Overview
This lecture covers the basics of elements and compounds, their classification, naming conventions, and the organization of the periodic table, including key properties and examples.
Elements and Their Symbols
- Elements are pure substances that cannot be broken down by chemical means.
- Each element is made up of atoms, the smallest unit involved in chemical reactions.
- Elements are represented by symbols; one letter (uppercase) or two letters (first uppercase, second lowercase).
- Some element symbols are based on Latin or Greek names (e.g., Na for sodium from "natrium").
- Correct capitalization of symbols is important (e.g., Co is cobalt, CO is carbon monoxide).
The Periodic Table and Classification
- Elements are organized in the periodic table by increasing atomic number.
- Vertical columns are called groups; horizontal rows are called periods.
- General classification: metals, non-metals, and metalloids (semi-metals).
- Metals: mostly solids, shiny, good conductors of electricity.
- Non-metals: often gases or liquids, dull, poor conductors.
- Metalloids have properties between metals and non-metals.
- Majority of elements are metals, found on the left; non-metals on the right; metalloids form a "staircase" in between.
Group-wise Classification
- Main groups to know:
- Group 1: Alkali metals (very reactive)
- Group 2: Alkaline earth metals
- Group 17: Halogens
- Group 18: Noble gases (inert/unreactive)
- Transition metals are located in the center of the table.
- Atomic number increases left to right across periods.
Diatomic Elements and Compounds
- Seven elements exist naturally as diatomic molecules: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂.
- Compounds are formed by combining atoms of different elements in fixed ratios.
- Example: Water (H₂O) has two hydrogen atoms and one oxygen atom.
Types of Compounds
- Ionic compounds: formed from metals and non-metals (e.g., NaCl).
- Molecular compounds: formed from only non-metals or non-metals and metalloids (e.g., H₂O).
- Molecule: two or more atoms bonded together.
- Diatomic molecule: two atoms of the same or different elements bonded together.
Naming and Writing Formulas
- Write the element symbol with the number of atoms as a subscript (e.g., CO₂: one carbon, two oxygen).
- For groups of atoms (polyatomic ions), parentheses and subscripts are used (e.g., Ca(NO₃)₂).
- Do not write "1" as a subscript; it is understood.
Ions
- Ions are atoms or groups of atoms with a charge.
- Cations: positively charged ions.
- Anions: negatively charged ions.
Key Terms & Definitions
- Element — a pure substance that cannot be broken down by chemical means.
- Atom — the smallest unit of an element.
- Compound — a substance made from two or more elements chemically bonded.
- Periodic Table — a chart organizing elements by increasing atomic number.
- Group — vertical column in the periodic table.
- Period — horizontal row in the periodic table.
- Metal — element, usually solid and conductive.
- Non-metal — element, often gas or liquid, non-conductive.
- Metalloid — element with properties of both metals and non-metals.
- Diatomic molecule — molecule with two atoms (e.g., O₂).
- Ion — atom or group of atoms with a positive or negative charge.
- Cation — positively charged ion.
- Anion — negatively charged ion.
Action Items / Next Steps
- Review periodic table and memorize symbols for common elements.
- Practice writing and identifying element names and symbols.
- Complete provided practice problems on element classification and formulas.
- Follow class schedule and stay current with assigned readings and homework.