JOURNAL 24 Why is it important for chemist to

know chemical names and formulas?

What is the difference between an Ionic and Covalent bond?

TODAY WE WILL DETERMINE THE FORMULA OF AN IONIC COMPOUND FORMED BETWEEN TWO GIVEN IONS

SIGNIFICANCE OF A CHEMICAL FORMULA Chemical formula- indicates the relative

number of atoms of each kind of chemical compounds.

Example C8H18

Subscript- indicates that there are 8 carbon atoms in a

molecule of octane Indicates that there are 19 hydrogen atoms in a

molecule of octane Unlike a molecular compound, an ionic

compound consists of lattice of positive and negative ions held together by mutual attraction.

Al2(SO4)3 Note how the parenthesis is used. They surround the polyatomic anion to

identify it as a unit. The subscript 3 refers to the entire

unit. When there is no subscript next to an

atom’s symbol, the value of the subscript is one.

A CHEMICAL FORMULA

MONATOMIC IONS Ions formed from a single atoms are known as

monatomic ions. By gaining or losing electrons, many elements form

ions with noble-gas configurations. Examples

Group 1 metals lose one electron to give 1+ cationsNa+

Group 2 metals lose two electrons to give 2+ cationsMg 2+

Nonmetals of groups 15-17 gain electronsN3-S2-

NAMING MONATOMIC IONSMonatomic cations are identified by the

elements nameMonatomic anions

Ending of the name is dropped-ide is added to the root name

Examples: chloride, sulfide, fluorideElements with multiple ions

Examples:Iron (II), Iron (III), Cobalt (II), Cobalt (III)Copper (I) Copper (II)

BINARY IONIC COMPOUNDS Binary compounds- compounds

composed of 2 elements The total number of positive charges

must equal the number of negative chargesExamples: Mg and Br,

As an aid to determining subscripts in formulas for ionic compounds, the positive and negative charges can cross – over.Example: Al (3+) and O (2-) Al2O3

NAMING BINARY IONIC COMPOUNDS The name of the cation is given first followed

by the anion. Examples

Al2O3 Aluminum Oxide

CaBr2

BaO

YOUR TURN TO PRACTICE

CAN YOU WRITE THE FORMULA WHEN GIVEN THE NAME? Barium oxide Potassium chloride Strontium bromide Lithium sulfide

YOUR TURN TO PRACTICE

STOCK SYSTEM OF NOMENCLATURE

Some elements have 2 or more cations (with different charges)Examples: Iron, Copper

Use Roman numeral to indicate the ion’s charge

The numeral is in parentheses and placed right after the metal name

Fe2+ - Iron (II) Metals that form only one cation do

not include a roman numeral

PRACTICE Write the formula and give the name

for the compound formed by the ions Cr3+ and F-

Write the symbols for the ions side by side (cation first)

Cross over charges to give subscripts

Answer: Chromium (III) Flouride; the formula is CrF3

PRACTICE Write the formula and give the name

for the compound formed by the ions Cu2+ and Br-

Write the symbols for the ions side by side (cation first)

Cross over charges to give subscripts

Answer: Copper (II) Bromide; CuBr2

PRACTICE Write the formula and give the name

for the compound formed by the ions Fe2+ and O2-

Write the symbols for the ions side by side (cation first)

Cross over charges to give subscripts

Answer: Iron (II) oxide; FeO

PRACTICE Write the formula and give the name

for the compound formed by the ions Pb2+ and Cl-Write the symbols for the ions side by

side (cation first)Cross over charges to give subscripts

Answer: Lead (II) chloride; PbCl2

PRACTICE Write the formula and give the name

for the compound formed by the ions Hg2+ and S2-

Write the symbols for the ions side by side (cation first)

Cross over charges to give subscripts

Answer: Mercury (II) sulfide; HgS

PRACTICE Write the formula and give the name

for the compound formed by the ions Sn2+ and F-

Write the symbols for the ions side by side (cation first)

Cross over charges to give subscripts

Answer: Tin (II) fluoride; SnF2

PRACTICE Write the formula and give the name

for the compound formed by the ions Fe3+ and O2-

Write the symbols for the ions side by side (cation first)

Cross over charges to give subscripts

Answer: Iron (III) oxide; Fe2O3