Barium (Ba)
Barium is element 56, an alkaline earth metal in group 2, period 6. A neutral atom has 56 protons, 81 neutrons and 56 electrons, 2 of them valence electrons.
Alkaline earth metal- Atomic number
- 56
- Atomic mass
- 137.33 u
- Valence electrons
- 2
- Protons · neutrons
- 56 · 81
- Electrons per shell
- 2, 8, 18, 18, 8, 2
- At room temperature
- solid
Bohr model of barium
The Bohr model draws barium as a nucleus of 56 protons and 81 neutrons, with its 56 electrons on 6 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 18 in shell 4, 8 in shell 5, 2 in shell 6. Press Build the atom to watch the shells fill from the inside out. The outer ring (the P 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 barium
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s²
Short form (noble gas notation): [Xe] 6s². The [Xe] stands for the electrons of xenon, the noble gas before it.
How many valence electrons does barium have?
Barium has 2 valence electrons.
Barium 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 | 56 | equal to the atomic number |
|---|---|---|
| Electrons | 56 | equal to the protons in a neutral atom |
| Neutrons | 81 | mass number 137 − 56 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.
Barium properties
| Symbol | Ba |
|---|---|
| Category | Alkaline earth metal |
| Group · period · block | 2 · 6 · s |
| Atomic mass | 137.33 u |
| State at 25 °C | solid |
| Melting point | 1,000 K (727 °C, 1,340 °F) |
| Boiling point | 2,170 K (1,900 °C, 3,450 °F) |
| Density | 3.62 g/cm³ |
| Electronegativity (Pauling) | 0.89 |
| Atomic radius | 268 pm |
| First ionization energy | 5.212 eV |
| Electron affinity | — |
| Oxidation states | +2 |
| Common ion charge | +2 |
| Discovered | 1808 by Carl Wilhelm Scheele |
Where barium sits on the periodic table
Group 2: Beryllium, Magnesium, Calcium, Strontium, Radium.
Questions about barium
How many valence electrons does barium have?
Barium has 2 valence electrons.
How many protons, neutrons and electrons does barium have?
A neutral barium atom has 56 protons and 56 electrons. Its most common form has about 81 neutrons (mass number 137 − 56 protons).
What is the electron configuration of barium?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s², written in short form as [Xe] 6s².
What does the Bohr model of barium look like?
A nucleus of 56 protons and 81 neutrons, circled by 6 electron shells holding 2, 8, 18, 18, 8, 2 electrons.
What is the atomic number of barium?
56. The atomic number is the number of protons in the nucleus, and it is what makes an atom barium.