Properties of the periodic table

Key properties include:

1. Organization by Atomic Number: Elements are arranged in increasing order of their atomic number (number of protons).
2. Groups (Columns): Vertical columns are called groups (or families). Elements within the same group generally have similar chemical properties because they have the same number of valence electrons.
3. Periods (Rows): Horizontal rows are called periods. Elements within the same period have the same number of electron shells.
4. Periodicity (Trends): Many properties of elements show predictable trends (periodicity) across periods and down groups, such as:
   • Atomic Radius: Generally decreases across a period and increases down a group.
   • Ionization Energy: Generally increases across a period and decreases down a group.
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