لانثانوم (La): Bohr Model, Protons, Neutrons & Electrons
لانثانوم is element number 57, a lanthanide in the f-block (the lanthanide row drawn below the table), period 6. Its atom has 57 protons, 82 neutrons and 57 electrons arranged in 6 shells: 2, 8, 18, 18, 9, 2.
Protons, neutrons and electrons in lanthanum
ال atomic number of lanthanum is 57, so every lanthanum atom has 57 protons. A neutral atom has the same number of electrons, 57. The number of neutrons depends on the isotope: neutrons = mass number − atomic number. For lanthanum-139, that is 139 − 57 = 82 neutrons. Lanthanum has 2 stable isotopes, with 81, 82 neutrons.
How to draw the Bohr model of lanthanum
- Draw the nucleus and write 57 p⁺ تم تصميم [الخدمة] لمتعلمين من جميع الأعمار، بما في ذلك طلاب المدارس. 82 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 9 electrons on it.
- Draw the sixth shell and put 2 electrons on it.
- Check: 2 + 8 + 18 + 18 + 9 + 2 = 57 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, 9, 2) is the one to draw.
Electron configuration
The electron configuration of lanthanum is [Xe] 6s² 5d¹. As a lanthanide it fills an inner f-subshell, and its common ion is La³⁺.
Key facts about lanthanum
| Symbol | La |
|---|---|
| Atomic number | 57 |
| Relative atomic mass | 138.91 |
| Group · period · block | f-block · period 6 |
| نوع | لانثانيد |
| State at 25 °C | solid |
| أغلفة الإلكترون | 2, 8, 18, 18, 9, 2 |
| Electron configuration | [Xe] 6s² 5d¹ |
| Valence electrons | varies (outer shell: 2) |
| Common ion | La³⁺ |
| Electronegativity (Pauling) | 1.10 |
| First ionisation energy | 5.58 eV (538 kJ/mol) |
| Atomic radius (empirical) | 195 pm |
Where lanthanum sits on the periodic table
الأسئلة الشائعة
How many protons, neutrons and electrons does lanthanum have?
Lanthanum has 57 protons and 57 electrons (atomic number 57). Its most common isotope, lanthanum-139, has 139 − 57 = 82 neutrons.
What is the electron configuration of lanthanum?
[Xe] 6s² 5d¹. In shells that is 2, 8, 18, 18, 9, 2.
How many valence electrons does lanthanum have?
Lanthanum is a lanthanide, so its valence electrons are spread over two shells; its outermost shell holds 2.
Where is lanthanum on the periodic table?
In the f-block (the lanthanide row drawn below the table), period 6, in the f-block. It is a lanthanide.
