naming compounds and writing formulas

Naming Compounds and

Writing Formulas

Periodic Table Recall that the periodic table is more

than a list of elements. Elements are put in columns because of

similar properties. Each column is called a group.

2A

1A

3A4A

5A6A

7A

0Representative Elements

The group A elements

Metals

Transition Metals

The Group B elements

Nonmetals

Metalloids

Systematic Naming There are too many compounds to

remember the names of them all. A compound is made of two or more

elements. The name should tell us how many and

what type of atoms.

Types of Compounds

There are two types of compounds: ionic compounds and molecular compounds.

Ionic Compounds

The simplest ratio of the ions represented in an ionic compound is called a formula unit.

The overall charge of any formula unit is zero.

In order to write a correct formula unit, one must know the charge of each ion.

Atoms and Ions Atoms are electrically neutral. They have the same number of protons

and electrons. Ions are atoms, or groups of atoms,

with a charge. Ions have a different numbers of

electrons.

Anions An anion is a negative ion. An anion has gained electrons. Nonmetals can gain electrons. The charge is written as a superscript

on the right.

F-1 Has gained one electron

O-2 Has gained two electrons

Cations A cation is a positive ion. It is formed by losing electrons. There are more protons than electrons. Metals form cations.

K1+ Has lost one electron

Ca2+ Has lost two electrons

Ionic Compounds

The charges of monatomic ions, or ions containing only one atom, can often be determined by referring to the periodic table or table of common ions based on group number.

The charge of a monatomic ion is equal to its oxidation number.

Charges on Ions For most of the Group A elements, the

Periodic Table can tell what kind of ion they will form from their location.

Elements in the same group have similar properties, including the charge when they are ions.

2+

1+

3+ 3- 2- 1-

Charges on Ions:Oxidation Numbers

Naming Cations

We will use the systematic way. For cations, if the charge is always the

same (Group A) just write the name of the metal.

Naming Cations Transition metals (as well as tin and

lead) can have more than one type of charge.

Indicate the charge with Roman numerals in parenthesis.

Zinc (Zn2+) and silver (Ag1+), although transition metals, only have one possible charge. Roman numerals ARE NOT used for zinc and silver.

Example Li1+

Li is the symbol for lithium.

Lithium is a Group 1A metal, so the charge is always the same. Write the name of the metal.

Li1+ is called the Lithium ion.

Example Sr2+

Sr is the symbol for strontium.

Strontium is a Group 2A metal, so the charge is always the same. Write the name of the metal.

Sr2+ is called the Strontium ion.

Example Fe2+

Fe is the symbol for iron.

Iron is a transition metal, so the charge is not always the same. Write the name of the metal, indicating the charge with Roman numerals in parenthesis.

Fe2+ is called the Iron (II) ion.

Example Pb2+

Pb is the symbol for lead.

Lead is a Group 4A metal, and the charge is not always the same. Write the name of the metal, indicating the charge with Roman numerals in parenthesis.

Pb2+ is called the Lead (II) ion.

Problem Name the following cations.

Ca2+

Sn4+

Calcium ion

Al3+ Aluminum ion

Tin (IV) ion

Problem Name the following ions.

Na1+

Cu1+

Sodium ion

Fe3+ Iron (III) ion

Copper (I) ion

Writing the Formulas for Cations

Write the formula for the metal. If a Roman numeral is in parenthesis

use that number for the charge. Indicate the charge with a superscript.

Writing the Formulas for Cations

If no Roman numeral is given, find the Group A metal on the periodic table and determine the charge from the column number.

Example Nickel (II) ion

Ni is the symbol for nickel.

Nickel is a transition metal, which is the reason why the charge with Roman numerals in parenthesis was included.

The formula for the nickel (II) ion is

Ni2+.

Example Gallium ion

Ga is the symbol for gallium.

Gallium is a Group 3A metal and its charge is always the same (+3).

The formula for the gallium ion is

Ga3+.

Problem Write the formulas for the following

cations.

Copper (II) ion

Magnesium ion

Potassium ion

Mg2+

Cu2+

K1+

Problem Write the formulas for the following ions.

Chromium (VI) ion

Silver ion

Mercury (II) ion

Ag1+

Cr6+

Hg2+

Naming Anions Naming monatomic anions is always the

same. Change the element ending to – ide Example: F1- F is the symbol for fluorine, F1- is

ide.fluor ine.

Example Cl1-

Cl is the symbol for chlorine.

Chlorine is a Group 7A nonmetal, so the charge is always the same (-1).

Cl1- is called the chloride ion.

Example O2-

O is the symbol for oxygen.

Oxygen is a Group 6A nonmetal, so the charge is always the same (-2).

O2- is called the oxide ion.

Problem Name the following anions.

S2- sulfide ion

Br1- bromide ion

N3- nitride ion

Problem Name the following anions.

As3- arsenide ion

Te2- telluride ion

Writing the Formulas for Anions

Write the formula for the nonmetal. Find the Group A nonmetal on the

periodic table and determine the charge from the column number.

Problem Write the formulas for the following anions.

iodide ion I1-

phosphide ionP3-

Problem Write the formulas for the following anions.

selenide ion Se2-

carbide ion C4-

Ionic Compounds

Oxidation numbers can be used to determine the chemical formulas for ionic compounds.

If the oxidation number of each ion is multiplied by the number of that ion present in a formula unit, and then the results are added, the sum must be zero.

Ionic Compounds

In the formula for an ionic compound, the symbol of the cation is written before that of the anion.

Subscripts, or small numbers written to the lower right of the chemical symbols, show the numbers of ions of each type present in a formula unit.

Binary Ionic Compounds

Binary ionic compounds are composed of a metal bonded with a nonmetal.

Name the metal ion using a Roman numeral in parenthesis if necessary.

Follow this name with the name of the nonmetal ion.

Example

Name the following binary ionic compounds.

NaCl Sodium chloride

Ca3P2 Calcium phosphide

Example


CuO Copper (II) oxide

SnBr2 Tin (II) bromide

Problem


Fe2S3 Iron (III) sulfide

AlF3 Aluminum fluoride

Problem


KCl Potassium chloride

Na3N Sodium nitride

Problem


CrN Chromium (III) nitride

PbO2 Lead (IV) oxide

Writing Formulas for Binary Ionic Compounds

Write the symbol for the metal. Determine the oxidation number from either the column number or the Roman numeral and write it as a superscript to the right of the metal’s symbol.


To the right of the metal’s symbol, write the symbol for the nonmetal. Determine the oxidation number from the column number and write it as a superscript to the right of the nonmetal’s symbol.


Example: potassium fluoride

K1+

F1-


If the two oxidation numbers add together to get zero, the formula is a one-to-one ratio of the elements.


Example: potassium fluoride

K1+

F1-

KF


Example: aluminum sulfide

Al3+

S2-


If the two oxidation numbers DO NOT add together to get zero, you will need to “criss-cross” the superscripts. These numbers now become subscripts.



Al3+

S2-

3+2-


Omit all positive and negative signs and omit all 1’s.



Al S2 3

Al2S3

Problem

Lithium selenide

Write the formulas for the following binary ionic compounds.

Tin (II) oxide

Li2Se

SnO

Problem

Tin (IV) oxide


Magnesium fluoride

SnO2

MgF2

Problem

Copper (II) sulfide


Iron (II) phosphide

CuS

Fe3P2

Problem

Gallium nitride


Iron (III) sulfide

GaN

Fe2S3

Ternary Ionic Compounds

Ternary ionic compounds are composed of at least 3 elements.

Name the metal ion, using a Roman numeral in parenthesis if necessary.

Follow this name with the name of the polyatomic ion.

Polyatomic ions Polyatomic ions are groups of atoms

that stay together and have a charge. Examples are on page 7 of the

Reference Tables for Chemistry and include:Nitrate NO3

-1

Nitrite NO2-1

Hydroxide OH-1


There is one polyatomic ion with a positive oxidation number (NH4

+) that

may come first in a compound. Name the ion.

Follow this name with the name of the anion or second polyatomic ion.


Certain polyatomic ions, called oxyanions, contain oxygen and another element.

Examples Name the following ternary ionic

compounds.LiCN

Fe(OH)3

Lithium cyanide

Iron (III) hydroxide

Examples Name the following ternary ionic

compounds. (NH4)2CO3 Ammonium carbonate

NiPO4 Nickel (III) phosphate

Problems Name the following ternary ionic

compounds.NaNO3 Sodium nitrate

CaSO4 Calcium sulfate

Problems Name the following ternary ionic

compounds.

(NH4)2O Ammonium oxide

CuSO3 Copper (II) sulfite

Writing Formulas for Ternary Ionic Compounds

Write the symbol for the metal or ammonium ion. Write the oxidation number as a superscript to the right of the metal’s/ammonium ion’s symbol.


To the right of the metal’s symbol, write the symbol for the nonmetal or polyatomic ion. Write the oxidation number as a superscript to the right of the nonmetal’s/polyatomic ion’s symbol.


Example: potassium nitrate

K1+

NO3

1-


If the two oxidation numbers add together to get zero, the formula is a one-to-one ratio of the elements.


Example: potassium nitrate

K1+

NO3

1-KNO3


Example: aluminum hydrogen sulfate

Al3+

HSO4

1-


If the two oxidation numbers DO NOT add together to get zero, you will need to “criss-cross” the superscripts. These numbers now become subscripts.

Parentheses are to be placed around polyatomic ions before criss-crossing.



Al3+

HSO4

1-

3+1-( )


Omit all positive and negative signs and omit all 1’s.



Al(HSO4) 3Al(HSO4)3

Problems Write the formulas for the following

ternary ionic compounds.Ammonium chloride

Ammonium sulfide

NH4Cl

(NH4)2S


ternary ionic compounds.Barium nitrate

Zinc iodate

Ba(NO3)2

Zn(IO3)2


ternary ionic compounds.Sodium hypochlorite

Chromium (III) acetate

NaClO

Cr(CH3COO)3


ternary ionic compounds. Iron (II) dichromate

Mercury (I) bromate

FeCr2O7

HgBrO3

STOP HERE

Molecular Compounds

Writing Names and Formulas

Molecular Compounds

Molecular compounds are made of molecules.

They are made by joining nonmetal atoms together into molecules.

Naming is Easier

A molecular compound’s name tells you the number of atoms through the use of prefixes.

Prefixes

1 mono- 2 di- 3 tri- 4 tetra- 5 penta-

6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca-

Prefixes

The name will consist of two words.

Prefix name prefix name -ide

One exception is we don’t write mono- if there is only one of the first element.

Prefixes

The following double vowels cannot be used when writing names: (oa) (oo)

Example

NO2

There is one nitrogen

mononitrogen

But, you cannot use mono- on the first element, so drop the prefix.

mononitrogen nitrogen

Example

NO2

There are two oxygens

dioxygen

Example

NO2

dioxygen

You need the suffix -ide

dioxygenide

Example

NO2

nitrogen dioxide

Example

N2O

There are two nitrogens

dinitrogen

There is one oxygen

monooxygen

Example

N2O

monooxygen

You cannot run (oo) together, so

monoxygen

Example

N2O

monoxygen

You need the suffix -ide

monoxygenide

Example

N2O

dinitrogen monoxide

Problem

Name the following molecular compounds.

Cl2O7

CBr4

dichlorine heptoxide

carbon tetrabromide

Problem

Name the following molecular compounds.

CO2

BCl3

carbon dioxide

boron trichloride

Naming Molecular Compounds

You will not need to criss-cross oxidation numbers.

Molecular compounds name tells you the number of atoms through the use of prefixes.

Example

diphosphorus pentoxide

The name implies there are 2 phosphorous atoms and 5 oxygens.

P2O5

Example

sulfur hexaflouride

The name implies there is 1 sulfur atom and 6 fluorines.

SF6

Problem

Write the formulas for the following molecules. tetraiodide nonoxide

nitrogen trioxide

I4O9

NO3

Problem

Write the formulas for the following molecules. carbon tetrahydride

phosphorus trifluoride

CH4

PF3

Types of Compounds

Smallest piece

Melting Point

State

Types of elements

Formula Unit Molecule

Metal and nonmetal

Nonmetals

SolidSolid, liquid or gas

High >300ºC Low <300ºC

Ionic Molecular

Acids

Writing Names and Formulas

Acids Acids are compounds that give off

hydrogen ions (H+) when dissolved in water.

Acids will always contain one or more hydrogen ions next to an anion.

The anion determines the name of the acid.

Naming Binary Acids

Binary acids contain hydrogen and an anion whose name ends in –ide.

When naming the acid, put the prefix hydro- and change -ide to -ic acid.

Example HCl

The acid contains the hydrogen ion and chloride ion.

Begin with the prefix hydro-, name the nonmetallic ion and change -ide to -ic acid.

hydrochlorideic acid

Example

H2S The acid contains the hydrogen ion

and sulfide ion.

Begin with the prefix hydro- and name the nonmetallic ion.

hydrosulfide

Example

H2S

The next step is change -ide to -ic acid, but for sulfur the “ur” is added before -ic.

hydrosulfideic acidur

Problem

HF

H3P(hydrophosphoric acid)

(hydrofluoric acid)

Name the following binary acids.

Writing the Formulas for Binary Acids

The prefix hydro- lets you know the acid is binary.

Determine whether you need to criss-cross the oxidation numbers of hydrogen and the nonmetal.

Example

Hydrobromic acid The acid contains the hydrogen ion

and the bromide ion.

Example

Hydrobromic acid

H1+Br1-

The two oxidation numbers add together to get zero.

HBr

Example

Hydrotelluric acid The prefix hydro- lets you know the

acid is binary. The acid contains the hydrogen ion

and the telluride ion.

Example

Hydrotelluric acid

H1+Te2-

The two oxidation numbers do NOT add together to get zero, so you must criss-cross.

H2Te

Problem Write the formulas for the following

binary acids. Hydrocyanic acid HCN

Hydroselenic acid H2Se

Naming Ternary Acids The acid is a ternary acid if the anion

has oxygen in it. The anion ends in -ate or -ite. Change the suffix -ate to -ic acid Change the suffix -ite to -ous acid The hydro- prefix is NOT used!

Example

HNO3

The acid contains the hydrogen ion and nitrate ion.

Name the polyatomic ion and change -ate to -ic acid.

nitrateic acid

Example

HNO2

The acid contains the hydrogen ion and nitrite ion.

Name the polyatomic ion and change -ite to -ous acid.

nitriteous acid

Example

H3PO4

The acid contains the hydrogen ion and phosphate ion.

Name the polyatomic ion and change -ate to -ic acid.

phosphateoric acid

Problem

H2CO3

H2SO4

(carbonic acid)

(sulfuric acid)

Name the following ternary acids.

Problem

H2CrO4

HClO2

(chromic acid)

(chlorous acid)

Name the following ternary acids.

Writing the Formulas for Ternary Acids

The lack of the prefix hydro- from the name implies the acid is ternary, made of the hydrogen ion and a polyatomic ion.

Determine whether you need to criss-cross the oxidation numbers of hydrogen and the polyatomic ion.

Example

Acetic acid

H1+C2H3O21-

The polyatomic ion must end in –ate since the acid ends in -ic.

The acid is made of H+ and the acetate ion.

Example

The two charges when added equal zero.

H1+C2H3O21-

HC2H3O2

Example

Sulfurous acid

Again the lack of the prefix hydro- implies the acid is ternary, made of the hydrogen ion and a polyatomic ion.

Example

sulfurous acid

H1+SO32-

The polyatomic ion must end in –ite since the acid ends in -ous.

The acid is made of H+ and the sulfite ion.

Example

The two charges when added do not equal zero, so you must crisscross the oxidation numbers.

H1+SO32-

Example

Ignore the negative sign and ones are understood.

H1+SO32-

H2SO3

Problem

Write the formulas for the following ternary acids. perchloric acid

HClO4

iodic acid HIO3

naming compounds and writing formulas

Documents

type of charge

possible charge

overall charge

group number

strontium ion

lithium ion

negative ion

positive ion