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 +3Oxide -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 hypo- If 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

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

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)

21

2KE mv

2 21 1

2 2A A B BM v M v

We know that

and since the KE for all gases isthe same at a given temperaturethen for gases A & B:

The M represents the molar mass

2 21 1

2 2A A B BM v M v

Can be multiplied by 2 to give 2 2A A B BM v M v

And then rearranged to give

2

2A B

AB

v M

Mv or

BA

B A

Mv

v M

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 molecules

_

_B

A

Meffusion rateA

effusion rateB M

Density varies directly with molar mass so density can be substitutedfor M

_

_B

A

densityeffusion rateA

effusion rateB density

This is used to separate U-238 and U-235by allowing gaseous uranium to pass through porous membranes (over timeand many membranes, the U-235 becomes concentrated)