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Element 91 · Protactinium (Pa)

Protactinium Bohr model: diagram and electrons per shell

The protactinium Bohr model shows a protactinium atom (Pa) as a small nucleus with its electrons circling it in 7 shells: 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 20 in shell O, 9 in shell P and 2 in shell Q. This page has a rotating 3D protactinium Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the protactinium Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of protactinium (Pa), a simplified picture of a single protactinium atom. Its nucleus holds 91 protons, and a neutral protactinium atom has 91 electrons, arranged around it in 7 shells (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 20 in shell O, 9 in shell P and 2 in shell Q).

Pa K · 21s2 L · 82s2 2p6 M · 183s2 3p6 3d10 N · 324s2 4p6 4d10 4f14 O · 205s2 5p6 5d10 5f2 P · 96s2 6p6 6d1 Q · 27s2

Protactinium Bohr model diagram

Bohr model diagram of protactinium: a nucleus of 91 protons with 91 electrons on 7 shells, 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 20 in shell O, 9 in shell P and 2 in shell Q, each ring labelled with its shell letter.
The protactinium Bohr model drawn flat: each ring is a shell, labelled with its letter, and every dot is an electron (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 20 in shell O, 9 in shell P and 2 in shell Q).

Protactinium electrons per shell

A neutral protactinium atom has 91 electrons, one for each of its 91 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 20 in shell O, 9 in shell P and 2 in shell Q.

Electrons in each shell of the protactinium Bohr model
ShellShell number (n)ElectronsMost it can hold (2n²)Subshells
K1221s2
L2882s2 2p6
M318183s2 3p6 3d10
N432324s2 4p6 4d10 4f14
O520505s2 5p6 5d10 5f2
P69726s2 6p6 6d1
Q72987s2

How the protactinium Bohr model builds up, shell by shell

Watch the protactinium Bohr model come together: the nucleus first, then each shell in turn, from the innermost outwards, with its electrons joining the ring. The legend names every shell and counts its electrons, so you can read off the arrangement (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 20 in shell O, 9 in shell P and 2 in shell Q) as it forms.

Animation of the protactinium Bohr model being built: a nucleus of 91 protons appears first, then each shell grows in around it and takes its electrons, giving 91 electrons on 7 shells (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 20 in shell O, 9 in shell P and 2 in shell Q).
The protactinium Bohr model built up in six seconds: the nucleus first, then each shell with its electrons, ending with 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 20 in shell O, 9 in shell P and 2 in shell Q. Protons are red, neutrons yellow and electrons blue.

How to draw the protactinium Bohr model

  1. Find the atomic number. Protactinium has atomic number 91, so a neutral atom has 91 protons and 91 electrons.
  2. Draw the nucleus. Put a circle in the centre and write Pa in it. The 91 protons sit there with the neutrons.
  3. Draw the shells. Sketch 7 shells as rings around the nucleus. A shell holds at most 2n² electrons: 2 in the first, 8 in the second, 18 in the third and 32 in the fourth.
  4. Place the electrons. Fill from the inside out: 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 20 in shell O, 9 in shell P and 2 in shell Q.
  5. Check the total. 2 + 8 + 18 + 32 + 20 + 9 + 2 = 91, the atomic number, so every electron is accounted for.

Atomic data for the protactinium Bohr model

The numbers behind the protactinium Bohr model, grouped by topic. Radii are in picometres (pm) and energies in kilojoules per mole (kJ/mol).

Identity

Symbol
Pa
Atomic number
91
Atomic mass
231.0359 u
Family
Actinides
Position
period 7 of the f-block
Block
f-block

Electron configuration

Full
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f2 6d1
Shorthand
[Rn] 5f2 6d1 7s2
Electrons per shell
2, 8, 18, 32, 20, 9, 2
Outer-shell electrons
2 in shell Q

Ionisation energies

I₁
568

Energy to remove each electron in turn (kJ/mol). A sharp jump means the next electron comes from an inner shell.

Atomic radii

Empirical (pm)
180
Covalent (pm)
169

Electronegativity and electron affinity

Electronegativity (Pauling)
1.5
Electron affinity (kJ/mol)
53.03

Oxidation states

+5

Charges the element commonly takes in compounds.

Physical properties, abundance and history of protactinium

Bulk properties of protactinium, how common it is, who discovered it and some of its compounds.

Physical properties

Phase at room conditions
Solid
Appearance
Bright, silvery metallic luster
Melting point
1567.85°C (1841 K)
Boiling point
4026.85°C (4300 K)
Density
15.37 g/cm³
Heat of fusion (kJ/mol)
16.7
Heat of vaporisation (kJ/mol)
481.2

Abundance

Earth's crust (mg/kg)
0
Oceans (mg/L)
0

Discovery

Discovered by
William Crookes
Year
1913
Named by
Otto Hahn

Common compounds

  • Protactinium Pa
  • Protactinium-231 Pa
  • Protactinium-230 Pa
  • Protactinium(4+) diethanedioate C4O8Pa-4
  • Protactinium-234 Pa
  • Protactinium-233 Pa
  • Protactinium, isotope of mass 232 Pa
  • Protactinium-228 Pa

Compounds listed in the PubChem database.

Main isotopes of protactinium

Isotopes of protactinium share the same 91 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of protactinium: mass number, abundance, half-life and decay
Mass numberNatural abundanceHalf-lifeDecay
228–22 hβ⁺, α
229–1.55 dEC, α
230–17.4 dβ⁺, β⁻, α
231100 %32.65 kyα, SF, 24Ne, 23F
232–1.32 dβ⁻, EC
233–26.975 dβ⁻

α = alpha decay, β⁻ = beta-minus, β⁺ = beta-plus, EC = electron capture, SF = spontaneous fission, p / n = proton / neutron emission.

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