Ions, Compounds, and Chemical Formulas Explained

Posted on Feb 10, 2025 in Chemistry

Ions: Charged Particles

Ion: A charged particle composed of an atom that has gained or lost electrons. Atoms are neutral.

Cations: Positive Ions

Cation: A positively charged ion due to the loss of electrons from a neutral atom (e.g., Na⁺).

Anions: Negative Ions

Anion: A negatively charged ion due to an increase in the number of electrons (e.g., Cl^–).

Chemical Compounds and Formulas

Ionic Compound: Formed by cations and anions. Ionic compounds are composed of electrically charged particles, while molecular compounds are composed of neutral particles.

• Monatomic: 1 atom
• Diatomic: 2 atoms
• Polyatomic: 2 or more atoms

Chemical Formulas: Express the composition of molecules and ionic compounds through chemical symbols.

Molecular Formula: Indicates the exact number of atoms of each element present in the smallest unit of a substance.

Allotrope: One of two different forms of an element (e.g., O₂, O₃).

Empirical Formula: Indicates which elements are present and the minimum whole number ratio among its atoms. EXAMPLE: N₂H₄ in empirical formula -> (NH₂)

Organic and Inorganic Compounds

Organic Compounds: Contain carbon, usually combined with elements such as hydrogen, oxygen, nitrogen, and sulfur. Compounds with carbon that actually belong to inorganic compounds are carbon monoxide, carbon dioxide, carbon disulfide, compounds containing the cyanide group, as well as carbonate and bicarbonate groups.

Inorganic Compounds: All other compounds. Ionic compounds are formed by cations and anions. Ammonium ion is an exception to all the cations of interest arising from metal atoms. Metal cations are named after the element. Example:

Binary Compound: Consisting of only two elements.

Ternary Compound: Compound formed by three elements.

Naming Chemical Compounds

Extra Information: Transition metals are the elements of groups IB and IIIB to VIIIB. Oxidation numbers represent the apparent charge on an atom.

The anion (e.g., NaCl) is named by taking the first part of the name of the element (chlorine) and adding the suffix “ide” (sodium chloride). These are binary compounds.

Stock Naming System

Stock Naming System: Basic metal oxide + oxidation number of the metal written in Roman numerals.

Molecular Compounds

Molecular Compounds: Composed of discrete molecular units. Binary molecular compounds are named by first naming the second element in the formula and adding “ide” to the root of the element’s name, followed by the first element. Example: HCl – hydrogen chloride, SiC – silicon carbide. It is very common for a pair of elements to form several different compounds. In these cases, confusion is avoided by naming compounds using Greek prefixes (CO – carbon monoxide, CO₂ – carbon dioxide, SO₃ – sulfur trioxide).

The exception to the use of Greek prefixes is in the case of molecular compounds containing hydrogen. Traditionally, these compounds are called by their common names or by non-systematic names that do not indicate the number of H atoms present: (B₂H₆ – diborane, CH₄ – methane, SiH₄ – silane, NH₃ – ammonia, PH₃ – phosphine, H₂O – water, H₂S – hydrogen sulfide)

Hydrides, Oxides, Hydroxides, and Acids

Hydride: Any combination of an element with hydrogen (e.g., NaH – sodium hydride).

Oxide: Binary combination of an element with oxygen (e.g., CaO – calcium oxide).

Hydroxide or Base: Any substance that can accept a hydrogen ion or react with an acid. Bases are named with the word hydroxide followed by the name of the metal (e.g., NaOH – sodium hydroxide).

Acid: An acid can be described as a substance releasing hydrogen ions (H⁺) when dissolved in water. Acids have a sour taste, can cause color changes in plants, and interact with certain metals such as zinc, magnesium, or iron to produce hydrogen gas. Anions whose names end in “ide” form acids whose names end in “hydro…ic acid”. Example:

Salts

Salt: Product of the reaction between an acid and a base (base + acid = salt + water) (e.g., NaOH + HCl = NaCl + H₂O).