Overview
This lecture explains the structure and logic of the periodic table, including how elements are organized and the significance of groups and periods.
Mendeleev and the Periodic Table
- Dmitri Mendeleev created the periodic table in the 19th century.
- His table organized elements by increasing atomic number and predicted undiscovered elements.
Structure of the Periodic Table
- The table is read left to right and top to bottom by increasing atomic number (number of protons).
- Each box includes the element symbol, atomic number (bottom left), and mass number (top left).
Groups and Periods
- Elements are arranged in rows (periods) and columns (groups) based on repeating chemical property patterns.
- Each period starts a new row when chemical properties repeat.
- Columns (groups) contain elements with similar chemical properties.
Group Number Significance
- Group number shows how many electrons are in the element’s outer shell.
- All elements in a group have the same number of outer shell electrons, giving similar properties.
Specific Groups
- Group 1 (alkali metals): one outer electron; very reactive, especially with water.
- Group 2: two outer electrons; similar chemical behaviors within the group.
- Group 7 (halogens): seven outer electrons; reactivity decreases down the group.
- Group 0 (noble gases): full outer shells; very unreactive.
Metals, Nonmetals, and Transition Metals
- A zig-zag line separates metals (left) from nonmetals (right).
- Most elements are metals.
- Transition metals are located in a block between groups 2 and 3.
Using Different Periodic Tables
- Periodic tables may vary in layout, but always display atomic number and mass number.
- The atomic number is always the smaller number.
Key Terms & Definitions
- Atomic Number — number of protons in an atom.
- Mass Number — total number of protons and neutrons in an atom.
- Group — vertical column; elements have same number of outer shell electrons.
- Period — horizontal row; elements arranged by increasing atomic number.
- Noble Gases — Group 0 elements with full outer electron shells; unreactive.
- Alkali Metals — Group 1 elements; highly reactive metals.
Action Items / Next Steps
- Review groups 1, 7, and 0, and the differences between metals and nonmetals in future sessions.
- Practice identifying atomic number and mass number on different periodic tables.