Chapter 7, Sections 1-2 · Chapter 7, Sections 1-2 Chemical Formulas & Compounds Nomenclature and...

Chapter 7, Sections 1-2 Chemical Formulas & Compounds Nomenclature and Oxidation numbers

C. Goodman, Doral Preparatory Academy, 2011-2014

Based on a PowerPoint by Mrs. S. Temple,

Essential Questions – Section 1

1. Binary ionic compounds

How can you determine their names and

chemical formulas?

2. Binary molecular compounds

How can you determine their names and

chemical formulas?

Vocabulary – Section 1

1. Acid

2. Binary ionic

compounds

3. Formula unit

4. Chemical

formula

5. Monatomic ion

6. Polyatomic ion

7. Subscript

Chemical Formula

Relative # of atoms of each kind

in…

a. Molecules: a single molecule

b. Ionic compound: formula unit

Examples

How many atoms are in each

compound? CH4 (methane)

Pb(NO3)4 (lead (IV) nitrate)

1. Cations

Element’s name

Al3+ is…

Aluminum

2. Anions

Drop ending of elements name, add “–ide”

Cl- is…

chloride

Nomenclature:

Ionic compounds I: Ions

Cation’s charge =

+(number of valence electrons lost during ion formation)

Formation of Cations

Also:

Cadmium Cd2+

Gallium Ga2+

Zinc Zn2+

Silver Ag+

Anion’s charge =

-(#electrons gained during ion formation)

Formation of Anions

Practice naming anions! Element symbol

& name

Name of anion Charge

N – nitrogen Nitride 3-

S – sulfur

Se – Selenium

O – oxygen

P – phosphorus

Cl – chlorine

F – fluorine

H – hydrogen

Br – bromine

I – iodine

Naming Ionic Compounds II: Binary Ionic compounds 2 elements

+ and – charges

must balance (= 0)

Smallest possible

whole number ratio

Nomenclature:

Type I Binary Ionic Compounds

1. Write the name of

the cation

2. Append the name of

the anion

Example:

Al2O3

Aluminum

Aluminum oxide

The cations of Type I

compounds are those

with “reliable” charges.

Predicting the formula of an

ionic compound using the

“Criss-cross” method

1. Put the ions next to each other, cation first

2. Criss-cross – charges to subscripts

3. You’re done!

Notes:

a. If need be, reduce the subscripts to the lowest whole number ratio.

b. Do not write “1” as a subscript – it is understood

Example:

Aluminum and oxygen

Al3+ O2-

Al2O3

Practice! Cation Anion Formula Name

Na+ O2- Na2O Sodium oxide

Al S

Mg Cl

Lithium chloride

Sr O

Hydrogen sulfide

K F

Aluminum bromide

More Practice!

Cation Anion Formula Name

Strontium

nitride

Rb P

Barium sulfide

Cd P

Hydrogen

phosphide

Zn N

Problem!

This is easy when you’re working with

the “reliable” cations, which we

learned above.

BUT…

Most metals can have varying charges

What happens when you have a

compound with one of these metals?

Introducing… the STOCK SYSTEM!!!

(pause for applause)

Nomenclature:

Stock System

(Type II compounds)

Roman numeral after cation’s name indicates

charge of cation

Example: Copper (III) chloride … Cu3+

Example: Iron (II) oxide … Fe2+

The cations of Type II

compounds are those

with “variable” charges.

Nomenclature of ionic compounds

using the Stock system

1. Write name of cation &

parentheses

2. Cation’s charge in parentheses

(Roman Numerals)

3. Name of anion

Example: Cu3+ & Oxygen

Copper ( )

Copper (III)

Copper (III) oxide

Practice!

Cation Anion Formula Name

Example

Cu+

O2-

Cu2O

Copper (I) oxide

Fe3+ S2- Iron (III) sulfide

Cu2+ Cl-

Tin (II) fluoride

Hg2+ O2-

Sn4+ S2-

Vanadium(III) iodide

V3+ Br-

Problem: when I look at the formula unit, how do I determine the cation’s charge? Example: Cu2O

“Reverse Criss-cross”!!!

Stock system continued…

Getting the name from a formula unit

Reverse criss-cross

Example: Cu2O3

1. Give the anion its normal

charge.

2. Reverse criss-cross to get the

charge of the cation. Keep the

subscripts as well.

3. BUT… you’re not done until

you…

4. Check charges to make sure

that they balance: multiply

subscript x superscript

Cu3+ = Copper (III)

Copper (I) oxide

Cu23+O3

2-

3+ 2-

x 2 x 3

6+ 6-

You’re cool!

Cu23+O3

2-

What if the charges don’t

balance? Example: SnS2

1. Adjust the cation’s

charge

2. Stock system

nomenclature

3. You’re done!

Sn2+S2

2-

2+ 2-

x 1 x 2

2+ 4-

Sn4+S2

2-

Tin (IV) sulfide

Practice Time!

Name Cation

charge

Anion

charge

Formula unit

Example

Copper (III) phosphide

Cu3+

P2-

Cu2P3

Iron(III) sulfide

Tin (IV) phosphide

Mercury(I) bromide

FeCl3

HgFl2

CuO2

More Practice!

Formula Criss-

cross

Cation’s

charge

Name

Example

VS2

Sn4+

Tin(IV) sulfide

CoI2

HgI2

PbS2

Copper (II) bromide

Iron (II) sulfide

Copper (II) oxide

Cobalt (III) fluoride

VS2 2-

Stock system continued… Determining the formula unit starting from the name

Example: Copper (II) chloride 1. Write the ions, cation first

2. Criss-cross

3. Check charges to make sure

they balance

4. Write formula unit

Cu2+Cl-

Cu12+Cl2

-

Cu12+Cl2

-

2+ 1-

x 1 x 2

2+ 2-

CuCl2

Polyatomic Ions A charged group of COVALENTLY

bonded atoms

Understanding Formulas for

Polyatomic Ionic Compounds

Polyatomic ions: Oxyions

Polyatomic ions that contain oxygen,

Example: hydroxide OH-

Usually more than 1 type of each

Example: BrO3

-(bromate), and BrO- hypobromite

You must memorize all of the Polyatomic Ions on Page 226 in your Chemistry Book!

PLEASE NOTE

Naming

Oxyanions

If it contains…

O or O2 = (hypo) …

ite

O3 or O4 =(per) …ate

or O4 = per … ate

The prefixes and

suffixes depend on the

number of oxygens in

the ion.

e.g. ClO- hypochlorite

NO2- nitrite

e.g. NO3- nitrate

ClO4- perchlorate

Determining formula units for

compounds containing oxyanions,

using the “Criss-cross” method

1. Put the ions next to each

other

2. Criss-cross –

3. Check charges

4. If need be, reduce the

subscripts to the lowest

whole number ratio.

Example:

Lead (IV) sulfate

Pb4+ (SO4)2-

Pb4+ (SO4)2-

2 4 4+ 2-

x 2 x 4

8+ 8-

Pb2(SO4)4

Pb(SO4)2

Practice!

SnS2 2-

Name Cations Anion Formula unit

Example

Titanium (IV) cyanide

Ti4+

(CN)-

Ti(CN)4

Iron(III) sulfide

Tin(IV) phosphate

Mercury(II) cyanide

Fe2(CrO4)3

Sn(ClO4)4

Hg(NO2)2

Co(OH)3

Common Binary Acids See textbook p. 230

Most common acids hydrogen + halogen

Oxyacids: hydrogen + oxyanion

Memorize:

◦ Hydrochloric acid HCl

◦ Hydrofluoric acid HF

Memorize

◦ Phosphoric acid H3PO4

◦ Nitrous acid HNO2

◦ Nitric acid HNO3

◦ Sulfurous acid H2SO3

◦ Sulfuric acid H2SO4

◦ Acetic acid CH3COOH

◦ Perchloric acid HCl)4,

◦ Carbonic acid H2CO3

Naming Binary Molecular Compounds

Prefixes

a) Use with

binary

molecular

compounds

b) memorize

these prefixes

1-10

Let’s try a few!

Molecular Formula Name

Example:

Mo2O3

Molybdenum trioxide

CCl4

PCl5

Selenium hexafluoride

Diarsenic pentaoxide

Essential Questions – Section

7.2 1. What are oxidation numbers?

2. How are oxidation numbers assigned?

Vocabulary – Section 2

1. Oxidation number

2. Oxidized

3. Reduced

Hold the phone!

Why do I have to

learn oxidation

numbers?

•Oxidation numbers are helpful in

chemistry. They are helpful in…

•naming binary molecular compounds

•writing balanced equations and writing

formulas.

•predicting what compounds can be made

out of two or more elements.

Hold the phone #2

How are oxidation

numbers different

from ionic charges?

Thank you for asking that question!

Oxidation numbers are related to

electronegativity, how tightly elements

hold their electrons. Unlike charges,

oxidation numbers apply to

nonmetals. Nonmetals can have

multiple oxidation numbers.

Two vocabulary words

Oxidized – an atom is oxidized when

other elements have pulled the

electrons away from it

Reduced – an atom is reduced when it

pulls the electrons closer to it

Why oxidation numbers?

Oxidation numbers are assigned in

order to indicate the distribution of

electrons among bonded atoms in

compounds or polyatomic ions.

Assigning Oxidation Numbers

Q: Why do I need to assign them?

A: Many elements can have more

than one oxidation state Note: the graphic below does not show all

possible oxidation numbers for elements in

groups 13-17.


Just follow

some simple

guidelines.

… and it’s

purrrr-tty

easy to do.


Step #1 Make an algebraic

statement

Step #2 Assign known oxidation

numbers first

Step #3 Solve for the unknown

oxidation number(s)

Assigning oxidation numbers

The sum of all oxidation numbers

in a compound equals …

0 for anything with a neutral charge

e.g. elements and molecules

OR

Ionic charge for ions

Step 1

Algebraic

Statement

Practice Problem #1:

Assign oxidation #s

for the elements in

the compound NaCl.

Step by Step Application

1. Make an algebraic sum

2. Assign known oxidation

numbers

3. Solve for the unknown

oxidation number

4. Put oxidation numbers in

“order of appearance”

1. Sum

{Na} + {Cl} = 0

2. Known Na’s oxidation number is +1

3. Solve

+1 + {Cl} = 0

{Cl} = -1

4. Answer

+1, -1


Assign known oxidation numbers first,

and then solve for what’s left.

Assign “knowns” in order of

precedence.

As in school, there is a pecking order…

Step 2, continued

Assign “Knowns”,

solve for the “unknown”


I. The senior class These elements always have the same oxidation

numbers, so assign them first:

a. Group 1 = +1

(with the exception of H)

b. Group 2 = +2

c. Fluorine = -1

Step 2, continued




I. The senior class Examples:

Determine the oxidation numbers for the elements in

the following compounds:

a. KI

b. Li2S

c. SF4

d. Na4O

Step 2, continued




I. The junior class

These elements almost always have the same

oxidation numbers, unless this would contradict the

“senior class” rules, so assign them second:

a. H = +1

UNLESS it is paired with an element

whose electronegativity is <2.1

b. Oxygen = -2

UNLESS it is paired with a “senior”

Step 2, continued




I. The junior class Examples:

a. CO2

b. ClO3-

c. H2SO4

d. NiH

e. OF2

Step 3

Solve for the “unknown”


I. The sophomore class If “senior” and “junior” rules don’t apply, assign oxidation

numbers according to electronegativity

1. The element with the highest electronegativity gets an

oxidation number equivalent to its charge.

2. If the electronegativities of the two elements are the same,

assign oxidation numbers to those who have definite ionic

charges first.

Step 2, continued

Assign “Knowns”


I. The sophomore class Examples:

a. CS2

b. ICl3

c. AlBr3

d. GeS2

Step 3

Solve for the “unknown”


I. What about the freshman class??? The freshman class consists of all of the other elements.

They have to fit in with all of the other rules.

Step 2, continued




SEE HANDOUT!!

Let’s try some together……

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Chapter 7, Sections 1-2 · Chapter 7, Sections 1-2 Chemical Formulas & Compounds Nomenclature and...

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