Chapter 6 Chemical Names and Formulas

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Molecular Vs. Ionic Compounds

Molecular compounds – generally composed of two or more nonmetals. Tend to have low melting and boiling points, dissolve easily, generally poor conductors or electricity. Its’ representative unit is the molecule.

Ionic compounds – composed of ions. (Ions are atoms or groups of atoms that carry a charge. Ions form when an atom or group of atoms lose or gain electrons.) Ionic compounds are generally composed of a metal cation (+ion) and a nonmetal anion (- ion) in that order. Tend to have high melting points and are generally good conductors of electricity. Its’ representative unit is the formula unit.

Chemical Nomenclature – a chemical formula shows the kinds and numbers of atoms in the smallest representative unit of the substance.

Monatomic (single atom) – He, Ne

Diatomic molecules have two atoms of the same element and use a subscript of 2 to show this. Br₂ I₂ N₂ Cl₂ H₂ O₂ F₂

Binary Molecular Compounds – composed of two nonmetals. Prefixes are used. (P. 159) mono-1, di-2, tri-3, tetra-4, penta-5, hexa-6, hepta-7, oxta-8, nona-9, deca-10.

To write the name of a binary molecular formula:

1^st name is the name of the first element with the prefix for its’ subscript (mono is omitted)

2^nd name is the name of the second element with and –ide ending and with the prefix for its’ subscript.

Ex. CO₂ : Carbon dioxide : NO CHARGES USED

SO₃ : Sulfur trioxide : NO METALS

Cl₂O₈ : Dichlorine octoxide : NO CRISS CROSS

XeF₄ : Xenon tetraflouride : NO REDUCING

Naming and Writing Ionic Compounds

Since made up of a cation (+ ion) and an anion (- ion), you must learn all the lists of possible ions and their names.

1^st name = name of cation; 2^nd name = name of anion.

Representative elements – use column on periodic chart to help remember charges.

IA = 1+, IIA = 2+, IIIA = 3+, VA = 3-, VIA = 2-, VIIA = 1- (for the most part: IB = 1+, IIB = 2+)

To name these ions, the positive ions are just the name of that element, but to name the negative ions you must change the ending to –ide.

Transition elements and a few others tend to have multiple charges and must be memorized. (Look on list given and use memory aid to help memorize it) (P. 144)

Polyatomic ions – group of atoms that act as a unit and carry a charge (radicals or packages). Notice that –ite ending has one less oxygen that –ate ending. (P. 147) Found in ternary ionic compounds.

Writing ionic compound formulas (use criss cross method for balancing ions) First write the cation symbol then the anion symbol. If the charges do not cancel out, do second step. Second, take the numbers only from the charges and bring them down diagonally as a new subscript. If there is already a subscript there put the ion in parenthesis before bringing the subscript down. This causes the compound to be balanced or electrically neutral. Reduce if needed.

EX. Calcium phosphide Ca²⁺ P^3- : Ca₃P₂

Ammonium phosphate NH₄⁺ PO₄^3- : (NH₄)₃PO₄

Calcium carbonate Ca²⁺ CO₃^2- : CaCO₃

Lead(IV) sulfate Pb⁴⁺ SO₄^2- : Pb(SO₄)₂

Naming Common Acids- most common definition of acids are compounds that produce hydrogen ions when dissolved in water. Formulas tend to start with the H ion. (For rules refer to Ch.20.1 for notes)

Know these common acids:

Hydrochloric Acid : HCl

Sulfuric Acid : H₂SO₄

Nitric Acid : HNO₃

Acetic Acid : HC₂H₃O₂

Phosphoric Acid : H₃PO₄

Carbonic Acid : H₂CO₃

Law of Definite Proportions – in samples of any chemical compound, the masses of the elements are always in the same proportions.

Law of Multiple Proportions – whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.