Overview
This lecture covers the classification of matter, focusing on distinguishing elements and compounds, and provides detailed rules for naming molecular compounds.
Classification of Matter
- Matter is divided into pure substances and mixtures; only pure substances are covered here.
- Pure substances include elements (atomic and molecular) and compounds.
- Most elements are atomic; only seven (H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂) are molecular elements.
Elements: Atomic vs. Molecular
- Atomic elements exist as single atoms (e.g., Na, Fe).
- Molecular elements consist of molecules with two or more of the same atom (e.g., O₂, N₂).
Compounds: Types and Identification
- Compounds are made of atoms from two or more elements.
- Three types: ionic compounds, molecular compounds, and acids.
- Ionic compounds: formed from a metal and a non-metal.
- Molecular compounds: formed from non-metals only.
- Acids: typically start with hydrogen (details covered later).
Determining Compound Type
- Look at the first element:
- If it's a metal, the compound is ionic.
- If both are non-metals, it's molecular.
- In formulas, elements are represented by one uppercase letter (possibly followed by a lowercase letter).
Molecular Compound Naming Rules
- Name the first element as is from the periodic table.
- Change the second element's ending to -ide.
- Use prefixes to show the number of atoms:
- mono- (1), di- (2), tri- (3), tetra- (4), penta- (5), hexa- (6), etc.
- Do not use "mono-" for the first element if there is only one atom.
- Write the prefixes for both elements (except the first if one atom).
Examples of Molecular Compound Names
- CO: carbon monoxide
- CO₂: carbon dioxide
- P₂S₅: diphosphorus pentasulfide
- CCl₄: carbon tetrachloride
- ICl: iodine monochloride
- NO: nitrogen monoxide
- N₂O₅: dinitrogen pentoxide
- SF₆: sulfur hexafluoride
- PCl₃: phosphorus trichloride
- H₂O: dihydrogen monoxide (water)
Key Terms & Definitions
- Element — Pure substance of one kind of atom, atomic or molecular.
- Atomic element — Element existing as individual atoms.
- Molecular element — Element existing as molecules (e.g., O₂).
- Compound — Substance of two or more different atoms bonded together.
- Ionic compound — Compound formed from a metal and non-metal.
- Molecular compound — Compound formed from non-metals.
- Acid — Compound usually starting with hydrogen, details to come.
- Prefix — Word part indicating number of atoms (e.g., di- for 2).
- Nomenclature — System for naming compounds.
Action Items / Next Steps
- Practice naming and writing formulas for molecular compounds.
- Prepare for next class on naming ionic compounds.
- Review periodic table and prefixes for 1–10.