FORMULA WRITING, GFW,

% MASS, AND HYDRATES

Say what??

One metal + one non-metal

Formula Writing

Ionic Compounds

Let’s Review

Fill in the charges

More Review

How are ions formed?

Positive ions –

Aka:

Negative ions –

Aka:

Lets Write Some Formulas…

_______________ ions are ALWAYS written first.

If more than one ion can exist, use parentheses and the charge in roman numeral form

Ie: Cu+2 is named copper (II)

_______________ ions are ALWAYS written second.

So…

Can two positive ions ever be put together?

Can two negative ions ever be put together?

How do you know what numbers to use?

Criss-Cross Method

Identify the charge of each ion

“criss-cross” the charges ignore the + and –

Numbers become subscripts

Let’s do a few examples… pick any cation and

anion:

Naming Compounds

Cation stays the same

Anion ending changes to –ide

Often this simply involves changing the –ine ending

Chlorine chloride

Fluorine fluoride

Bromine bromide

However, there are some you need to remember:

Examples:

Phosphorus phosphide

Sulfur sulfide

Oxygen oxide

Let’s do some more practice…

Charges Criss Cross Name

Ca and Cl

Ba and O

Cu and I

Formula Writing

Polyatomic Ion Compounds

Polyatomic Ions

Remember:

___________________ is written first

___________________ is written second

New:

Put parentheses around the

______________________________ ion

Naming the Compounds with

Polyatomics

You need to remember the Polyatomic Ions

If single element: cation and anion is the same

If polyatomic: use names provided

Some Polyatomic Practice

Write the formula the following:

Formula Name

Ba +2 C2H3O2 -1 ________________ _____________________

Al +3 PO4 -3 ________________ _____________________

K +1 SO4 -2 ________________ _____________________

Ca +2 NO3 -1 ________________ _____________________

2 non-metals together

Formula Writing

Covalent Molecules

Writing Formulas

Remember, bonds require 2 electrons

Covalent is the sharing of electrons

Naming Covalent Compounds

The less electronegative element is written first.

Remember the trend (increasing up and to the right)

Use a number indicating prefix only if more than one

atom is present

Ie N2 is dinitrogen

A prefix is always added to the name of the second

element

Will change ending of name to –ide (just like ionic

bonds)

Naming Covalent Compounds - Rules

Leave the "a" off the end of the prefixes that end in "a" and the “o” off of mono-if they are placed in front of an element that begins with a vowel.

Number Indicating Prefixes:

mon(o) -1

di -2

tri -3

tetr(a) - 4

pent(a) -5

hex(a) - 6

hept(a) - 7

oct(a)- 8

non(a) -9

dec(a) -10

Try Some Practice

N2S4

NI3

CCl4

P2O5

Dinitrogen tetrasulfide

Nitrogen triiodide

Carbon tetrachloride

Diphosphorus pentoxide

Common Names

H2O - water

NH3 - ammonia

CH4 - methane

C2H6 - ethane

C3H8 - propane

Formula Weight

Molecular Mass

The molecular mass is the same numeric value

as the atomic mass but the unit is different

Atomic mass is measured in atomic mass units (amu)

Molecular mass is measured in grams

So molecular mass is the atomic mass with the

unit “grams” or “g”

Molecular Mass

Formula Weight

Formula weight of a compound is the sum of

the atomic masses of the atoms

As given in the formula of the compound.

Sum of molecular masses

Formula Weight

Steps:

1. Determine how many moles of each element are

in the compound using the subscripts.

2. Find the molecular mass of each element in the

compound by multiplying #1 and atomic mass.

3. Add it all together

We will use a table that looks like this…

Element # Atoms Atomic Mass Molecular Mass

Formula Weight~ Example

1. Determine atoms

first…

Subscripts in formula

No parentheses moles = subscripts

Parenthesizes moles = outer subscript x inner subscript

Element # Atoms Atomic Mass Molecular Mass

Aluminum 1

Bromine 3

Formula Weight ~ Example

2. To find the molecular mass of aluminum and bromine:

3. Add elements molar masses together to get compounds molar

mass:

= 266.68 g/mol AlBr3

Element # Atoms Atomic Mass Molecular Mass

Aluminum 1 26.98 g

26.98 g

Bromine 3 79.9 g 239.70 g

Percent Composition

Percent Composition

The percent that you find of any ONE element in a

compound of elements.

Found by taking the PART that you are looking for

and dividing it by the WHOLE.

Then multiply by 100 to move decimal.

Percent Composition

What percent of 92 is 42?

In other words, the part “42” of the whole “92” is what percent?

42/92 x 100 = 45.7%

Percent Composition and Chemistry

Now, take the PART (Ca) and divide it by the WHOLE.

Multiple by 100.

= 310.19g/mol

Element # Atoms Molecular Mass % Composition

Ca 3 120.24 g 120.24/310.18

x100 = 38.8%

P 2 61.95 g

O 8 128.00 g

Hydrates

What are hydrates?

Hydrates- compounds that contain H2O in their

structure

Different from water because the H2O is part of

the molecule (not just surrounding it).

H2O can usually be removed if heated.

Writing Hydrates

A dot separates water

e.g. CuSO4 • 5H2O is copper(II) sulfate pentahydrate.

Naming- use prefix to show how many H2O are

present

mono - 1

di - 2

tri- 3

tetra - 4

penta- 5

hexa – 6

hepta – 7

octa - 8

nona - 9

deca- 10

Examples…

sodium sulfate decahydrate

nickel(II) sulfate hexahydrate

Na2CO3•H2O

BaCl2•2H2O

Na2SO4•10H2O

NiSO4•6H2O

sodium carbonate monohydrate

barium chloride dihydrate

Hydrate Uses

Chloral Hydrateprescription drug that is used for the short-term treatment of insomnia.

Terpin hydrate helps to loosen mucus

Ice That Burns: Gas Hydrates Offer a Potential Energy Reserve, Danger to Petroleum Exploration & Global Warming Concern

As the methane diffuses through the sediment, it combines with water at the low temperatures and high pressures beneath the ocean to produce an ice-like solid.

More Hydrate Uses

A colorful example is cobalt(II) chloride, which

turns from blue to magenta (red) upon hydration,

and can therefore be used as a water indicator.