Ionic Compounds

Elements vs. Compounds• Elements are composed of one type of

atom

• Elements are represented by a symbol which consists of only 1 capital letter

C

Au

Chlorine

Sodium

carbon

gold

Cl

Na

• Compounds are composed of two or more elements.

• Compounds are represented by a formula which consists of 2 or more element symbols written next to each other.

• Usually the least electronegative element is first.

NaCl

NH4C2H3O2

1 sodium, 1 chloride

1 Nitrogen, 7 Hydrogen, 2 Carbon, 2 Oxygen

Objective 5 and 6

Reading the Composition of a Formula

CO

CO2

CoBr2

(NH4)3PO4

1 carbon, 1 oxygen

1 carbon, 2 oxygen

1 cobalt, 2 bromine

3 nitrogen, 12 hydrogen, 1 phosphorus, 4 oxygen

Ionic Compounds

Contain a positive ion (cation) and a negative ion (anion).

Usually a metal and a nonmetal, or may contain a polyatomic ion.

Objectives 1 and 3

Objective 1

Molecular compounds

Compounds composed of ONLY nonmetals.

Do not contain ions.

Will be dealt with in the next unit.

N2O4 H2O2 C6H12O6

Objective 2

Formula Units

The lowest ratio of elements in a compound.

Also known as the empirical formula.

Written for ionic compounds. (they form crystals)

Empirical vs Molecular formulas

• Empirical formulas show the elements in the lowest ratio possible.

NO2 HO CH2O AlBr3

• Molecular formula state the actual number of each atom present.

N2O4 H2O2 C6H12O6 AlBr3

Ionic compounds

• Ionic compounds are always written as empirical formulas. They represent a formula unit for the ionic crystal.

CaCl2 Fe2O3 AgNO3

Law of Definite Proportions

• In a particular compound the masses of an element are always in the same proportions.

CO2 is carbon dioxide

CO is a different ratio and so a different compound called carbon monoxide

Formation of ions

• Octet Rule – in forming compounds atoms will try to obtain a noble gas electron configuration.

• To do this metals ________ electrons and nonmetals _________ electronsgain

lose

Metal Examples

Na atom = 1s22s22p63s1 Na

Na1+ = 1s22s22p6 Na1+

Note the 3rd energy level electron was lost to have the same electron configuration as neonNe = 1s22s22p6

.

You try

Ca =

Ca2+ =

What noble gas does Ca2+ resemble?

1s22s22p63s23p64s2

1s22s22p63s23p6

The oxidation number on the metal ion (cation) is the positive value of how many electrons were lost.

:Ca

Ca2+

x

Naming metal ions

• Metal ions names stay the same as their element name EXCEPT if the metal has more than one oxidation number.

(Look on your Elements and Ions to Know handout to find multiple oxidation numbers)

Naming metal ions

If there is more than one oxidation number write the name of the element followed by its oxidation number written in Roman numerals and placed in parenthesis.

Ex. Fe+2 Iron (II)/Ferrous Fe+3 Iron (III)/FerricCu+1 Copper (I)/CuprousCu+2 Copper (II)/Cupric

Examples

• Mg2+

• Fe3+

• Al3+

• Fe2+

• Tin (IV)• Copper (I)• Silver

Magnesium ion

Iron (III) ionAluminum ionIron (II) ion

Sn4+

Cu1+

Ag1+

Nonmetals

• Cl atom = 1s22s22p63s23p5 :Cl:

• Cl1- = 1s22s22p63s23p6 :Cl:1-

Note the 3rd energy level electron was lost to have the same electron configuration as argonAr = 1s22s22p63s23p6

...

..

..

You try

O =

O2- =

What noble gas does O2- resemble?

1s22s22p4

1s22s22p6

The oxidation number on the nonmetal ion (anion) is the negative value of how many electrons were gained to obtain a noble gas structure.

:O. .

..

..

..

:O:2-

Naming nonmetal ions

• If the ion is composed of one element:

name the element but change its

ending to “ide”.

• If the ion is composed of two or more elements:name the polyatomic ion (either memorized or

looked up on a polyatomic ion chart.)

Naming nonmetal monoatomic ionsend in “-ide”

• Cl1-

• S2-

• F1-

• O2-

Chloride ion

Sulfide ion

Oxide ion

Fluoride ion

Notice how close the spellings are, SPELLING COUNTS!!!!

Naming nonmetal polyatomic ionsmost end in “-ate”, “-ite”

• Sulfate ion

• Hydroxide ion

• Sulfite ion

• Nitrate ion

• Acetate ion

SO42-

OH1-

SO32-

NO31-

C2H3O21-

Notice how close the spellings are, SPELLING COUNTS!!!!

Ionic Bonds – The achievement of the "noble gas configuration" by electron transfer from metallic atoms to non-metallic atoms. The electrostatic bond is formed between positively charged metallic ions (cations) and negatively charged non-metallic ions (anions).

LINK

LINK

NaCltable salt

Crystal Formation

Ionic Bonds: MgO (magnesium oxide)

Mg atom, r = 1.6Å

LINK

O atom, r = 0.78Å

- 2 e-

+ 2 e-

Mg2+ ion, r = 0.6Å

O2- ion, r = 1.32Å

Writing Formulas

• The total of the charges must be zero. • Subscripts multiplied by the cation charge

are added to the subscript multipled by the anion charge to total zero.

• Ca2+ Br1- CaBr2 1(2+) + 2(1-) = 0 where the underlined numbers become the subscripts.

Writing Formulas Cont.

• (NH4)1+ S2- (NH4)2S 2(1+) + 1(2-) = 0 where the

underlined numbers become the subscripts.

• Ba2+ (PO4)3- Ba3(PO4)2 3(2+) + 2(3-) = 0 where the

underlined numbers become the subscripts.

Naming Ionic Compounds

• Name the metal ion – remember to use roman numerals if there is more than one possible oxidation number

• Name the nonmetal or polyatomic ion

• Example: ZnCl2

KOH

Zinc chloride

Potassium hydroxide

||

More than one oxidation state

• The oxidation number must be found for the metal.

• Remember all compounds are electrically neutral. (cation charge + anion charge = 0)

CuCl2 1(Cux) + 2 (Cl1-) 1x + 2(-1) =0

x= 2

Copper (II) chloride

NiS 1(Nix) + 1(S2-) 1(X) + 1(-2) =0

x = 2

Nickel (II) Sulfide

Sn(SO4)2 1(Snx) + 2(SO42-) 1(x) + 2(-2) = 0 x = 4

Tin (IV) sulfate

Special Ionics: Acids

Generally Acids have formulas that begin with H (hydrogen)

HCl(aq) H3PO4(aq) H2CO3(aq)

H2SO4(aq) HF(aq) HBr(aq)

Notice they all have (aq) written beside the formulas, this indicates they are dissolved in water or aqueous.

Naming 2 Element Acids

Remember this is for acids with: hydrogen and one other element

Such as HCl

1. Start the name with hydro2. Finish with the nonmetal changing its

ending to “ic”Ex. HCl = hydrochloric acid

Naming Acids with Polyatomic Ions

Name the polyatomic ion in the acid (look up on a polyatomic ion sheet if you need to)

If the polyatomic ion ends in “ate” change the ending to “ic”

Ex. H2CO3 polyatomic ion = carbonatechange to =add =

Final name:

carbonic

Carbonic acidacid

If the polyatomic ion ends in “ite” change the ending to “ous”

Example:

HNO2 polyatomic ion = nitritechange to =add =

Final name:

nitrousacid

nitrous acid

Careful of odd ones:

• Sulfate turns to sulfuric

• Sulfite turns to sulfurous

• Phosphate turns to phosphoric

• Phosphite turns to phosphorous

Writing Acid Formulas

• ALWAYS start with H

• Decide what the anion is.

remember: if it starts with hydro, look for a nonmetal element and find its oxidation number.

Example: hydrobromic acid

H+1Bromic sounds like bromine

Bromine has a -1 charge so..,

Br1-

HBr(aq)

If it has no prefix but ends in “ic” look for a polyatomic ion that has the same root word but ends in “ate”.

Find the polyatomic ions formula and charge

Example: chromic acid

Polyatomic ion: chromate - CrO42-

Ions involved: H1+ CrO42-

Formula: H2CrO4(aq)

•

If it has no prefix but ends in “ous” look for a polyatomic ion that has the same root word but ends in “ite”.

Find the polyatomic ions formula and charge

Example: sulfurous acid

Polyatomic ion: sulfite - SO32-

Ions involved: H1+ SO32-

Formula: H2SO3(aq)

Acid Review

• Acids have two names Hydrogen Bromide or Hydrobromic Acid. Hydrogen nitrate or Nitric Acid.

• Binary acids are formed from hydrogen and one other element. They are named Hydro-element-ic Acid.

• Polyatomic Ions attached to hydrogens change their endings. --ate becomes –ic and –ite becomes –ous. HNO3 is hydrogen nitrate so it becomes Nitric acid.

Properties of Ionic Compounds• The strong attractions between the cations and

the anions in ionic solids are responsible for their high melting points. For ionic compounds, melting points typically range from 300oC to 1000oC.

• Ionic compounds are soluble in water. • In aqueous solution, an ionic compound

dissociates into its ions. • This means that when NaCl is dissolved in water,

the solution contains Na+ ions and Cl- ions. • The dissociated ions in aqueous solution gives

the solution the ability to conduct electricity. Therefore, ionic compounds dissolved in water makes strong electrolytes.

Metallic Solid• Infinite array of atoms held together by

metallic bonding• Metallic bonding is like positive metal ions

in a sea of freely-moving negative electrons• Metallic bonding is moderate to strong• Properties:

– moderate-to-high melting point, boiling point

– may be hard or soft– electrically conductive

solid and liquid– malleable, ductile– lustrous