How to read the periodic table
Each box shows an element's atomic number at the top and its chemical symbol in the middle. The atomic number is the number of protons in the nucleus and fixes which element it is. Elements run left to right in order of atomic number, and a new row, or period, starts when a new electron shell begins to fill, so there are seven periods. The 18 columns are the groups: group 1 holds the alkali metals such as sodium and potassium, group 17 the halogens such as chlorine, and group 18 the noble gases such as neon and argon. The two rows printed underneath are the lanthanides and actinides, drawn apart only to keep the table narrow.
Standard atomic weights and their uncertainty
The atomic weight of an element in a normal sample is an average over its isotopes. The values here are the abridged standard atomic weights published by CIAAW, the IUPAC commission responsible for them, in its 2024 table, which is based on the Atomic Weights 2021 report with later revisions for gadolinium, lutetium and zirconium. The ± figure shows how much the value can vary: lithium is 6.94 ± 0.06 because the mix of its isotopes differs from one natural source to another. Thirty-four elements, such as technetium, radon and everything from neptunium onwards, have no stable isotopes, so CIAAW gives them no standard atomic weight, and this table leaves the value blank instead of printing a guess.
Element categories
The colours group elements by behaviour: alkali and alkaline earth metals, transition and post-transition metals, metalloids, nonmetals, halogens, noble gases, lanthanides and actinides. Category boundaries are partly a matter of convention; this table follows the classification in the PubChem periodic table dataset from the US National Library of Medicine, which also provides the electron configurations, states and discovery years. For the heaviest elements, which have only ever been made a few atoms at a time, the state at room temperature is shown as not known.
Element names in Arabic
Arabic names follow the forms used in Arabic school chemistry books. Most are transliterations of the international names, such as هيدروجين for hydrogen and صوديوم for sodium, while metals known since ancient times keep their Arabic words: ذهب for gold, فضة for silver, حديد for iron, نحاس for copper and رصاص for lead. Some names have more than one accepted spelling, for example زنك and خارصين for zinc. The search accepts Arabic with or without hamza, so you can type اكسجين or أكسجين.