Chemical Names and
Formulas
Molar Mass


Molar mass relates moles to grams
The molar mass is the mass in grams of 1 mole of
an element or compound

Use the mass numbers from the periodic table, instead of
amu’s, the units are grams
Molar masses are computed in
the typical way
Percentage Composition

Percentage composition is the
percentage by mass of each element
in a compound

The chemical formula gives the ratio of atoms in a
compound

The chemical formula can also give the ratio of ions
to one another
Significance of a Chemical
Formula


For molecules, the formula gives the
number of atoms of each element
present in the molecule
For ionic compounds, the formula
gives the simplest ratio of cations (+)
and anions (-) in the crystalline lattice

Called a formula unit

The subscript refers to what is immediately
in front of it
Monatomic Ions




By gaining or losing electrons, single
atoms will become ions
Cations (+) will keep their atomic name
Anions (-) will change their ending to
-ide
Rather than gain or lose, some atoms
will share their electrons

This is called a covalent bond
Binary Ionic Compounds



Made of two different elements
The total number of positive and
negative charges must be equal
The cation will be written first, the
anion second
Al2O3
Aluminum Oxide
Aluminum +3
Oxide -2
Stock System of
Nomentclature


Some elements
form two or more
cations
System uses
Roman numerals to
indicate an ion’s
charge
Polyatomic Ions


Atoms that are covalently bonded to
one another, but as a group have
gained or lost electrons (forming a
charge)
Many are oxyanions (contain oxygen)




The most common one ends in –ate
The one with less oxygen ends in –ite
If there is one with less oxygen than –ite,
it is also given the prefix hypoIf there is more oxygen than –ate, it is
given the prefix per-
Naming Binary Molecular
Compounds

There are two naming systems


Stock system
Prefixes
Covalent-Network Compounds

Some covalent compounds do not
consist of individual molecules



Each atom is joined to all of its neighbors
in a covalently bonded, 3-dimensional
network
The subscripts in these formulas indicate
the smallest whole-number ratio of the
atoms in a compound
The naming scheme is the same as other
molecular compounds (SiC, SiO2, Si3N4)
Silicon Carbide, Silicon Dioxide, Trisilicon tetranitride)
Acids and Salts

Most acids are either Binary or Oxyacids

Binary acids consist of two elements


Usually hydrogen and one of the halogens
Oxyacids contain H, O, and a third element

Usually a non-metal

An ionic compound composed of a
cation and the anion from an acid is
often referred to as a salt.
Oxidation Numbers

In order to indicate the general
distribution of electrons among the
bonded atoms in a molecular
compound or a polyatomic ion,
oxidation numbers, also called
oxidation states, are assigned to the
atoms composing the compound or
ion.
p. 216
Saturated Hydrocarbons


Saturated Hydrocarbons are
hydrocarbons in which each carbon
atom in the molecule forms four single
covalent bonds with other atoms
Hydrocarbons that contain only single
bonds are alkanes


A
homologous
series is one
in which
adjacent
members
differ by a
constant unit
For alkanes,
the series
formula is
CnH2n+2

The systematic naming
system for compounds
was developed by
IUPAC


The basic part is the
name of the longest
carbon chain
The number of carbon
atoms is reflected in the
prefix, while the suffix –
ane indicates the
molecule has all single
bonds


The naming of branched-chain alkanes also
follows a systematic method
The branches are called alkyl groups


They are formed when a hydrogen is removed
from an alkane molecule
Named by changing the suffix from –ane to –yl.

To name this molecule, locate the longest
continuous carbon chain that contains the
most straight chain branches

Do not be tricked by the way it is drawn, the
longest chain may be bent



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Name the parent
hydrocarbon and add the
suffix –ane
Next identify the alkyl groups
Arrange the names in
alphabetical order in front of
the name of the parent
hydrocarbon
If there are multiple groups,
use the prefix di, tri, etc.
Place the location numbers
of each alkyl group in front of
the name (lowest possible
number)


Small alkanes have very weak London
dispersion forces only (for IM attractions)
and have low BP’s
Longer alkanes have greater London
dispersion forces and have higher BP’s


Natural gas is a fossil fuel composed
primarily of alkanes containing one to
four carbon atoms
Petroleum is a complex mixture of
different hydrocarbons that varies
greatly in composition


Anywhere from 1 to 50 carbon atoms
Petroleum is separated into its different
portions through fractional distillation

When alkanes combust, they
produce carbon dioxide, water,
and heat


The carbon dioxide is a
greenhouse gas
When gasoline ignites before
the flame front reaches it, there
is a decrease in the amount of
power (engine knock)

Octane rating is a measure of the
anti-knocking properties of gs
Unsaturated Hydrocarbons


Unsaturated hydrocarbons are hydrocarbons
in which not all carbon atoms have four single
covalent bonds
Alkenes are hydrocarbons that contain double
covalent bonds


An alkene with one double bond has two less
hydrogens that the corresponding alkane
CnH2n

The rules for naming alkenes are
similar those for naming alkanes




The parent hydrocarbon is the longest
one that contains the double bond
The suffix –ene is added to the prefix
The number are established so that the
first carbon in the double bond has the
lowest number (this number is placed at
the beginning of the name)
If there is more than one double bond, the
suffix is modified to: 2=diene, 3=triene,
etc.


Ethene is the smallest alkene
Ethene is the hydrocarbon
produced in the greatest
quantity in the US


Used in the synthesis of plastic
and alchohol
Can cause the ripening of fruit

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
Hydrocarbons with triple covalent bonds are
alkynes
The general formula is CnH2n-2
The naming rules are similar to the naming
rules for alkenes except the suffix –yne is
used

The smallest
alkyne is ethyne
(acetylene) that is
used for welding
Effusion and Diffusion


Diffusion is the constant motion of gas
molecules that causes them to spread
out in their container
Effusion is the process whereby the
molecules of a confined gas pass
through a tiny opening of their
container

The rates of
effusion and
diffusion depend
on the relative
velocities of gas
molecules

The velocity of a
gas varies
inversely with its
mass (lighter
molecules move
faster than
heavier
molecules at the
same
temperature)
We know that
1 2
KE  mv
2
and since the KE for all gases is
the same at a given temperature
then for gases A & B:
1
1
2
2
M A v A  M B vB
2
2
The M represents the molar mass
1
1
2
2
M A v A  M B vB
2
2
Can be multiplied by 2 to give
M A v A  M B vB
2
And then rearranged to give
2
vA
MB

2
MA
vB
or
vA

vB
MB
MA
2


This leads to
Graham’s law of
effusion which states
that the rates of
effusion of gases at
the same
temperature and
pressure are
inversely proportional
to the square roots of
their molar masses
The law only
provides the relative
rates of effusion
based on the relative
velocities of the
effusion _ rateA

effusion _ rateB
MB
MA
Density varies directly with molar
mass so density can be substituted
for M
densityB
effusion _ rateA

effusion _ rateB
density A
This is used to separate U-238 and U-235
by allowing gaseous uranium to pass
through porous membranes (over time
and many membranes, the U-235
becomes concentrated)