Lawrencium (Lr): Bohr Model, Protons, Neutrons & Electrons
Lawrencium is element number 103, an actinide in the f-block (the actinide row drawn below the table), period 7. Its atom has 103 protons, 163 neutrons and 103 electrons arranged in 7 shells: 2, 8, 18, 32, 32, 8, 3.
Protons, neutrons and electrons in lawrencium
The atomic number of lawrencium is 103, so every lawrencium atom has 103 protons. A neutral atom has the same number of electrons, 103. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For lawrencium-266, that is 266 − 103 = 163 neutrons. Every isotope of lawrencium is radioactive; 266 is the mass number of its most stable one.
How to draw the Bohr model of lawrencium
- Draw the nucleus and write 103 p⁺ and 163 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 32 electrons on it.
- Draw the sixth shell and put 8 electrons on it.
- Draw the seventh shell and put 3 electrons on it.
- Check: 2 + 8 + 18 + 32 + 32 + 8 + 3 = 103 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, 32, 8, 3) is the one to draw.
Electron configuration
The electron configuration of lawrencium is [Rn] 7s² 5f¹⁴ 7p¹. As an actinide it fills an inner f-subshell, and its common ion is variable.
Key facts about lawrencium
| Symbol | Lr |
|---|---|
| Atomic number | 103 |
| Relative atomic mass | [266] |
| Group · period · block | f-block · period 7 |
| Type | Actinide |
| State at 25 °C | unknown |
| Electron shells | 2, 8, 18, 32, 32, 8, 3 |
| Electron configuration | [Rn] 7s² 5f¹⁴ 7p¹ |
| Valence electrons | varies (outer shell: 3) |
| Common ion | — |
| Electronegativity (Pauling) | 1.30 |
| First ionisation energy | 4.96 eV (479 kJ/mol) |
| Atomic radius (empirical) | — |
Where lawrencium sits on the periodic table
Frequently asked questions
How many protons, neutrons and electrons does lawrencium have?
Lawrencium has 103 protons and 103 electrons (atomic number 103). Its most common isotope, lawrencium-266, has 266 − 103 = 163 neutrons.
What is the electron configuration of lawrencium?
[Rn] 7s² 5f¹⁴ 7p¹. In shells that is 2, 8, 18, 32, 32, 8, 3.
How many valence electrons does lawrencium have?
Lawrencium is an actinide, so its valence electrons are spread over two shells; its outermost shell holds 3.
Where is lawrencium 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.
