Chemistry II

Ionic CompoundsNaming and Writing Formulas

Review of how ions are formed

• Octet rule – elements are most stable when they have 8 valence electrons

• Elements can gain or lose valence electrons in order to have 8.

Formation of Cation

11p+

sodium atomNa

e-

loss of one valence electron

e-

e-

e-

e-e-

e-

e-

e- e-

e-

sodium ionNa+

11p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-e-

Formation of Anion

17p+

chlorine atomCl

e-

e-

e-

e-

e-e-

e-

e-

e- e-

e-

e-

e-

e-

e-

e-

e-

e-

gain of one valence electron

chloride ionCl1-

17p+e-

e-

e-

e-e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

Bonding

• Chemical Bond– attractive force between atoms or ions that binds

them together as a unit

– Purpose bonds formFORM IN ORDER TO ….1. To decrease potential energy (PE)

2. To Increase stability

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Why bonds form…

• Atoms of many elements are more stable as they are bonded to other atoms.

• Energy is released into surroundings resulting in a system with lower energy.

• An atom’s electron configuration determines how it interacts with other atoms

• Particularly valence electrons

• Chemical interactions(attractions) between charged particles - Called Electrostatic attraction

• Result from a transfer of electrons making a cation and anion

What are ionic bonds?

Crystal Lattice NaCl 1:1 Ratio

.

Ionic compounds do not exist as single molecules but rather as numerous units organized in a stable crystal

• Ionic bonds form between metals and non-metals

– Metals have lower ionization energies and therefore more readily “give away” electrons – Form Cations

– Non-metals have high electron affinities and therefore more readily accept electrons. – Form Anions

– New Term- Oxidation Number = ion charge– sodium’s oxidation number is 1+, Chlorine’s is 1-

Participants

• Cation – borrows name from element– Always listed first

• Anion – ends in “ide” (with the exception of polyatomic ions)– Always listed second

• Examples– NaCl – sodium chloride– ZnS – zinc sulfide– Mg3N2 – magnesium nitride

• SPELLING COUNTS!

Naming Ionic Compounds

Example: Aluminum Chloride

Step 1:

Step 2:1 3

Step 3: AlCl3

Writing Ionic FormulasCriss-Cross Rule

Al Cl

Al Cl

3+ 1-Write symbols & charge of elements.Write charges ABOVE the letters

criss-cross charges as subscripts

combine as formula unit*“1” is never shown

*get rid of charges on top

Step 4 : *simplify if needed

Variable Charge Ions

• Some elements in the transition metals can form more than one type of ion. Sometimes they may lose 2, 3, 4 or even more electrons in order to bond with another element.

• So these metals can form +2, +3 ,+4 etc cations in one compound but have a different charge in another compound. In order to tell them apart we name them differently.

Writing the formula

• When given the name of the compound, the Roman numeral after the metal tells us the CHARGE of the metal.

• Copper II Chloride – means Cu+2 Cl-1

• Follow the same steps as before >>>>1. Write out the charges2. Criss-cross3. Combine as a formula unit (get rid of charges on top) 4. Simplify if needed

iron oxide

A. To name, given the formula:

1. Figure out charge on cation.2. Write name of cation.

3. Write Roman numerals in ( ) to show cation’s charge.

4. Write name of anion.

FeO

Fe2O3

CuBr

CuBr2

iron oxide

CuFe

Stock Systemof nomenclature

Fe? O2– iron (II) oxide

Fe? O2– iron (III) oxide

copper bromide

copper bromide

Cu? Br1– copper (I) bromide

Cu2+ Br1– copper (II) bromide

Fe?

Br1–

O2– O2–

Fe2+

Fe3+ Fe3+

Cu1+

Cu?

• When writing the formula for an ionic compound with a polyatomic ion, follow the same rules but treat the polyatomic ion as a single unit.

(NH4)3N

Fe2(Cr2O7)3

Sn(SO4)2

NH4ClO3

Mg(NO2)2

BaSO4

Writing Formulas w/Polyatomic Ions

Polyatomic Ion: a group of atoms that stay together and have a single, overall charge.

Ba2+ and SO4

2–

Mg2+ and NO2

1–

NH41+ and ClO3

1–

Sn4+ and SO42–

Fe3+ and Cr2O72–

NH41+ and N3–

barium sulfate

magnesium nitrite

ammonium chlorate

tin (IV) sulfate

iron (III) dichromate

ammonium nitride

?

Rules for ParenthesesParentheses are used only when the following two condition are met:

1.There is a (polyatomic ion) present and…2.There are two or more of that in the formula.

Examples:

NaNO3 NO31- , but there is only one of it.

Co(NO3)2 NO31- there are two of them

(NH4)2SO4 NH41+ there are two of them;

SO42- there is only one of it.

Co(OH)2 OH1- there are two of it. Al2(CO3)3 CO3

2- there are three of them. NaOH OH1- there is only one of it.

Pattern to Memorizing Nomenclature

XY“-ide”

XYO3“-ate”

XYO2“-ite”

XYO“hypo___-ite”

XYO4“per___-ate”

normal 1 less oxygen 2 less oxygen1 more oxygen

• Physical characteristics result from the strong attractive forces between charged particles and the crystal structure– High melting and boiling points

• Lots of energy necessary to break strong bonds

– Solid at room temperature• Stable crystal structure

– Hard and brittle• Crystal allows compound to withstand great force• Too much force causes repulsive forces to overpower

attractive forces and the crystal shatters

– Conduct electricity when melted and dissolved in water

• Charged particles that are able to move

Physical Characteristics