1. Except for hydrogen, the element farther to the left in the periodic table appears first: KCl, PCl₃, Al₂S₃
   
2. If hydrogen is present, it appears last except when the other element is from column VI or VII of the periodic table: LiH, NH₃, CH₄, H₂S, HCl
   
3. If both elements are from the same column of the periodic table, the lower one appears first: SiC, BrF₃

1. We have a formal name for compounds, in our field this is referred to as the IUPAC (International Union of Pure and Applied Chemistry) name
   
2. We have a less formal, but commonly used name
   
3. We also have an informal name which may be used in some circumstances

For example, let's name CH₃CH₂OH

1. IUPAC name ethanol
   
2. Commonly used name ethyl alcohol
   
3. Informal name grain alcohol

1. The element that appears first retains its elemental name
   
2. The second element bears a root derived from its elemental name and ends with the suffix -ide

1. With elements from Groups I and VII, hydrogen forms diatomic molecules according to our earlier guidelines: Thus LiH is Lithium hydride, HCl is Hydrogen Chloride
   
2. With elements from Groups II and VI, hydrogen forms compounds containing two atoms of hydrogen. Except for oxygen, there is only one known binary compound for each element, so the prefix di ­ is omitted: That is why H₂S is not dihydrogen sulfide but is hydrogen sulfide. Oxygen forms two binary compounds with hydrogen and each is known by its informal name. One is water, H₂O, the other is hydrogen peroxide, H₂O₂.
   
3. The systematic approach to chemical nomenclature is abandoned for binary compounds of hydrogen with the elements from Groups III, IV, and V.
    NH₃ is not nitrogen trihydride, it is ammonia
    PH₃ is called phosphine
    AsH₃ is called arsine

4. Carbon, boron, and silicon form many different binary compounds with hydrogen. Binary compounds of silicon and hydrogen are called silanes, binary compounds of boron and hydrogen are called boranes.

The formulas of carbon containing compounds start with carbon, followed by hydrogen. After that, any other elements appear in alphabetical order.
 Examples: C₂H₆O, C₄H₉BrO, CH₃Cl

Isomers­molecules that have the same molecular formula but a different arrangement of atoms.

 Example: C₂H₆O has two isomers:
(CH₃)₂O Dimethyl ether and CH₃CH₂OH Ethanol

• The metals in column I form cations with a +1 charge only
  Li⁺, Na⁺, K⁺, Cs⁺

• The metals in column II form cations with a +2 charge only
  Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺

• Most transition metals can exist in more than one cationic form
  Fe²⁺, Fe³⁺, Cu⁺, Cu²⁺

• Only six elements form stable anions
  F^-, Cl^-, Br^-, I^-, O^2-, S^2-

Ionic compounds also contain clusters of atoms with a net negative charge.
For example: Sodium nitrate NaNO₃ which is Na⁺ + (NO₃)^-
(NO₃)^- is called a polyatomic ion

1. The cation is always listed before the anion
   
2. The formula of any polyatomic ion is written as a unit
   
3. Polyatomic ions are placed in parentheses with a following subscript to indicate ratios different than 1:1

For example:

  Ammonium nitrate
    NH₄⁺ + NO₃^- gives a chemical formula of NH₄NO₃
    note: the compound is neutral and is not written as N₂H₄O₃

  Calcium phosphate
    Ca²⁺ + PO₄^3- gives a chemical formula of Ca₃(PO₄)₂

    Is the compound neutral?
    3 x Ca²⁺ = + 6 charge
    2 x PO₄^3- = - 6 charge
    +6 + -6 = 0, neutral

  Magnesium nitrate
    Mg²⁺ + NO₃^- gives a chemical formula of Mg(NO₃)₂

What do you do when you have a transition metal which can exist in more than one charge state (e.g., Fe²⁺, Fe³⁺)?

  For instance, name these two compounds:
    Cu₂SO₄ and CuSO₄

  So we add one more guideline to solve this problem:
    For any metal that forms more than one stable cation, the charge is specified by using a Roman numeral in parentheses after the name of the metal.

  So back to naming Cu₂SO₄ and CuSO₄

  Cu₂SO₄: What is charge on Copper?
   Remember the compound is electrically neutral and we know the charge for the sulfate group is always 2-, so by charge balance we have:

  2 x (charge on Copper) + (charge on sulfate group) = 0
  2 x (charge on Copper) + (2-) = 0
  2 x (charge on Copper) = 2+
  (charge on Copper) = 1+

    Name is Copper(I) sulfate

  CuSO₄: What is charge on Copper?

    Name is Copper(II) sulfate

Remember, the Roman numeral in the parentheses refers to the charge of the ion not the subscript

Many ionic compounds have water molecules incorporated into their crystalline structures. Such compounds are called hydrates.

  For example: CaCl₂ ^. 6 H₂O; Calcium chloride hexahydrate

A compound is ionic if it contains a metal from column I or column II of the periodic table or one of the polyatomic ions

1. Structural Formulas
   
2. Ball and Stick Models
   
3. Space-Filling Models
   
4. Line Structures

A structural formula not only gives the number of atoms in a molecule but also shows how the atoms are connected to one another.

Atoms are held together by attractive forces called bonds. For now, understand that a chemical bond is formed between a pair of electrons shared between two atoms.

In a structural formula, the bonds between atoms are represented by lines connecting the elemental symbols.

Each line represents one pair of shared electrons. When atoms share one pair of electrons it is called a single bond and we draw a single line.

When atoms share two pairs of electrons, the bond is called a double bond and we draw two lines between the atoms.

By the same analogy, a triple bond is when three pairs of electrons are shared and is represented by three lines between two atoms.

1. All bonds except C ­ H are shown as lines
   
2. C ­ H bonds are not shown in the line structure
   
3. Single bonds are shown as a single line; double bonds are shown as two lines; triple bonds are shown as three lines
   
4. Carbon atoms are not labeled
   
5. All atoms except carbon and hydrogen are labeled with their elemental symbols
   
6. Hydrogen atoms are labeled when they are attached to any atom other than carbon

See the Drawing Line Structures Tutorial for more information.