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I

/

HOMOGENEOUS

YSTEMS

ND

THEIR

PROPERTIES

RULE.3-

The

third digit

from

the

right

is numerically

one less han

the

number

of

carbon

(c)

atoms

in

the

compound.

\{hen

this

digit

is zero,

it is

omitted from

the

number.

nule 4. The number of chlorine (cl) atoms n the compound s found by sub-

tracting

the

sum

of

the

fluorine

and

hydrogen

atoms

from

the

total

number

of atoms

that

can

be

connected

o

carbon. when

only

one

carbon

atom

is involved,

he

total

number

of

attached

atoms

s four.

when

two

carbon

atoms

are

present,

the

totar number

of

attached

atoms

s

six.

An application

of

the

first four

rules

in

determining

the

formula

for

fluoro-

carbon 12

s as ollows:

Deivation

of

the Formula

for

Ftuorocarbon

12

1.

The first

digit

on the

right

in

fluorocarbon

12is2.

Therefore,

he

com-

pound

contains

wo

fluorine

atoms

Rule

l).

2.

The

second

digit

fronr

the

right

is

1.

Therefore,

there are

no

hydrogen

atoms

n the

compound

Rule

2).

3.

The third

digit

from

the

right

is

zero

and

has

been

omitted from

the num-

ber.The compound hereforecontainsonecarbonatom (Rule 3).

4.

since

fluorocarbon

12

contains

one

carbon

atom, there are

four

other

atoms

attached

to

the

carbon

atom.

The

number

of chlorine

atoms is

found

by

subtracting

the

sum

of

the

fluorine

atoms and

the hydrogen

atoms

from

four.

There

are

two

fluorine

atoms

and no hydrogen

atoms.

Therefore,

there

are

two chlorine

atoms

n the

compound

(Rule

4).

summarizing

he

above

nformation,

fluorocarbon

12 containsone

carbon

atom,

two

fluorine

atoms,

and

two

chlorine

atoms.

Therefore.

ts

chemical

formula s CC12F2.

Additional

rules

are

necessary

o

desigrate

symmetry,

cyclic

character,

and

unsaturation.

nurp

5.

In

the case

where

isomers

exist,

each

has

the

samenumber,

but

the

most

symmetrical

s indicated

by the

number

alone. As the

isomers

become

more

and

more

unsymmetrical,

he

letters a,

b, c, etc.,

are

appended.

For

ethanes,

ymmetry

s

determined

by

dividing

he mole-

cule in two and addingt} e atomic weightsof the groupsattached o

each

carbon

atom.

The

closer

he

total

weights

are to each

other, the

more

symmetrical

he

product.

For propanes

nd higher

carbon

series,

symmetry

rules

become quite

complex.

since the

latter compounds

are

not

normally

used

in

the aerosol

industry,

symmetry rules

for

them

will

not

be

discussed

n

this

chapter.

An illustration of

symmerry

determination

or

isomers

of

fluorocarbon

114

s

as

ollows: