Antimony (Sb): Bohr Model, Protons, Neutrons & Electrons
Antimony is element number 51, a metalloid in group 15, period 5. Its atom has 51 protons, 70 neutrons and 51 electrons arranged in 5 shells: 2, 8, 18, 18, 5.
Protons, neutrons and electrons in antimony
The atomic number of antimony is 51, so every antimony atom has 51 protons. A neutral atom has the same number of electrons, 51. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For antimony-121, that is 121 − 51 = 70 neutrons. Antimony has 2 stable isotopes, with 70, 72 neutrons.
How to draw the Bohr model of antimony
- Draw the nucleus and write 51 p⁺ and 70 n⁰ inside it.
- Draw the first shell and put 2 electrons on it (the first shell holds at most 2).
- Draw the second shell and put 8 electrons on it.
- Draw the third shell and put 18 electrons on it.
- Draw the fourth shell and put 18 electrons on it.
- Draw the fifth shell and put 5 electrons on it.
- Check: 2 + 8 + 18 + 18 + 5 = 51 electrons, the same as the number of protons.
From potassium onwards the shells don’t simply fill as 2, 8, 8: the fourth shell starts before the third is full, so the real arrangement above (2, 8, 18, 18, 5) is the one to draw.
Electron configuration
The electron configuration of antimony is [Kr] 5s² 4d¹⁰ 5p³. Its 5 outer electrons decide how it reacts: it tends to lose them, forming Sb³⁺ ions.
Key facts about antimony
| Symbol | Sb |
|---|---|
| Atomic number | 51 |
| Relative atomic mass | 121.76 |
| Group · period · block | group 15 · period 5 · p-block |
| Type | Metalloid |
| State at 25 °C | solid |
| Electron shells | 2, 8, 18, 18, 5 |
| Electron configuration | [Kr] 5s² 4d¹⁰ 5p³ |
| Valence electrons | 5 |
| Common ion | Sb³⁺ |
| Electronegativity (Pauling) | 2.05 |
| First ionisation energy | 8.61 eV (831 kJ/mol) |
| Atomic radius (empirical) | 145 pm |
Where antimony sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does antimony have?
Antimony has 51 protons and 51 electrons (atomic number 51). Its most common isotope, antimony-121, has 121 − 51 = 70 neutrons.
What is the electron configuration of antimony?
[Kr] 5s² 4d¹⁰ 5p³. In shells that is 2, 8, 18, 18, 5.
How many valence electrons does antimony have?
5. Antimony is in group 15, and its outer shell holds 5 electrons.
Where is antimony on the periodic table?
In group 15, period 5, in the p-block. It is a metalloid.
