What Is Radium?
Carrying the symbol Ra and atomic number 88, Radium is classified as an alkaline earth metal, one row down from the alkali metals.
A radioactive element discovered by Marie Curie. Was used in luminous watch dial paint.
As a alkaline earth metal in Period 7 and Group 2 (Alkaline Earth Metals), radium's placement on the table reflects its electron configuration of [Rn] 7s², which governs its bonding behavior and the type of compounds it typically forms.
Position on the Periodic Table
Radium is located in Period 7, the bottom row of the standard periodic table, consisting largely of radioactive and synthetic elements.
Within that row, radium sits in Group 2 (Alkaline Earth Metals), alongside elements that share a similar number of valence electrons and, by extension, similar chemical behavior.
This position is not arbitrary — the periodic table was deliberately organized so that an element's row and column reveal its expected reactivity, bonding pattern, and physical state at a glance.
Physical & Chemical Properties
Radium has an atomic mass of (226) u and a density of 5.5 g/cm³. Its melting point is 700°C and its boiling point is 1737°C.
Radium readily loses its two outer electrons to form a stable +2 ion, a pattern consistent across the whole alkaline earth group.
Electron Configuration Explained
Radium's electron configuration is [Rn] 7s², describing how its electrons are distributed across shells and subshells around the nucleus.
Reading the configuration in order shows electrons filling shells of increasing energy, following the standard Aufbau principle that explains how atomic structure builds up across the periodic table.
The outermost (valence) electrons shown in this configuration are what ultimately determine radium's chemical reactivity and the type of bonds it forms with other elements.
History & Discovery
Radium was formally discovered in 1898, Marie Curie, identified through the careful isolation and analytical techniques typical of that era's chemical research.
Many elements from this period were anticipated by Dmitri Mendeleev's periodic table, which successfully predicted gaps corresponding to undiscovered elements well before laboratory instruments existed to confirm them directly.
What Is Radium Used For?
Radium's specific properties make it useful in several applications, including:
- Historic cancer treatment
- Luminous paint (1910s–30s)
- Neutron sources
- Lightning rods
- Research
These uses reflect radium's underlying classification as a alkaline earth metal, since the same properties that define its category in chemistry also determine where it becomes practically useful.
Fun Facts About Radium
- The 'Radium Girls' — factory workers who painted watch dials in the 1920s — developed fatal radiation poisoning.
- Radium is element number 88 on the periodic table, in Period 7 and Group 2.
- Its standard atomic mass is (226) u, calculated from the natural abundance of its isotopes.
Frequently Asked Questions
What is Radium's atomic number?
Radium has atomic number 88.
What is Radium's chemical symbol?
Radium's symbol is Ra.
What group and period is Radium in?
Radium is in Period 7, Group 2 (Alkaline Earth Metals).
What is Radium's atomic mass?
Radium's standard atomic mass is (226) u.