Naming Binary Compounds

Naming Binary Compounds

Introduction

• A binary compound is a chemical made of two different elements.

• Naming binary compounds is the first step in learning to name any chemical.

• This video covers naming:

  • Simple ionic compounds

  • Multivalent ionic compounds

  • Simple covalent compounds

• The video does not cover polyatomic ions or organic compounds.

General Rules

• The more metallic or less electronegative element is written first in both the chemical name and formula (e.g., CaCl_2).

• The metallic nature of an element can be determined by its position on the periodic table.

  • Metals are typically to the left and towards the bottom of the periodic table.

• The first element's name remains unchanged, while the ending of the second element changes to "ide".

  • Example: Calcium chloride (CaCl2) and Carbon dioxide (CO2).

Ionic vs. Covalent Compounds

• Ionic compounds:

  • Typically made of a metal and a nonmetal (e.g., calcium chloride).

  • Do not use prefixes.

• Covalent compounds:

  • Composed of only nonmetals or metalloids (e.g., carbon dioxide).

  • Use prefixes to indicate the numbers in the formula.

Naming Covalent Compounds

• Common prefixes for covalent compounds:

  • 1: mono

  • 2: di

  • 3: tri

  • 4: tetra

  • 5: penta

  • 6: hexa

  • 7: hepta

  • 8: octa

  • 9: nona

  • 10: deca

• The "mono" prefix is not used for the first element (e.g., CO_2 is carbon dioxide, not monocarbon dioxide).

• Mono is used for the second element (e.g. N_2O is dinitrogen monoxide).

• An 'a' or 'o' at the end of a prefix is dropped if followed by 'oxide' (e.g., P2O4 is diphosphorus tetroxide, not diphosphorus tetraoxide).

  • Example: B2S3 is diboron trisulfide.

  • Example: Arsenic pentachloride is AsCl_5.

Naming Ionic Compounds

• Ionic compounds generally do not use prefixes (e.g., Li3N is lithium nitride, Al2S_3 is aluminum sulfide).

• The octet rule helps determine the formula from the name.

  • Main group elements tend to gain or lose electrons to have the same number of electrons as the nearest noble gas (typically 8 valence electrons).

  • Elements with 1, 2, or 3 valence electrons lose them, resulting in +1, +2, and +3 charges, respectively.

  • Nonmetals like nitrogen, oxygen, and fluorine gain electrons to achieve 8 valence electrons, resulting in -3, -2, and -1 charges, respectively.

• All compounds need to be neutral, so the charges of the ions must balance.

  • Example: Magnesium fluoride. Magnesium (Mg) is in column 2, so it forms Mg^{2+} ions. Fluorine (F) is in the next to last column, so it forms F^- ions. Therefore, the formula is MgF_2.

• The magnitude of one ion's charge becomes the subscript of the other element.

  • Example: Aluminum oxide. Aluminum ions have a +3 charge (Al^{3+}), and oxide ions have a -2 charge (O^{2-}). So, the formula is Al2O3.

• Reduce the ratio to the smallest whole numbers for ionic compounds.

  • Example: Calcium sulfide. Calcium ions have a +2 charge (Ca^{2+}), and sulfide ions have a -2 charge (S^{2-}). The initial formula would be Ca2S2, but it reduces to CaS.

Multivalent Ionic Compounds

• Transition metals (and some others) can form more than one stable ion (multivalent ions).

• Roman numerals indicate the charge of the metal ion.

  • Example: Iron can form Fe^{2+} and Fe^{3+} ions. FeCl2 is iron(II) chloride, and FeCl3 is iron(III) chloride.

• To name these compounds, calculate the total negative charge of the anions and then determine the charge of the metal cation.

  *Example: Copper (I) phosphide
  Copper (I) has a positive one charge, so that's CU^+.
  Phosphorus has five valence electrons, so it will gain three electrons to make phosphide which is P^{3-}.
  The formula is Cu_3P

  • Example: CrBr_3. Bromide has a -1 charge, and there are three bromides, so the total negative charge of the anions is -3. Therefore, chromium must have a +3 charge. The name is chromium(III) bromide.

Practice Problems

1. Li_3N - Lithium nitride (simple ionic compound)

2. CCl_4 - Carbon tetrachloride (covalent compound)

3. MnO_2 - Manganese(IV) oxide (multivalent ionic compound)

4. Iodine and barium - BaI_2 Barium Iodide (simple ionic compound)