key question: why do atoms combine in certain ratios?

Key Question:

Why Do Atoms Combine In Certain Ratios?

Review of Oxidation Numbers

Review of Oxidation Numbers

All compounds have an electrical charge of zero (they are neutral).

An oxidation number indicates the charge on the atom (or ion) when electrons are lost, gained, or shared in chemical bonds.

Oxidation Numbers

A sodium atom always ionizes to become Na+ (a charge of +1) when it combines with other atoms to make a compound.

Therefore, we say that sodium has an oxidation number of 1+.

What is chlorine’s oxidation number?

Ionic Bonds

On the periodic table, strong electron donors are on the left side (alkali metals).

Strong electron acceptors are on the right side (halogens).

The further apart two elements are on the periodic table, the more likely they are to form an ionic compound.

Covalent Bonds

Covalent compounds form when elements have roughly equal tendencies to accept electrons.

Elements that are both nonmetals and therefore close together on the periodic table tend to form covalent compounds.

Oxidation Numbers, Lewis Structures And Chemical Formulas

Remember, the oxidation numbers for all the atoms in a compound must add up to zero.

Multiple Oxidation Numbers

Some periodic tables list multiple oxidation numbers for most elements.

This is because more complex bonding is possible.

Naming Compounds and Writing Formulas

5 Types Of Chemical Compounds

•Binary ionic - metal ion – nonmetal ion

•Ternary ionic - at least one ion is a polyatomic ion

•Binary molecular - two nonmetals

•Binary acid - H – nonmetal

•Ternary acid - H – Polyatomic ion

Tips To Keep In Mind When Naming And Writing Formulas:

•Always keep your Periodic Table handy – You should have it in front of you ALWAYS when you are naming and writing formulas.

•Remember that metalsmetals (except Hydrogen) are found to the left of the stairstep on the Periodic Table.

•NonmetalsNonmetals are found on the right side of the stairstep of the Periodic Table.

•Metalloids Metalloids are the 7 elements on or below the stairstep are the 7 elements on or below the stairstep except Al and At. For naming purposes they will tend to except Al and At. For naming purposes they will tend to behave like nonmetals.behave like nonmetals.

Naming Binary Compounds

A binary ionic compound is held together by ionic bonds.

Binary molecular compounds consist of covalently bonded atoms.

Each type of compound has its own naming rules.

How Do You Name Binary Ionic Compounds?

(Composed Of Two Elements – A Metal And A Nonmetal)

•Name the first ion

•From groups 1, 2, 3, 13, zinc, cadmium, or silver. (You must use a Roman Numeral with the name for the other metals – we’ll discuss this later.)

•Name the second ion changing the suffix to –ide.

Naming Binary Ionic Compounds

MgBr2 is magnesium (name of first element) + brom (root name of second element) + ide suffix = magnesium bromide

Examples

BaNa2You should recognize a problem with this one

This is two metals – not a binary ionic compoundThe name of this is BananaBanana (haha!!)

What is the name of this compound:

HIJKLMNO?

WATER – “H” to “O”

You have to admit – that was funny!

Exit QuizNaCl

Name the metal ionSodium

Name the nonmetal ion, changing the suffix to –ide.

Chloride

CaO

Calcium Oxide

Al2S3

Aluminum Sulfide

MgI2Magnesium Iodide

What About The Transition Metals And Using Roman Numerals? How Does That Work?

Let’s See.FeO

Notice – metal and nonmetal.Name the first ion. Since the first ion is a transition element, you must use a Roman Numeral to represent the charge.

How do you know the charge?

Deductive reasoning.

•All compounds are neutral.

•Oxygen has a -2 charge (group 16)

•Therefore, iron must have a +2 charge since there is one iron and one oxygen. Iron gets a Roman Numeral (II).

Iron (II) Oxide

Isn’t this easy and FUN!!!

Cu2SName the first ion. Since it is a transition metal, you must use a Roman Numeral.

Which Roman Numeral? The Roman Numeral is the same as the charge of the ion.

How do you find the charge?

Deductive reasoning!

•All compounds are neutral

•Sulfur has a -2 charge (group 16)

•There are two coppers.

•Therefore each copper must have a +1 charge for all ions to be neutral

Copper (I)Sulfide

MnO2Name the first ion. Since it is a transition metal, you must use a Roman Numeral.

How do you determine the Roman Numeral?

It is the same as the charge.

What is the charge of Mn?


•Oxygen (group 16) has a -2 charge.

•There are two oxygens and one Mn.

•Therefore Mn must have a +4 charge for this compound to be neutral.

Manganese (IV)oxide

So Why Must We Use Roman Numerals With Transition Elements?

•The metals in groups 1, 2, 3, and 13 have single, definite charges.single, definite charges.

•Group 1 metals have a +1+1 charge.

•Group 2 metals have a +2+2 charge.

•Groups 3 and 13 metals have a +3+3 charge.

•Transition metals may have multiple charges – usually two different positive charges.

For example, there are two copper oxide compounds:

Cu2O and CuO We can’t just say Copper oxide. Which one of these is Copper oxide? We must distinguish these

by using a Roman Numeral

Cu2O

Copper I oxide

Copper is +1

CuO

Copper II oxide

Copper is +2

There Are Three Transition Elements Which Do Not Require A Roman Numeral Because They Have Single

Definite Charges. These Are

Zinc – Zn2+ Cadmium – Cd2+ Silver – Ag+

You need to remember the charges for these.

Ag2O Name the first ion.

Silver Name the second ion changing the suffix to –ide.

oxide

ZnCl2Name the first ion.

Name the second ion changing the suffix to –ide.

Zinc chloride

No Roman Numerals needed for these.

How Do You Write Formulas For Binary Ionic Compounds Given The Name?

Two Simple Steps:

1. Write the symbol and charge of each ion

2. Balance the charges by providing subscripts

Magnesium chloride Write the symbol and charge of each ion.

Mg2+ Cl-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

Cl-

MgCl2

Iron (III) bromide

Write the symbol and charge of each ion. The charge of the iron is provided by the Roman Numeral.

Fe3+ Br -

Balance the charges by supplying subscripts. The subscripts tell how many of each ion is needed to balance the compound.

You’ll need three bromine ions to balance the one iron.

Br -

Br -

FeBr3

Aluminum Sulfide Write the symbol and charge of each ion.

Al3+ S2- 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

Al3+ S2-

S2-

Al2S3

Writing Formulas a Little Quicker

Iron and oxygen combine to form a compound. Iron (Fe) has an oxidation number of 3+. Oxygen (O) has an oxidation number of 2–.

Predict the chemical formula of this compound.

1. Given … Fe3+ and O2–

Write the subscripts so that the sum of the oxidation numbers equals zero.

2. Solution Two iron atoms = 2 × (3+) = 6+ Three oxygen atoms = 3 × (2–) = 6–


Fe

3+ O

2-

3 2x = 6


Fe 3+

+

= +6

Fe 3+

O2-

+O

2-

+O

2-

= -6+6

-6

0


Fe

3+ O

2-

32


Exit Quiz – Formula for magnesium chloride?Exit Quiz – Formula for magnesium chloride?

MgCl2

2+ 1-

Exit Quiz – Formula for sodium oxide?Exit Quiz – Formula for sodium oxide?

Na2O

1+ 2-

Exit Quiz – Name for:

Fe2O3

3+ 2-Iron (III) oxide

Exit Quiz – Formula for:

CrO2

4+ 2-Chromium (IV) oxide

Exit Quiz – Charge on Chromium?

Cr2O72-

6+ 2-

Second Category Of Compounds – Ternary Ionic Compounds.

These Compounds Contain At Least One Polyatomic Ion.

What is a polyatomic ion?

Let’s look at the name to try to understand.

•It is an ionion – that means it has a charge.

•It is polyatomicpolyatomic – that means it is made of more than one atom.

Let’s look at some examples of polyatomic ions.

CO32- carbonate

This ion is composed of one carbon and three oxygens and the entire group

has a charge of -2.

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

You have been given a list of other polyatomic ions

You need to learn these!!!

How Do You Recognize Ternary Ionic Compounds?

Composed of two ions in which at least one is a polyatomic ion.

There is only one positive polyatomic ion (NH4+)

Three possible types of Ternary Ionic Compounds:

•Ammonium + negative ion (nonmetal)

•Metal (positive ion) + negative polyatomic ion

•Ammonium + negative polyatomic ion

Polyatomic Ion

Naming Compounds with Polyatomic ions

NH4Cl is ammonium (the name of the ion from chart) + chlor (root name of the second element) + ide suffix = ammonium chloride.

How Do You Name Ternary Ionic Compounds?

1. Name the first ion.

2. Name the second ion. Isn’t that simple??!!

Examples:Na2CO3

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.

Name the first ion.

Sodium

Name the second ion.

carbonate

Notice that you do NOT change the suffix – just name the polyatomic

ion

Fe(OH)3 Name the first ion.

Iron Remember that iron requires a Roman Numeral since it is a transition element. What Roman Numeral should be used?

The Roman Numeral comes from the charge of the ion. How do you find the charge of the iron?

You know two things:


•You know the charge of OH (-1)

Since there are 3 OH groups, each with a -1 charge, the charge of the iron must be +3 for the compound to be neutral

(III)

Name the polyatomic ion.

hydroxide

NH4Cl Name the first ion.

Ammonium Name the second ion.chloride

Notice that since the second ion is a nonmetal that, like binary ionic compounds, the suffix of the nonmetal changes to –ide.

(NH4)3PO4

Name the first ion.

Name the second ion.Ammonium phosphate

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

Cu2SO4Name the first ion.

CopperYou should realize that you need a Roman Numeral since copper is a transition metal.

The Roman Numeral is the same as the charge.

What is the charge?

The charge of sulfate is -2.

Since there are two coppers, the charge of the copper must be +1.

(I) sulfate

Name the second ion.

How Do You Write Formulas For Ternary Ionic Compounds?

Very Much Like Writing Formulas For Binary Ionic Compounds.

Three Steps:

1. Write the formulas/symbols of each ion.

2. Balance the charges by supplying subscripts.

3. 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.

Al3+ NO3-

Balance the charges by supplying subscripts.

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

balance one Al3+

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

this in parentheses with the 3 outside.

Al(NO3)3

Lead (IV) acetate Write the formula/symbol and charge of each ion.

Pb4+ C2H3O2-

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

-1 to balance 1Pb+4

Pb(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

Ca2+ PO43-

Ca3(PO4)2

Exit Quiz

Al3+ combines with sulfate (SO4)2– to make aluminum sulfate.

Write the chemical formula for aluminum sulfate.

Al3+(SO4)

2-

32

Exit Quiz Answer

The Third Category of Compounds –

Binary Molecular

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 – You Must Use Prefixes.

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

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

Steps

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

Naming Binary Molecular Compounds

As with binary ionic compounds, the ending of the name of the second element in the compound is modified by adding the suffix –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.

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 name it aluminum chloride.

Given The Names Of Binary Molecular Compounds, How Do You Write The Formulas?

Very easily done!!! 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.

Is this not sooooooo easy!??

CO2

Carbon dioxide

SO

Sulfur monoxide

N2O5

Dinitrogen pentaoxide

CF4

Carbon tetrafluoride

SO3

Sulfur trioxide

CO

Carbon monoxide

B2O3

Diboron trioxide

NF5

Nitrogen pentafluoride

Exit Quiz

More Practice with Covalent CompoundsMore Practice with Covalent Compounds

Covalent compounds are made of two nonmetals, which from the

periodic table are always expected to be negative


But since covalent compounds are neutral species, it is not possible

for every element to retain its negative oxidation number


ONLY THE MORE ELECTRONEGATIVE ELEMENT keeps

its negative oxidation number. Other nonmetals must adapt to keep the

compound neutral

Electronegativity TrendElectronegativity Trend


SO2

Since oxygen is the more electronegative element, it will

have its normal oxidation number.

-2


SO2

The compound is neutral, so the oxidation number of sulfur will be sufficient to balance out the two

oxygen atoms. What is it?

-2+4


OF2

Since fluorine is the more electronegative element, it will


-1


OF2

The compound is neutral, so the oxidation number of oxygen will be sufficient to balance out the two fluorine atoms. What is it?

+2 -1


PO43-

Since oxygen is the more electronegative element, it will


-2


PO43-

-2

The ion has a charge of negative three, so the oxidation numbers must add up to the total charge

of the ion. What is it?

+5

More Practice: Ionic Compounds with More Practice: Ionic Compounds with PolyatomicsPolyatomics

CaSO4

This is an ionic compound, so the charge of the metal cation is its oxidation number. What is it?

+2


CaSO4

The anion is a polyatomic ion, sulfate, and the charge of sulfate

is what? So the oxidation numbers of

sulfur and oxygen must add to -2.

+2


CaSO4

Oxygen is the more electronegative of the two, so it

keeps its normal oxidation number. What is it?

+2 -2


CaSO4

Sulfur and the four oxygen atoms must add to negative two (the charge of the sulfate anion).

What is the charge on sulfur?What is the name?

Calcium sulfate.

+2 -2+6


Pb(OH)4This is an ionic compound, so the charge of the metal cation is its oxidation number. But this is a transition metal, so we cannot know it from its position on the

periodic table.


Pb(OH)4But the anion, the hydroxide ion,

carries a charge of negative one. All four hydroxides are negative one, but

since the compound is neutral, the oxidation number of lead must

balance it out. What is it?

+4


Pb(OH)4Within the anion, oxygen is the more electronegative of the two elements, and keeps its normal oxidation number. What is it?

+4 -2


Pb(OH)4Within the hydroxide ion, the oxygen and

hydrogen must add to the charge of the ion, -1. What is the charge on H?

What is the name?Lead (IV) hydroxide

+4 -2 +1

key question: why do atoms combine in certain ratios?

Documents

naming binary compounds

naming compounds

magnesium bromide slide

binary ionic compound

binary molecular compounds

ionic bonds

multiple oxidation numbers

review of oxidation