Radium (Ra) VS Actinium (Ac)
A definitive side-by-side comparison of two essential element profiles.
VS
Main Differences
Radium (Ra) is an element in the alkaline earth metals category with an atomic number of 88. Actinium (Ac) is an element in the actinoids category with an atomic number of 89.
Actinium (Ac) is 1.8x denser than Radium (Ra). However, Actinium (Ac) melts at a higher temperature than Radium (Ra) (a difference of 350.0 Kelvin).
Where do the names come from?
Ra Radium (Ra) Naming History
The name Radium is derived from the Latin ''radius'', meaning ray.
Ac Actinium (Ac) Naming History
The name Actinium is derived from the Greek ''actinos'', meaning a ray.
Related Comparisons
Compare
Radium (Ra)
Actinium (Ac)
Category
Alkaline Earth Metals
Actinoids
Atomic Number
88
89
Symbol
Ra
Ac
Atomic Mass
[226] u
[227] u
Group
2
Actinides
Period
7
7
Block
s-block
d-block
Standard State (at 20°C)
solid
solid
Density
5.5 g/cm³
10.07 g/cm³
Melting Point (°C)
696°C
1050°C
Melting Point (°F)
1285°F
1922°F
Melting Point (K)
973 K
1323 K
Boiling Point (°C)
1500°C
3200°C
Boiling Point (°F)
2732°F
5792°F
Boiling Point (K)
2010 K
3471 K
Year Discovered:
1898
1899
CAS Number
7440-14-4
7440-34-8
Origin of Name:
The name is derived from the Latin ''radius'', meaning ray.
The name is derived from the Greek ''actinos'', meaning a ray.