88 Ra

Radium (Ra)

Element 88 · Alkaline earth metal · Solid at 25 °C · Group 2, Period 7

Radium, discovered by the Curies, once glowed on watch dials and was sold in quack cures before its dangers were understood; its handling helped create radiation safety science.

On the periodic table, radium sits in group 2 — the alkaline earth metals — in period 7. It is one of 6 elements classified as an alkaline earth metal, and at room temperature (25 °C) it is a solid.

The alkaline earth metals carry two outer electrons and form 2+ ions in almost all of their chemistry. They are harder, denser, and less violently reactive than their alkali-metal neighbors in group 1, but still too reactive to occur uncombined in nature. Their compounds are everywhere — in limestone, bones, fireworks, and lightweight alloys.

Properties of radium

Properties of Radium
Atomic number (Z)	88
Symbol	Ra
Atomic mass	(226) (mass number of the most stable isotope; this element has no standard atomic weight)
Category	Alkaline earth metal
Group	2
Period	7
Block	s-block
Metal / nonmetal	Metal
State at 25 °C	Solid
Electron configuration	[Rn] 7s2
Electronegativity (Pauling)	0.9
Melting point	700 °C (973.15 K / 1,292 °F)
Boiling point	1,737 °C (2,010.15 K / 3,158.6 °F)
Density	5.5 g/cm³

Position in the periodic table

Radium shares group 2 — the alkaline earth metals with Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba). Elements in the same group have the same number of outer electrons, so they tend to behave alike chemically — comparing them is one of the fastest ways to see periodic trends in action.

Physical properties

Radium melts at 700 °C (973.15 K / 1,292 °F) and boils at 1,737 °C (2,010.15 K / 3,158.6 °F), giving it a liquid range of about 1,037 °C at standard pressure.

Its density is 5.5 g/cm³.

Data notes

The atomic mass is shown in parentheses because this element has no standard atomic weight; the number given is the mass number of its most stable known isotope.