Science

Periodic Table

Interactive chemistry reference

Element Categories

alkali
alkaline
transition
post transition
metalloid
nonmetal
halogen
noble gas

About Periodic Table

Browse every element and open any one for its symbol, atomic number, mass, and group. A quick reference for chemistry homework and revision.

The table's layout is the information. Elements are arranged by atomic number, and the columns group elements with similar behaviour, which is why position tells you so much about how something reacts.

How to use it

  1. 1Browse the table or search for an element.
  2. 2Open an element to see its properties.
  3. 3Use its group and period position to reason about how it behaves.

Reading the table

  • Atomic number is the count of protons and defines the element. Atomic mass is roughly protons plus neutrons and varies between isotopes.
  • Columns are groups, and elements within one share outer-electron structure, which is why they behave similarly. Group 1 metals are all highly reactive; group 18 noble gases are all largely inert.
  • Rows are periods, and moving across one adds electrons to the same shell, which is why properties shift gradually from metallic to non-metallic.
  • Reactivity increases down group 1 and up group 17, which is why caesium reacts violently with water and fluorine is the most reactive non-metal.
  • The staircase between metals and non-metals marks the metalloids, which show properties of both and underpin semiconductor technology.

Frequently asked questions

What is the difference between atomic number and atomic mass?

Atomic number counts protons and determines which element it is. Atomic mass is approximately protons plus neutrons, and differs between isotopes of the same element.

Why are elements in the same column similar?

Because they share the same outer-electron arrangement, and chemical behaviour is governed almost entirely by outer electrons. This is the insight that makes the table predictive rather than merely a list.

What are the noble gases?

Group 18, on the far right. Their outer electron shells are full, so they have very little tendency to react, which is why they were the last major group to be discovered.