Modern periodic law and naming new elements

In 1913, Moseley studied the X-rays given out by different elements and showed that the atomic number, not the atomic mass, is the more fundamental property of an element. So the periodic law was restated.

Modern periodic law: the physical and chemical properties of the elements are periodic functions of their atomic numbers.

The long form of the periodic table, used today, has:

• 7 periods (horizontal rows). They hold 2, 8, 8, 18, 18, 32 and 32 elements.
• 18 groups (vertical columns), numbered 1 to 18 as recommended by IUPAC.
• Two rows, the lanthanoids and the actinoids, placed in separate panels below the main table to keep it from becoming too wide.

Elements in the same group have similar properties; they are often given family names: group 1 the alkali metals, group 2 the alkaline earth metals, group 17 the halogens, group 18 the noble gases.

When a new, very heavy element is made, scientists may argue about who discovered it first and what to call it. So until it is confirmed and officially named, IUPAC gives it a temporary systematic name, built from roots for each digit of its atomic number, followed by '-ium':

For example, element 120 would be un-bi-nil-ium, unbinilium, with the symbol Ubn (the first letters of the roots). Elements 101 to 118 now all have official names, from mendelevium (Md) to oganesson (Og), many of them honouring scientists or places.