Interactive Periodic Table

How to use Interactive Periodic Table

1. Select an element to see its properties.
2. Note its group and period — the position predicts much of its behaviour.
3. Compare down a group to see the trends.
4. Atomic mass is a weighted average across naturally occurring isotopes, not a single atom.
5. Group number indicates outer electron configuration, which is what drives reactivity.
6. Elements beyond 92 are synthetic and most are intensely short-lived.

The layout is the information

Elements are ordered by atomic number — protons in the nucleus — and wrapped into rows so that elements with the same outer electron configuration line up in columns. That is why a group behaves alike: the alkali metals in group 1 all have a single outer electron they shed easily, and the noble gases in group 18 have a full shell and react with almost nothing. Mendeleev built this in 1869 from properties alone, before anyone knew about protons, and left gaps for elements he predicted — gallium and germanium arrived within fifteen years and matched his predictions closely.

The trends worth carrying in your head

Atomic radius decreases across a period and increases down a group, because added protons pull the same shell tighter while new shells sit further out. Electronegativity runs the opposite way, peaking at fluorine. Ionisation energy broadly rises across a period. Metals sit left, non-metals right, with the metalloids on the staircase between — which is where the semiconductors live, and why silicon and germanium matter so much.

Atomic mass is an average, which is why it is not a whole number

Chlorine’s 35.45 is not a chlorine atom; it is the weighted average of chlorine-35 and chlorine-37 as they occur naturally. Individual atoms have whole-number nucleon counts, and the mass on the table reflects natural isotopic abundance — which is why it differs slightly depending on where a sample was mined, and why IUPAC now gives ranges rather than single values for several elements.

The far end of the table

Everything past uranium is synthetic, made atom by atom in accelerators, and most exists for milliseconds. Oganesson, element 118, has been produced in quantities of a few atoms total. The seventh row was completed in 2016, and whether an eighth exists is an open question — there may be an ‘island of stability’ near element 126 where nuclei last longer, which is a genuine prediction nobody has yet been able to test.