Americium (Am): Bohr Model, Protons, Neutrons & Electrons
Americium is element number 95, an actinide in the f-block (the actinide row drawn below the table), period 7. Its atom has 95 protons, 148 neutrons and 95 electrons arranged in 7 shells: 2, 8, 18, 32, 25, 8, 2.
Protons, neutrons and electrons in americium
The atomic number of americium is 95, so every americium atom has 95 protons. A neutral atom has the same number of electrons, 95. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For americium-243, that is 243 − 95 = 148 neutrons. Every isotope of americium is radioactive; 243 is the mass number of its most stable one.
How to draw the Bohr model of americium
- Draw the nucleus and write 95 p⁺ and 148 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 32 electrons on it.
- Draw the fifth shell and put 25 electrons on it.
- Draw the sixth shell and put 8 electrons on it.
- Draw the seventh shell and put 2 electrons on it.
- Check: 2 + 8 + 18 + 32 + 25 + 8 + 2 = 95 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, 32, 25, 8, 2) is the one to draw.
Electron configuration
The electron configuration of americium is [Rn] 7s² 5f⁷. As an actinide it fills an inner f-subshell, and its common ion is Am³⁺.
Key facts about americium
| Symbol | Am |
|---|---|
| Atomic number | 95 |
| Relative atomic mass | [243] |
| Group · period · block | f-block · period 7 |
| Type | Actinide |
| State at 25 °C | solid |
| Electron shells | 2, 8, 18, 32, 25, 8, 2 |
| Electron configuration | [Rn] 7s² 5f⁷ |
| Valence electrons | varies (outer shell: 2) |
| Common ion | Am³⁺ |
| Electronegativity (Pauling) | 1.13 |
| First ionisation energy | 5.97 eV (576 kJ/mol) |
| Atomic radius (empirical) | 175 pm |
Where americium sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does americium have?
Americium has 95 protons and 95 electrons (atomic number 95). Its most common isotope, americium-243, has 243 − 95 = 148 neutrons.
What is the electron configuration of americium?
[Rn] 7s² 5f⁷. In shells that is 2, 8, 18, 32, 25, 8, 2.
How many valence electrons does americium have?
Americium is an actinide, so its valence electrons are spread over two shells; its outermost shell holds 2.
Where is americium on the periodic table?
In the f-block (the actinide row drawn below the table), period 7, in the f-block. It is an actinide.
