NOTES Out 4 Writing formulas.doc

III. Outcome 4 Writing Formulas for Ionic & Covalent Compounds

A) How to:

Write Formulas for Ionic Compounds

1) Sodium (Na) is a _ (metal \ nonmetal) so it _ (takes in \ gives out) electrons to get to a full outer energy level. Sodium moves ___ (the number of) electrons so it is left with ___ (the number of) protons (+) and ___ (the number of) electrons (-). Therefore, sodium would have a charge of _____.

2) Sodium’s oxidation number =

Na

3) Oxygen (O) is a _ (metal \ nonmetal) so it _ (takes in \ gives out) electrons to get to a full outer energy level. Oxygen grabs ___ (the number) electrons so it is left ___ (the number of) protons (+) and ___ (the number of) electrons (-). Therefore, oxygen would have a charge of _____.

4) Oxygen’s oxidation number =

O

5) Draw electron dot diagrams for Na and O below:

Na

O

6) Chemical formulas are written to represent compounds (which are the atomic combination of two or more elements) with the __ [metal \ nonmetal] having the __ [+ / -] charge written first, and the __ [metal \ nonmetal] having the __ [+ / -} written second.

7) What is an ion?

HOW TO WRITING CHEMICAL FORMULAS

OXIDATION NUMBER - The number that represents the ionic charge of an atom.

a) Find the oxidation number of each ion. (If the oxidation number is +1or –1, the number is not written. Ex: Cl-₎

Example: Fe+2 _Cl

-b) Always write the + ion first.

c) Criss-cross the oxidation numbers and drop the charges. Example :

Fe

Cl

= Fe Cl

d) If the charges are the same or are divisible by 2 or 3 or any number, you reduce them.

In the chemical formula Fe Cl2 the numbers are not the same and are not divisible by any number so

we leave the numbers and write the formula: Fe Cl2.

If we were writing a formula for a compound of Mn+4 _{and O}-2_{, we would . . .}

Criss-cross the oxidation numbers:

Mn

O

Since the numbers are divisible by 2, in this case, we reduce them and get: MnO2

Write formulas for the following:

B)

Covalent Compounds

1) Covalent Bonds – Chemical bonds in which the atoms share the electrons. a) Formed between two nonmetals.

b) Atoms share one or more pair of valence electrons. c) Electrons are always in pairs.

1. bonding pair = shared pair ….. “Owned”by both atoms. 2. nonbonding pair …. “owned” by a single atom.

d) Always liquids or gasses at room temperature. 2) How to figure out Covalent Bonds:

a) COUNT …. Count the total valence electrons.

b) CONNECT …. Connect atoms using 2 electrons (bonding pair) … arranged around a central atom, if there is one.

c) FILL …. Work your way from the outside-in filling the octet (“duet rule” for Hydrogen) rule. d) CHECK … Are all valence electrons placed? Is octet filled for all atoms?

3) Some Covalent Lewis Dot Structure Practice Formula: Hydrogen: H2

Formula: Ammonia: NH3

Formula: Ethane: C2H6

Subscipts: Numbers used to represent

the number of

atoms of each

element in a compound

.

A. How To:

Write Formulas for Ionic

Write Formulas for Ionic

Compounds

Therefore, sodium would have a charge of +1.

3) Oxygen (O) is a _ (metal \

nonmetal

)

so it _ (

takes in

\ gives out) electrons to

get to a full outer energy level. Oxygen

grabs

2

(the number) electrons so it is

left

8

(the number of) protons (+) and

Therefore, oxygen would have

a charge of

-2

.

5) Draw electron dot diagrams

for Na and O below:

6)

Chemical formulas

--- represent

compounds

(

which are the atomic combination of two or

more elements

) with the __ [

metal

\ nonmetal]

having the __ [

+

/ -] charge written first,

and the __ [metal \

nonmetal

] having

7) What is an ion?

A electrically

HOW TO WRITE CHEMICAL FORMULAS

OXIDATION NUMBER

-

The number

that represents the ionic charge of an

HOW TO WRITE CHEMICAL FORMULAS

OXIDATION NUMBER - The number that represents the ionic charge of an atom.

a)

Find the oxidation number of

each ion

. (

If the oxidation number is +1or –1,

the number is not written. Ex: Cl

-

)

-a) Find the oxidation number of each ion. (If the oxidation number is +1or –1, the number is not written. Ex: Cl-₎

Example: Fe+2 _Cl

a) Find the oxidation number of each ion. (If the oxidation number is +1or –1, the number is not written. Ex: Cl-₎

Example: Fe+2 _Cl

-b) Always write the + ion first.

c) Criss-cross

the oxidation

numbers and drop the charges

.

Example :

Fe

+2

_Cl

c) Criss-cross the oxidation numbers and drop the charges. Example :

Fe

Cl

= Fe Cl

d) If the charges are the same or are divisible by 2 or 3

or any number, you reduce them.

In the chemical formula Fe Cl

2

the numbers are not the

If we were writing a formula for a

compound of Mn

+4

_{and O}

-2

_{, we}

would . . .

Criss-cross the oxidation

numbers

:

Criss-cross the oxidation numbers:

Mn

O

Drop the charges: Mn

2

O

4

Since the numbers are divisible by

2, in this case, we reduce them and

Write formulas for the following:

8) Na Cl

9) Mg S

10) Fe (2) O