Naming Compounds and Writing Formulas

Step 1 - Determine the Bond TypeMetal atoms Non-metal atoms

Metallic bonds Ionic bonds Covalent bonds

Ionic bonds – Form between metal and a non-metal atoms. Forms ions, not molecules. Covalent bonds – Form between 2 non-metals. Forms molecules.

Metallic bonds – Mixture of 2 metal atoms.

Naming Ionic Compounds

1. Name the first ion2. Name the second ion changing the suffix to

–ide.

Examples:NaCl Sodium Chloride

CalciumCaCl2Chloride

MgI2Magnesium iodide

Practice

KF

MgI2

AlCl3

GaF3

potassium fluoride

magnesium iodide

gallium fluoride

aluminum chloride

Writing Ionic FormulasTwo simple steps:1. Write the symbol and charge of each ion2. Balance the charges using subscripts.

– What is the number of valence electrons?– What is the charge on the ION?

Magnesium chloride

Mg+2 Cl-1

Cl-1

MgCl2

Write the symbol and charge of each ion.Balance the charges by supplying subscripts. Subscripts tell how many of each atom is present.You need a second Cl-1 to balance the charges

Aluminum Sulfide Write the symbol and charge of each ion.Al+3 S-2

Balance the charges by supplying subscripts.In this case the charges do not evenly divide into each other. You must find the least common multiple. SIX

How many aluminums are needed to arrive at a +6 charge?

How many sulfurs are needed to arrive at a -6 charge?

2

3

Al+3 S-2

S-2

Al2S3

Practice

magnesium oxide

lithium bromide

aluminum chloride

sodium oxide

MgO

LiBr

AlCl3

Na2O

Polyatomic ions

• Polyatomic ion – Group of atoms that act as a unit and carry a charge.

CO3-2

carbonate

This ion is composed of one carbon and three oxygens and the entire group has a charge of -2.

Some Polyatomic Ions

SO4-2 Sulfate

SO3-2 Sulfite

ClO4-1 Perchlorate

ClO3-1 Chlorate

ClO2-1 Chlorite

ClO-1 Hypochlorite

PO4-3 Phosphate

C2H3O2-1 Acetate

OH-1 Hydroxide NO3

-1 Nitrate

NO2-1 Nitrite

You need to recognize these!!!

NH4+1 Ammonium

(only positive PI)

More examples:

How to Name Ionic Compounds with Polyatomic Ions

1. Name the first ion.2. Name the polyatomic

ion. – You just have to look

up the polyatomic ion on your sheet.

Na2CO3

Sodium carbonate

When you look at this compound you should recognize that this is NOT binary. There are THREE elements present. When you see this, immediately look for a polyatomic ion. CarbonateCarbonate is present here.

NH4Cl Name the first ion.

Ammonium Name the second ion.chloride

Notice that since the second ion is a nonmetal, the suffix changes to –ide.

(NH4)3PO4Name the first ion.

Name the second ion.Ammonium phosphate

Looks like a monster, but it’s really a pussycat.

How do you write formulas for ionic compounds with polyatomic ions?

Very much like writing formulas for Binary Ionic Compounds.

Two steps:

•Write the formulas/symbols of each ion.

•Balance the charges by using subscripts.

•If a subscript is needed for a polyatomic ion, it must be put in parentheses with the subscript on the outside.

Let’s do some!!

Aluminum nitrate First, you can tell from the name that there is a polyatomic ion present (nitrate). All binary ionic compounds have suffixes of –ide.

Write the formula/symbol and charge of each ion.

Al+3 NO3-1

Balance the charges by supplying subscripts.

Since Al is +3 and NO3 is -1, you need a total of 3NO3

-1 to balance one Al+3

Since you will need a subscript of 3 for NO3-1, you

need to put this in parentheses with the 3 outside.

Al(NO3)3

Silicon acetate Write the formula/symbol and charge of each ion.Si+4 C2H3O2

-1

Balance the charges by supplying subscripts. Since Si is +4 and C2H3O2 is -1, you will need 4 C2H3O2

-

1 to balance 1Si+4

Si(C2H3O2)4

Calcium phosphateWrite the formula/symbol and charge of each ion.

Balance the charges by supplying subscripts. Since Ca is +2 and PO4 is -3, you will need 3 Ca+2 to balance 2 PO4

-3

Ca+2 PO4-3

Ca3(PO4)2

Covalent Compounds

What are Binary Molecular Compounds?

• These compounds contain two elements (binary).

• The term “molecular” indicates that these elements are joined by a covalent bond.

• They must therefore be nonmetals.

• Bottom line – 2 elements – both nonmetals

• To name and write formulas for these, you must know some numerical prefixes.

Naming Covalent Compounds – you must use prefixes.

1 = mono 3 = tri 5 = penta 7 = hepta 9 = nona

2 = di 4 = tetra 6 = hexa 8 = octa 10 = deca

1.The first nonmetal only gets a numeric prefix when there is more than one. No prefix if there is only one.

2.The second element always gets a numeric prefix and always has a suffix of -ide

CO2

Carbon dioxide

CO

Carbon monoxide

N2O4

Dinitrogen tetraoxide

H2O

Dihydrogen monoxide

CCl4

Carbon tetrachloride

Name the first element. Since there is only one, no prefix is needed. The second element always gets a prefix and a suffix of –ide.

Name the first element. Since there are two present, the prefix “di” is needed. The second element always gets a prefix and a suffix of –ide.

Do you think it wise to BAN DHMO?

AlCl3What do you think about this one???

Be careful. This is a metal and nonmetal.

Always keep your Periodic Table in front of you for reference.

You may have been tempted to say “aluminum trichloride”. This is INCORRECT!

This is a binary IONIC compound. No prefixes are used. Simply aluminum chloride.

Given the names of binary molecular compounds, how do you write the formulas?

Very easy to do!!! The prefixes tell you how to write the formulas. DO NOT CONSIDER CHARGES. NONMETALS ARE ALL NEGATIVE SO TO USE CHARGES DOES NOT WORK!

Silicon dioxide

Diphosphorous pentachloride

Silicon and oxygen are both nonmetals.

The lack of a prefix on silicon means that there is only ONE silicon.

The prefix “di” in front of oxide means that there are TWO oxygens.

SiO2

Phosphorous and chloride are both nonmetals.

The prefix “di” means that there are TWO phosphorouses (Is that a word?)

The prefix “penta” before chlorine means that there are five chlorines.

P2Cl5

NO

Nitrogen monoxide Nitrogen and oxygen are both nonmetals.

The lack of a prefix on nitrogen means only ONE nitrogen.

The prefix “mono” on oxygen indicates ONE oxygen.

Isn’t this sooooooo easy!??

Name the following compounds.

PH3

CO

HI

N2O3

phosphorous trihydride

carbon monoxide

hydrogen monoiodide

dinitrogen trioxide