Overview
This lecture explains the structure and use of the periodic table, describes elements, and introduces how to classify elements as metals, non-metals, and semimetals.
Atoms and Elements
- Everything is made of tiny particles called atoms.
- There are 92 naturally occurring types of atoms, each forming a different element.
- An element contains only one kind of atom (e.g., a nugget of pure gold is only gold atoms).
The Periodic Table
- The periodic table lists all known elements from lightest (hydrogen) to heaviest (uranium and beyond).
- Each element has a unique symbol (one or two letters) and an atomic number.
- The periodic table has seven horizontal rows and 18 vertical groups (columns).
- Rows are called periods; columns are called groups or families.
- Lanthanides (elements 57–71) and actinides (elements 89–103) belong in periods 6 and 7.
- Scientists have created artificial elements beyond uranium, leading to 118 known elements.
Navigating the Periodic Table
- Example: Element with atomic number 30 is zinc; calcium's atomic number is 20.
- Elements in the same group share similar properties.
- Group 1: Alkali metals, Group 2: Alkaline earth metals, Group 17: Halogens, Group 18: Noble gases.
- Each element is uniquely identified by its period (row) and group (column).
Metals, Non-Metals, and Semimetals
- A diagonal band divides metals (left) and non-metals (right).
- Metals are shiny, good conductors of electricity and heat, and malleable (flatten into shape).
- Most metals are solid, except for liquid mercury.
- Non-metals are usually gases or brittle solids, and poor conductors.
- Semimetals (metalloids) have properties between metals and non-metals (e.g., silicon is shiny but brittle and a semiconductor).
- About three-fourths of elements are metals, but non-metals like oxygen and silicon are more abundant in Earth's crust.
Special Cases
- Hydrogen is unique: placed left on the table but is not a metal or part of any group.
Key Terms & Definitions
- Atom — The smallest unit of an element, retaining its properties.
- Element — Substance made of only one kind of atom.
- Periodic Table — Organized list of all known elements by increasing atomic number.
- Symbol — One or two letter abbreviation for an element.
- Atomic Number — Number indicating an element's position, equal to its protons.
- Group — Vertical column on the periodic table containing elements with similar properties.
- Period — Horizontal row on the periodic table.
- Metal — Shiny, conductive, malleable element, usually solid.
- Non-metal — Poor conductor, brittle, often gaseous element.
- Semimetal (Metalloid) — Element with properties between metals and non-metals.
- Semiconductor — Material that partially conducts electricity, typical of metalloids.
Action Items / Next Steps
- Obtain and study a periodic table for reference.
- Practice identifying elements by symbol, atomic number, group, and period.
- Review the properties of metals, non-metals, and metalloids.