Molecules and Compounds Unit Naming2

Molecules and Compounds Unit Naming2

Some key terminology you must keep in mind while completing this section of study:

Atom – the smallest particle of an element that retains all the properties of that element; is electrically neutral, spherically shaped, and composed of electrons, protons, and neutrons.

Ion – an atom or bonded group of atoms with a negative or positive charge.

Polyatomic ions – an ion made up of two or more atoms bonded together that acts as a single unit with a net charge.

Molecules – forms when two or more atoms covalently bond and is lower in potential energy than its constituent atoms.

Compound – a chemical combination of two or more different elements; can be broken down into simpler substances by chemical means and has properties different from those of its component elements.

We need to remember the basic about the periodic table and how to determine ionic charges based on what is on the table, as well as learning about the polytomic ions.

Determining Charge

A monatomic ion is a one-atom ion, such as Mg2+ or Br-. The chart below indicates the charges of common monatomic ions according to the location of their atoms on the periodic table. Transition metals, which are in groups 3-12, and metals in groups 13 and 14 are not included in this table because of the variance in ionic charges of atoms in the group. Most transitional metals and those in groups 13 and 14 can form several different positive ions.

Common Ions Based on Groups
Group / Atoms that commonly form ions / Charge on ions
1 / H, Li, Na, K, Rb, Cs / 1+
2 / Be, Mg, Ca, Sr, Ba / 2+
15 / N, P, As / 3-
16 / O, S, Se, Te / 2-
17 / F, Cl, Br, I / 1-

The charge of a monatomic ion is its oxidation number. Most transition metals and group 13 and 14 metals have more than one oxidation number. The oxidation numbers given in the following table are the most common ones for many of the elements listed but might not be the only ones possible.

Common Ions of Transition Metals and Groups 13 and 14
Group / Common Ions
3 / Sc3+, Y3+, La3+
4 / Ti2+, Ti3+
5 / V2+, V3+
6 / Cr2+, Cr3+
7 / Mn2+, Mn3+, Tc2+
8 / Fe2+, Fe3+
9 / Co2+, Co3+
10 / Ni2+, Pd2+, Pt2+, Pt4+
11 / Cu+, Cu2+, Ag+, Au+, Au3+
12 / Zn2+, Cd2+, Hg2+
13 / Al3+, Ga2+, Ga3+, In+, In2+, In3+, Tl+, Tl3+
14 / Sn2+, Sn4+, Pb2+, Pb4+

The term oxidation state is sometimes used and means the same thing as oxidation number. The oxidation number, or oxidation state, of an element in an ionic compound equals the number of electrons transferred from an atom of the element to form the ion. For example, when sodium and chlorine atoms react, the sodium atom transfers one electron to the chlorine atom, forming Na+ and Cl-. In the compound formed, the oxidation state of sodium is 1+ because one electron is transferred from the sodium atom. The oxidation state of chlorine is 1-. One electron is transferred and the negative sign shows that the electron transferred to, not from the chlorine atom.

Compounds that contain polyatomic ions

The charge given to a polyatomic ion applies to the entire group of atoms. Although an ionic compound containing one or more polyatomic ions contains for than two atoms, the polyatomic ion acts as a individual ion. Therefore, the chemical formula for the compound can be written following the same rules used for a binary compound. Because a polyatomic ion exists as a unit, never change subscripts of the atoms within the ion. If more than one polyatomic ion is needed, place parentheses around the ion and write the appropriate subscript outside the parentheses. For example, the formula for magnesium chlorate is Mg(ClO3)2. Note that the ammonium ion is the only common polyatomic cation. The following chart lists the Common Polyatomic Ions.

Common Polyatomic Ions
Ion / Name / Ion / Name
NH4+ / Ammonium / IO4- / Periodate
NO2- / Nitrite / C2H3O2- / Acetate
NO3- / Nitrate / H2PO4- / Dihydrogen phosphate
HSO4- / Hydrogen sulfate / CO32- / Carbonate
OH- / Hydroxide / SO32- / Sulfite
CN- / Cyanide / SO42- / Sulfate
MnO4- / Permanganate / S2O32- / Thiosulfate
HCO3- / Hydrogen carbonate / O22- / Peroxide
ClO- / Hypochlorite / CrO42- / chromate
ClO2- / Chlorite / Cr2O72- / Dichromate
ClO3- / Chlorate / HPO42- / Hydrogen phosphate
ClO4- / Perchlorate / PO43- / Phosphate
BrO3- / Bromate / AsO43- / Arsenate
IO3- / Iodate

Please be sure to get a copy of the polyatomic ion table.

Classification of Compounds

Compounds are classified based on the atoms that compose them. The IUPAC (International Union of Practical and Applied Chemistry) has designed a naming scheme for each compound group.

The following chart illustrates how we might subdivide the compounds for the purpose of naming them.

Compounds
Covalent
(contain nonmetal atoms combining with other nonmetal atoms) / Ionic
(contain a metal or NH4 + ion)
Binary Molecular
contain only two nonmetal atoms / Hydrocarbons
contain hydrogen and carbon atoms only
. / Acids
contain nonmetal atoms with hydrogen written first / Ammonium Compounds
contain NH4 + ion / Monovalent Ionic Compound
contain metal ions with only one charge / Divalent Ionic Compounds
contain metal ions with two possible different ions

Binary Molecular Compounds

Binary molecular compounds contain only two nonmetals.

To Name:

·  The first atom is named in full

·  The second atoms name is shortened and -ide added.

·  The prefixes below are added to the first and second name to indicate the number of atoms present in the compounds.

·  The prefix mono is typically not placed on the first atoms name.

# of Atoms / Prefix / # of Atoms / Prefix
1 / mono- / 6 / hexa-
2 / di- / 7 / hepta-
3 / tri- / 8 / oct-
4 / tetra- / 9 / non-
5 / penta- / 10 / dec-

Examples:

P2O5 diphosphorus pentaoxide

CO2 carbon dioxide

Hydrocarbons(straight chained)

Hydrocarbons are compounds that contain only carbon and hydrogen.

To Name:

·  The first part of the name is a prefix that indicates the number of carbon atoms. The prefixes are the same as those used by Binary Molecular compounds above except for the first four. These four are:

# of Carbon Atoms / Prefixes
1 / meth -
2 / eth -
3 / prop -
4 / but -

·  The second part of the name is a suffix that describes if the compound contains single bonds, a double or a triple bond between the carbon atoms. The following table illustrates the naming and gives examples.

· 

Group / Bonds between carbons / Suffix / Ratio of Carbon to Hydrogen / Example / Name
Alkane / all single / - ane / CnH2n+2 / C3H8 / propane
Alkene / one double / - ene / CnH2n / C4H8 / butene
Alkyne / one triple / - yne / CnH2n-2 / C5H8 / pentyne

Acids

Acids are substances formed when nonmetal ions combine with hydrogen. The hydrogen is written first in the compound and the naming is based on whether the anion (negative ion) is:

·  simple

·  polyatomic.

1. To Name Acids with Simple Anions: (using a table of ions)

·  The first part of the name is the prefix hydro.

·  This is followed by a the name of the simple anion, which is shortened and - ic added

o  for example chlorine (Cl-) would become chloric

·  The last part of the name is the word acid

Acid / Ion / Name
HF / F- / Hydrofluoric Acid
HI / I- / Hydroiodic Acid

2. To Name Acids with polyatomic anions: (using a table of ions)

·  The first part of the name is the name of the anion which is shortened . One of two suffixes added to this name.

o  - ic if the anion name ends in - ate.

o  - ous if the anion name ends in - ite.

·  The last part of the name is acid

Acid / Ion / Name
H2SO4 / SO4 2- / sulfuric acid
(anion, sulfate)
HClO3 / ClO3 - / perchlorous acid
(anion, perchlorite)

3. To determine an acid formula from a name (Using a table of ions ) we:

1.  Determine the anion present from the name.

2.  Since the compound is an acid the cation ( positive ion ) is H +

3.  Write down the formulas of the two ions . Make the value of the charge on the negative ion the subscript on the hydrogen ion

Example:

Sulfuric Acid

·  sulfuric ------> sulfate ------> SO4 2-

·  acid ------> hydrogen ------> H +1

·  Formula ------> H2SO4

Naming ionic compounds

Ionic Compounds contain a metal or the ion NH4 +1. All ionic compounds are named by listing the names of the two ions that are present. Formulas for ionic compounds are termed empirical. This means that the ions are always listed in the simplest ratio. In any ionic compound:

the total charge on the cation is equal and opposite to the total charge on the anion.

This concept is illustrated in the table below

Formula / Ions charge / Number of ions present / Total charge
Ca3(PO4)2 / Ca 2+ / 3 / + 6
PO4 3- / 2 / - 6

·  All ionic compounds contain a cation (ion with positive charge) and an anion (ion with negative charge)

·  Ions (both anions and cations) can be either simple (one atom ions) or complex (polyatomic ions).

The ionic compounds can be broken into three groups, in order to name them.

Ammonium (NH4 +) compounds

Ammonium compounds contain the complex cation NH4 +1.

1. To Name: (using a table of ions)

·  The first part of the name is Ammonium

·  Second part of name is the name of the anion.

Formula / Name
(NH4)2SO4 / Ammonium sulfate
(NH4)3PO4 / Ammonium phosphate

2. To determine formula from name

·  Using a table of ion determine the two ions that are present , the positive ion is NH4 + and then the anion.

·  The subscript for the NH4 +1 ion in the formula will be the charge on the anion and the subscript for the anion will be one.

For example: Ammonium carbonate

Ions present / NH4 +1 / CO3 2-
Cross over charges to determine formula / (NH4)2CO3

Monovalent Cations

Ionic compounds containing monovalent cations (cation with one charge) are named by simply listing the name of the cation and the name of the anion.

1. To Name (using a table of ions):

·  Locate the name of the metal cation (positive ion). Make sure it has only one charge.

·  Locate the name of the anion.

·  Place names together.

Formula / Name
AgCl / Silver chloride
Mg(NO3)2 / Magnesium nitrate

2. To determine the formula from name: (using table of ions)

·  locate the cation and anion in a table of ions and write down the formula for each.

·  Make the value of the charge for the cation the subscript for the anion and visa versa. (cross over value of charges)

·  simplify the formula to the simplest ratio of the ions. See table below (this is called an empirical formula)

·  if there is more than one complex ion needed in the formula then a bracket is placed around the ions and subscript used to indicate the number of ions needed. (see table below)

Name / Ions charge / Formula / Empirical
Magnesium Oxide / Mg 2+ / Mg2O2 / MgO
O 2 -
Aluminum carbonate / Al 3+ / Al2(CO3)3 / Same
CO3 2-

Divalent cations

Ionic compounds containing divalent cations (metal ions with two possible charges) can be named in two ways

1.  Using the Stock system ( Roman Numerals )

2.  Using the Classical system ( suffix - ic and - ous.)

A. Stock system:

o  developed by Alfred Stock . This method places a Roman Numerals in brackets behind the name of the cation.

o  The Roman Numerals is equal in value to the charge on the cation.

Cation / Name
Sn 4+ / Tin (IV)
Cu+ / Copper (I)

1. To Name using Stock system given the formula:

o  Locate the name of the anion and cation in a table of ions.

o  Using the concept that the total charge of the anion and cation must be equal we can determine what the charge on the cation must be. ( anion charges are always fixed.) See example below

· 

Formula / Charge on Anion / Total charge on anion / Total charge on Cation / Number of Cation / Charge on Each Cation
Fe2O3 / O 2- / - 6 / +6 / 2 / +3

·  The name of the example above would be: Iron (III) oxide

To determine name then we: (using a table of ions)

1.  Name the cation

2.  Determine the charge on the cation using the method above.

3.  Apply the correct Roman Numerals

4.  Finally name of the anion.

Formula / Name of Cation / Total Charge on Anion / Total charge on Cation / Charge on Cation / Name
Cu2O / Copper / -2 / +2 / +1 / Copper (I) oxide
CrCl3 / Chromium / -3 / +3 / +3 / Chromium (III) chloride

2. To determine formula from name. See monovalent cations

B. Classical System:

·  Uses Latin and English names for metal cations

·  Uses the suffixes - ic and - ous to distinguish between the larger and smaller charges on the two ions.

·  Used less often than the Stock system .

1. To Name using the Classical System: (using a table of ions)

·  Same procedure is followed to determine the ion charge, that was used with the Stock System.

·  If the cation is the larger of the two possible divalent cations it's Latin or English name is shortened and - IC added.