the subscripts in the formula – must be reduced to lowest whole number ratio; 1’s are not written

Ca & S

Ca2S2

Al & Cl

AlCl3

3+ 1- 2+ 2-

CaS

Writing Ionic Formulas Criss-Cross Method of writing ionic

formulas: Criss-cross charges to become subscripts Drop the charges when crossing over.

Example: What salt is formed from sodium and sulfur? Na forms +1 ions. S forms -2 ions. Na+1 + S-2 Na2S

Writing Ionic Formulas sodium + chlorine calcium + bromine lithium + oxygen aluminum + oxygen magnesium + nitrogen

Na+1 + Cl-1 Ca+2 + Br -1 Li+1 + O-2 Al+3 + O-2 Mg+2 + N-3

NaCl

CaBr2

Li2O

Al2O3

Mg3N2

Writing Ionic Formulas If the subscripts can be reduced, do so.

Example: calcium + oxygen Ions: Ca+2 + O-2

Wrong: Ca2O2

Right: CaO Example: lead + oxygen

Ions: Pb+4 + O-2

Wrong: Pb2O4

Right: PbO2

Ionic Bonds – Writing FormulasIonic Bonds – Writing Formulas

Sodium and chlorine bond in a 1:1 ratio to form NaCl

Calcium and chlorine bond in a 1:2 ratio for form CaCl2

What determines each ratio & formula? ________________

oxidation numbers

Ionic Bonds – Writing FormulasIonic Bonds – Writing Formulas

Ions Oxidation Numbers Ratio Formula

Magnesium & Oxygen Mg2+ & O2- 1:1 MgO

Lithium &

Sulfur

Aluminum & Oxygen

Sodium & Phosphorus

Barium &

Fluorine

Try to predict the ratio and resulting formula for each of the following ions based on their oxidation numbers:

Li+ & S2- 2:1 Li2S

Al3+ & O2- 2:3 Al2O3

Na+ & P3- 3:1 Na3P

Ba2+ & F- 1:2 BaF2

We will learn how to write nomenclature for: Ternary Salts

3 or more elements Includes a polyatomic ion

Salts with Multiple Oxidation Numbers Can be binary or ternary Includes a transition metal

Polyatomic Ions Polyatomic Ions – ions made of more than one

atom. Examples:

NO3-1

1 nitrogen atom and 3 oxygen atoms that collectively have a -1 charge.

SO4-2

1 sulfur atom and 4 oxygen atoms that collectively have a -2 charge.

PO4-3

1 phosphorus atom and 4 oxygen atoms that collectively have a -3 charge.

NH4+1

1 nitrogen atom and 4 hydrogen atoms that collectively have a +1 charge.

Polyatomic Ions in Salts Treat them like single-atom ions.

But do not change their formula!

If you need more than one of a particular polyatomic ion, use parentheses. Example:

Na+1 + NO3-1 NaNO3

Mg+2 + NO3-1 Mg(NO3)2

Al+3 + NO3-1 Al(NO3)3

Polyatomic Ions in Salts K+1 + OH-1 Ca+2 + OH-1 Ga+3 + OH-1 NH4

+1 + Cl-1 NH4

+1 + S-2 NH4

+1 + P-3 NH4

+1 + SO4-2

KOH

Ca(OH)2

Ga(OH)3

NH4Cl

(NH4)2S

(NH4)3P

(NH4)2SO4

Polyatomic IonsPolyatomic IonsName Formula

acetate C2H3O2- or

CH3COO-

ammonium NH4+

carbonate CO32-

chlorate ClO3-

chlorite ClO2-

chromate CrO42-

cyanide CN-

dichromate Cr2O72-

hydrogen carbonate HCO3-

hydroxide OH-

hypochlorite ClO-

nitrate NO3-

nitrite NO2-

perchlorate ClO4-

permanganate MnO4-

phosphate PO43-

sulfate SO42-

sulfite SO32-

Some ions contain more than one element - called a polyatomic ion

The group as a whole has an overall charge

Examples: Lithium and sulfate would

bond together to make Li2SO4

Ammonium and sulfur would bond together to make (NH4)2S

Ternary Salt NamingTernary Salt Naming Contains 3 or more elements: cation & anion – most polyatomic

ions are anions, only cation is ammonium (NH4+)

Naming: Name the cation (no changes) Name the anion (no changes)

Example: Na2SO4 = sodium sulfate Exception: When ammonium is paired with an element anion

NH4Cl = ammonium chloride

Ternary Salt FormulasTernary Salt Formulas You must use parentheses if you have more

than one polyatomic ion. Be sure to criss-cross the oxidation numbers and write it OUTSIDE of the parentheses.

K & PO4

K3PO4

Al & SO3

Al2(SO3)3

3+ 2- + 3-

Ternary Salt Formulas & NamingTernary Salt Formulas & Naming

IonsOxidation Numbers

Ratio Formula Name

Potassium & Hydroxide K+ & OH- 1:1 KOH

potassium hydroxide

Calcium & Carbonate

Barium &

Nitrate

Sodium & Phosphate

Ammonium & Sulfur

Try to predict the formulas and names for each ternary salt:

Ca2+ & CO32- 1:1 CaCO3

calcium carbonate

Ba2+ & NO3- 2:1 Ba(NO3)2

barium nitrate

Na3PO4Na+ & PO43- 1:3 sodium

phosphate

NH4+ & S2- 1:2 (NH4)2S

ammonium sulfide

Salts with Multiple Oxidation #s NamingSalts with Multiple Oxidation #s Naming

Transition elements can form more than one type of positive ion. For example, copper can form both Cu+ and Cu2+ ions,

and iron can form both Fe2+ and Fe3+ ions. Zinc and silver are two exceptions – they only have one

oxidation number The zinc ion is Zn2+ and the silver ion is Ag+.

Salts with Multiple Oxidation #s NamingSalts with Multiple Oxidation #s Naming

Transition elements can form more than one type of positive ion.

Naming: Name the cation Put the roman numeral representing the oxidation # of the

metal in parentheses (do not indicate the charge) Name the anion, changing the ending to “ide” (binary) or

naming the polyatomic ion (ternary) Example:

FeCl2 = iron (II) chloride FeCl3 = iron (III) chloride

Salts with Multiple Oxidation Salts with Multiple Oxidation Numbers PracticeNumbers Practice

IonsOxidation Numbers

Ratio Formula Name

Copper & Nitrate

Cu+ & NO3- 1:1 CuNO3

copper (I) nitrate

Lead &

Oxygen

Cobalt &

Hydroxide

Nickel & Phosphate

Chromium & Sulfur

Pb4+ & O2- 2:1 PbO2lead (IV)

oxide

Co3+ & OH- 3:1 Co(OH)3cobalt (III) hydroxide

Ni2+ & PO43- 2:3 Ni3(PO4)2

nickel (II) phosphate

Cr2+ & S2- 1:1 CrS chromium (II) sulfide