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Chapter 9 Notes, part I. Writing Ionic Formulas. Compounds. Up until now, we have only looked at single elements. There are only (to date) just over 100 elements, so how do we account for there being so many different types of stuff?. Compounds.

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Chapter 9 Notes, part I

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Chapter 9 Notes, part I

Writing Ionic Formulas


Compounds

  • Up until now, we have only looked at single elements.

  • There are only (to date) just over 100 elements, so how do we account for there being so many different types of stuff?


Compounds

  • There are millions of different compounds—two or more elements that are combined chemically.

  • The two types of compounds we will discuss in this chapter are ionic compounds and covalent compounds.


Ionic Compounds

  • Last chapter we discussed ions—elements that have a charge due to losing or gaining electrons.

  • Ionic compounds are made of ions.


Ionic Compounds

  • Metals tend to form ions by losing electrons, giving them an overall positive charge. These are called cations.

  • Nonmetals tend to form ions by gaining electrons, giving them an overall negative charge. These are called anions.


Ionic Compounds

  • An ionic compound is formed from a cation and an anion, which means they are usually formed from a metal and a nonmetal.


Ionic Compounds

  • Anions and cations can also be made up of a group of elements bonded together that carry an overall charge.

  • These groups of elements are called polyatomic ions.


Ionic Compounds

  • Even though an ionic compound is made from charged particles, it is still electrically neutral.

  • This means that its total charge is always EQUAL TO ZERO!!!


Chemical Formulas

  • SIDENOTE: The smallest part of an ionic compound is called a formula unit—just like the smallest part of an element is called an atom.

  • A chemical formula is like the recipe of a compound—it tells you the type and number of each element in the compound.


Writing Chemical Formulas

1) Write the symbol for the elements and their oxidation number, positive ion first (the metal).

EX: For a compound of Magnesium and Chlorine

Mg

+2

-1

Cl


Writing Chemical Formulas

2) Criss cross the numbers and write them as subscripts without the signs.

Mg

+2

2

-1

1

Cl


Writing Chemical Formulas

3) If there is a one charge, do not write it.

Mg1Cl2

MgCl2


Writing Chemical Formulas

4) If you have subscripts that are multiples, reduce them down.

+4

4

-2

2

Pb

O

1

2


Writing Chemical Formulas

5) If using polyatomic ions, put parentheses if there are more than one.

+2

2

-1

1

(

)

Ca

NO3


Writing Chemical Formulas

Here’s an example of a polyatomic that doesn’t have parentheses.

+1

1

-3

3

Na

PO4


Practice These:

BaCl2

Barium and chlorine

Rubidium and nitrogen

Lithium and phosphate

Iron (III) and nitrate

Manganese (IV) and sulfur

Rb3N

Li3PO4

Fe(NO3)3

MnS2


Naming Ionic Compounds


Naming Ionic Compounds

For ionic compounds where the metal always has the same oxidation number,

1) Name the metal.

EX: BaBr2

Barium


Naming Ionic Compounds

For ionic compounds where the metal always has the same oxidation number,

2) Write the name of the non-metal, and change the end to –ide.

EX: BaBr2

Barium

brom

ine

ide


Naming Ionic Compounds

If there is a polyatomic anion, then you do not change the ending:

EX: Ca(NO3)2

Calcium

nitrate


Name These:

Na2O

MgCl2

Na2CO3


Naming Ionic Compounds

  • If a positive ion (a metal) can have more than one oxidation number, you have to designate its charge in the name!

    We do this by putting the charge as a roman numeral in parenthesis between the positive and negative ion.


Naming Ionic Compounds

Why do we need to do that?

Name: Fe2O3

FeO

These both exist in nature, so we have to show which one we mean.


Naming Ionic Compounds

+3

Reverse criss cross to find the charge of the iron:

If this is true, then what was iron to begin with?

Fe2O3

Name it:

-2

Iron

(

)

ox

ygen

ide

III


Naming Ionic Compounds

+2

-2

Reverse criss cross to find the charge of the iron:

If this is not true, the numbers must have been reduced.

FeO

Name it:

-1

Iron

(

)

ox

ygen

ide

II


Naming Ionic Compounds

Metals that don’t need parentheses:

Group I, II and IIIA

Zn, Cd (always +2) and Ag (always +1)

Which means transition, inner transition and other metals do!


Naming Ionic Compounds

Final flowchart of how to name:

Name the positive ion.

Does it need a roman numeral?

If so, reverse criss cross, if not, ignore.

Name the negative ion and:

If a nonmetal end in -ide; if not, end normally


Name these:

Na2S

CuCl2

K2SO4

Pb(NO3)4


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