What is the periodic table?
The periodic table organizes all 118 known chemical elements by their atomic number - the number of protons in the nucleus, which is what defines the element. Elements in the same column, called a group, tend to behave in similar ways chemically, while each row, called a period, corresponds to a new electron shell being filled. The colors here group elements into families: alkali metals, noble gases, halogens, transition metals and more.
How to read an element
Each tile shows the chemical symbol, the atomic number and the atomic mass. Opening an element reveals more: whether it is a solid, liquid or gas at room temperature, its melting and boiling points, how its electrons are arranged in shells, the year it was discovered, and a short fact about where you actually meet it in everyday life - from the lithium in your phone battery to the neon in a glowing sign.
Frequently asked questions
How many elements are in the periodic table?
There are 118 confirmed elements, from hydrogen (atomic number 1) to oganesson (118). The first 94 occur naturally on Earth; the rest have only been made in laboratories.
What does the atomic number mean?
The atomic number is the number of protons in an atom's nucleus, and it is what defines the element. Hydrogen always has 1 proton, carbon always has 6. In a neutral atom it also equals the number of electrons.
What is the difference between a group and a period?
Groups are the vertical columns: elements in the same group have similar chemical behaviour because they have the same number of outer electrons. Periods are the horizontal rows, and each one corresponds to filling a new electron shell.
Who created the periodic table?
Dmitri Mendeleev published the first widely recognized periodic table in 1869. He arranged the known elements by increasing atomic mass and left gaps for elements not yet discovered, correctly predicting several of their properties.