Ionic vs. Molecular Compounds: Naming Conventions

Identifying Ionic vs. Molecular Compounds

• Ionic compounds contain a positively and negatively charged element, typically a metal and a non-metal.
• Ionic compounds involve the giving and taking of electrons, resulting in a neutrally charged compound.
• Molecular compounds typically have prefixes in their names and consist of non-metals only.
• Molecular compounds share electrons and form weak bonds.

Naming Ionic Compounds

• The metal is named first, followed by the non-metal.
• The non-metal's ending is changed to "ide."
• The criss-cross method applies to determine the chemical formula.

Naming Molecular (Covalent) Compounds

• Name the first and second elements.
• The second element's ending changes to "ide."
• Prefixes indicate the number of atoms of each element.
  • Example: Chlorine Pentafluoride = ClF5
• Subscripts in chemical formulas indicate the quantity of each element.

Why Molecular Compounds Need Prefixes

• Prefixes specify the exact number of atoms of each element in molecular compounds.
• Due to the large variety of combinations, prefixes are necessary to clearly define the compound.

Prefixes for Molecular Compounds

• Mono = one
• Di = two
• Tri = three
• Tetra = four
• Penta = five
• Hexa = six

Exception to the "Mono" Prefix Rule

• The prefix "mono" is omitted when the first element has only one atom.
  • Example: Carbon Dioxide (CO2) instead of Monocarbon Dioxide.
  • Example: Dinitrogen Monoxide

Polyatomic Ions

• Polyatomic ions are groups of atoms that act as a single unit.
• Polyatomic ions combine with metals like single atoms.
• The polyatomic ion name typically ends in "ate" instead of "ide."
• When writing chemical formulas, enclose the polyatomic ion in brackets.
  • Example: Mg(CO3)2
  • Example: Hydrogen Oxalate = HOOCCOO-

Groups vs. Periods on the Periodic Table

• Groups are vertical columns (up and down).
• Periods are horizontal rows (side to side).

Common Chemical Formulas

• Table salt: NaCl
• Sugar: C12H22O11
• Rust: Fe2O3
• Water: H2O

Properties of Alkali Metals

• Alkali metals are in the first group (column) of the periodic table (excluding hydrogen).
• Exposure to water can cause explosions.
• They are highly reactive and require special storage.
• Alkali metals readily give off unpaired electrons to form compounds.
• They don't occur freely in nature and are softer than other metals.

Properties of Alkaline Earth Metals

• Alkaline earth metals are in the second group of the periodic table
• They are quite reactive.
• Alkaline earth metals are harder and denser than alkali metals.
• They have higher melting points.
• Alkaline earth metals exhibit stronger metallic bonding due to having two valence electrons.

Properties of Halogens

• Halogens are in the second to last group (column) of the periodic table
• Compounds with halogens are known as "salts."
• Halogens exist in any state of matter at room temperature.

Properties of Noble Gases

• Noble gases are in the last group (column) of the periodic table.
• Noble gases have the maximum number of electrons in their outer shell, making them stable.

Additional Notes

• Reduce ionic compounds to their simplest formulas. (Cl2C4 = ClC2)
• Always enclose polyatomic ions in brackets when writing chemical formulas, as appropriate.
• To find the number of neutrons in an element, subtract the number of protons from the atomic mass (and round to a whole number).
• Remember to reduce formulas.
• Remember to include the "ide" ending unless the compound contains a polyatomic ion.
• Atoms that gain electrons become negatively charged.
• Atoms that lose electrons become positively charged.

Stable vs. Unstable Elements

• Stable elements have a full outer electron shell.
• Stable elements do not need to give or take electrons.
• Unstable elements do not have a full outer electron shell.
• Unstable elements combine with other elements to try to fill their "missing electrons".

Learn to identify and name ionic and molecular compounds based on their composition and bonding characteristics. Understand the rules for naming ionic compounds, including metal/non-metal identification and 'ide' suffix. Explore naming covalent compounds using prefixes to indicate atom quantities.