Radium (Ra)
Radium is element 88, an alkaline earth metal in group 2, period 7. A neutral atom has 88 protons, 138 neutrons and 88 electrons, 2 of them valence electrons.
Alkaline earth metal- Atomic number
- 88
- Atomic mass
- 226.03 u
- Valence electrons
- 2
- Protons · neutrons
- 88 · 138
- Electrons per shell
- 2, 8, 18, 32, 18, 8, 2
- At room temperature
- solid
Bohr model of radium
The Bohr model draws radium as a nucleus of 88 protons and 138 neutrons, with its 88 electrons on 7 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 32 in shell 4, 18 in shell 5, 8 in shell 6, 2 in shell 7. Press Build the atom to watch the shells fill from the inside out. The outer ring (the Q shell) is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of radium
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s²
Short form (noble gas notation): [Rn] 7s². The [Rn] stands for the electrons of radon, the noble gas before it.
How many valence electrons does radium have?
Radium has 2 valence electrons.
Radium is in group 2, so it has 2 valence electrons. It tends to lose them and form a +2 ion.
Protons, neutrons and electrons
| Protons | 88 | equal to the atomic number |
|---|---|---|
| Electrons | 88 | equal to the protons in a neutral atom |
| Neutrons | 138 | mass number 226 − 88 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Radium properties
| Symbol | Ra |
|---|---|
| Category | Alkaline earth metal |
| Group · period · block | 2 · 7 · s |
| Atomic mass | 226.03 u |
| State at 25 °C | solid |
| Melting point | 973 K (700 °C, 1,290 °F) |
| Boiling point | 1,413 K (1,140 °C, 2,080 °F) |
| Density | 5 g/cm³ |
| Electronegativity (Pauling) | 0.9 |
| Atomic radius | 283 pm |
| First ionization energy | 5.279 eV |
| Electron affinity | — |
| Oxidation states | +2 |
| Common ion charge | +2 |
| Discovered | 1898 by Pierre Curie |
Where radium sits on the periodic table
Group 2: Beryllium, Magnesium, Calcium, Strontium, Barium.
Questions about radium
How many valence electrons does radium have?
Radium has 2 valence electrons.
How many protons, neutrons and electrons does radium have?
A neutral radium atom has 88 protons and 88 electrons. Its most common form has about 138 neutrons (mass number 226 − 88 protons).
What is the electron configuration of radium?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s², written in short form as [Rn] 7s².
What does the Bohr model of radium look like?
A nucleus of 88 protons and 138 neutrons, circled by 7 electron shells holding 2, 8, 18, 32, 18, 8, 2 electrons.
What is the atomic number of radium?
88. The atomic number is the number of protons in the nucleus, and it is what makes an atom radium.