4.6-4.8 Ionic Compounds and Nomenclature, Molecular Compounds and Nomenclature

formula unit

the lowest whole-number ratio of ions in an ionic compound that gives an overall neutral charge (NaCl, K₂O, AgNO₃)

are ionic compounds made of molecules?

NO

ionic compounds are electrically _______

NEUTRAL

because ionic compounds are electrically neutral, that means the sum of all the POSITIVE CHARGE is _____ ___ the sum of all the NEGATIVE CHARGE

EQUAL TO

ionic compounds vs molecular compounds

nonmetal+metal (transfer electrons) vs nonmetal+nonmetal (share electrons)

naming ionic compound direction

name the cation and then the anion

Monatomic Cations

elements whose ion charges are either predictable or unpredictable

elements whose ion charges are PREDICTABLE

Parent atom name + “ion”

Ex: Strontium ion 2A = Sr²⁺

Transition Metal Exceptions

Zn²⁺, Sc³⁺, Ag⁺

Elements whose ion charges are NOT PREDICTABLE

Charge is NOT predictable from Group Number and CAN VARY (can form more than 1 type of ion)

Parent atom name + charge in roman numerals + “ion”
Ex: Chromium + II + 2+ = Cr²⁺

Polyatomic Cations

2 or more atoms bound together acting as a single unit with a net positive charge

Ex: NH₄⁺ ammonium ion, H₃O⁺ hydronium ion, Hg₂²⁺ mercury (I) ion

monatomic anions

Main group elements whose ion charges are predictable - maingroup nonmetals in Groups 5A, 6A, 7A

naming monatomic anions

name of parent atom base + “-ide” + ion
Ex: Fluorine: Fluor + -ide + 1- = F^-

Polyatomic Ions (mostly Anions)

Bonding within the ion is covalent
Many names end in “-ate” or “-ite”

Oxyanions

polyatomic ions with oxygens bound to other elements

The “-ate” vs “-ite” rule

“-ate” = base form for the most common oxyanion in a series (Nitrate NO₃^-)
“-ite” = always has 1 less oxygen atom than the "-ate" form, but maintains the exact same charge (Nitrite NO₂^-)

The Halogen Pattern - “per-” and “hypo-”

Oxyanions with More Than 2 Forms use prefixes “per-” and “hypo-”

Adding Hydrogen (H⁺)

When a hydrogen ion (H⁺) attaches to an oxyanion, it reduces the overall negative charge by 1 for every hydrogen added
Phosphate PO₄^3- —> Hydrogen phosphate HPO₄^2- (-3 + 1 = -2)

Polyatomic Ions to Memorize

Acetate C₂H₃O₂^-
Carbonate CO₃^2-
Hydroxide OH^-
Nitrate NO₃^-
Phosphate PO₄^3-
Ammonium NH₄⁺
Chlorate ClO₃^-
Perchlorate ClO₄^-
Permanganate MnO₄^-
Sulfate SO₄^2-
Cyanide CN^-

Hydrates

ionic compounds in which the formula unit has a certain number of water molecules weakly associated/bounded with it

[ionic compound name] • [Greek Prefix]hydrate
ex: MgSO₄ • 7H₂O = Magnesium Sulfate heptahydrate (7 waters)

Binary Molecular Compounds

molecules formed by 2 different nonmetal elements

Naming Binary Molecular Compounds Steps

1. Name the First Element First: Use the full element name. Add a Greek prefix only if there are 2 or more atoms. Never use "mono-" on the very first element.

2. Name the Second Element with "-ide": Change the ending of the second nonmetal to "-ide" and always include a Greek prefix to show how many atoms are present.

3. Drop Clashing Vowels: If a prefix ends in an "a" or an "o" (like mono- or tetra-) and the element starts with an "o" (like oxide), drop the vowel at the end of the prefix to make it easier to pronounce (e.g., monoxide instead of monooxide, tetroxide instead of tetraoxide).

Example: N₂O₄ = Dinitrogen Tetroxide