The periodic table organizes the elements by atomic structure so that chemical properties and trends are visible at a glance.
How to Read an Element Box
Each element box typically contains:
- Atomic Number (top) — number of protons
- Element Symbol — one or two letter abbreviation (e.g., Fe for Iron)
- Element Name — full name
- Atomic Mass (bottom) — weighted average mass in atomic mass units (amu)
Example: Carbon (C)
- Atomic Number: 6 (6 protons, 6 electrons)
- Atomic Mass: 12.011 amu
- This means carbon has 6 protons and typically 6 neutrons
Periods (Rows)
The periodic table has 7 periods (horizontal rows). As you move down a period:
- Elements gain more electron shells
- Atomic radius increases
- Ionization energy generally decreases
- Elements become more metallic
Groups (Columns)
Elements in the same group share similar chemical properties because they have the same number of valence electrons.
Key Groups
| Group | Name | Properties |
|---|---|---|
| 1 | Alkali Metals | Soft, highly reactive, one valence electron |
| 2 | Alkaline Earth Metals | Reactive, two valence electrons |
| 17 | Halogens | Very reactive nonmetals, one electron short of full shell |
| 18 | Noble Gases | Unreactive, full outer electron shell |
Transition Metals (Groups 3-12)
These form the large central block. They're typically hard, dense, and good conductors. Many form colorful compounds (copper → blue/green, iron → rust red).
Periodic Trends
Understanding trends helps you predict element behavior without memorizing every fact:
Atomic Radius
- Increases going DOWN a group (more electron shells)
- Decreases going RIGHT across a period (more protons pull electrons closer)
Ionization Energy
The energy required to remove an electron:
- Decreases going DOWN (electrons are farther from nucleus)
- Increases going RIGHT (electrons are held more tightly)
Electronegativity
The tendency to attract electrons in a bond:
- Decreases going DOWN
- Increases going RIGHT
- Fluorine is the most electronegative element (3.98)
Metallic Character
- Increases going DOWN and LEFT
- Metals are in the bottom-left; nonmetals in the top-right
The Block System
The periodic table is divided into blocks based on which subshell is being filled:
- s-block (Groups 1-2): Filling the s orbital
- p-block (Groups 13-18): Filling p orbitals
- d-block (Groups 3-12): Transition metals, filling d orbitals
- f-block (Lanthanides & Actinides): Filling f orbitals, shown below the main table
Special Element Categories
Metals (~75% of elements)
Good conductors, malleable, ductile, lustrous, tend to lose electrons.
Nonmetals
Poor conductors, brittle (when solid), tend to gain electrons. Located in the upper-right of the table.
Metalloids (Semimetals)
Along the staircase line (B, Si, Ge, As, Sb, Te). Properties between metals and nonmetals. Silicon is a semiconductor — the basis of modern computing!
Fun Facts
- Hydrogen is unique — it acts like both a metal and a nonmetal
- Oganesson (Og, 118) is the heaviest element ever created
- Technetium (Tc, 43) was the first artificially produced element
- Francium (Fr, 87) is the most unstable naturally occurring element
- The periodic table was first published by Dmitri Mendeleev in 1869
Explore the Table
Click any element to inspect properties, electron configuration, and more:
Explore every element interactively with our Periodic Table Tool — click any element to see its properties, electron configuration, and more.