Element 89 · Actinium (Ac)

Actinium Bohr model: diagram and electrons per shell

The actinium Bohr model shows a actinium atom (Ac) 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, 18 in shell O, 9 in shell P and 2 in shell Q. This page has a rotating 3D actinium Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the actinium Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of actinium (Ac), a simplified picture of a single actinium atom. Its nucleus holds 89 protons, and a neutral actinium atom has 89 electrons, arranged around it in 7 shells (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O, 9 in shell P and 2 in shell Q).

Ac K · 21s² L · 82s² 2p⁶ M · 183s² 3p⁶ 3d¹⁰ N · 324s² 4p⁶ 4d¹⁰ 4f¹⁴ O · 185s² 5p⁶ 5d¹⁰ P · 96s² 6p⁶ 6d¹ Q · 27s²

Actinium Bohr model diagram

Bohr model diagram of actinium: a nucleus of 89 protons with 89 electrons on 7 shells, 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O, 9 in shell P and 2 in shell Q, each ring labelled with its shell letter. — The actinium 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, 18 in shell O, 9 in shell P and 2 in shell Q).

Actinium electrons per shell

A neutral actinium atom has 89 electrons, one for each of its 89 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, 18 in shell O, 9 in shell P and 2 in shell Q.

Electrons in each shell of the actinium Bohr model
Shell	Shell number (n)	Electrons	Most it can hold (2n²)	Subshells
K	1	2	2	1s²
L	2	8	8	2s² 2p⁶
M	3	18	18	3s² 3p⁶ 3d¹⁰
N	4	32	32	4s² 4p⁶ 4d¹⁰ 4f¹⁴
O	5	18	50	5s² 5p⁶ 5d¹⁰
P	6	9	72	6s² 6p⁶ 6d¹
Q	7	2	98	7s²

How the actinium Bohr model builds up, shell by shell

Watch the actinium 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, 18 in shell O, 9 in shell P and 2 in shell Q) as it forms.

Animation of the actinium Bohr model being built: a nucleus of 89 protons appears first, then each shell grows in around it and takes its electrons, giving 89 electrons on 7 shells (2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O, 9 in shell P and 2 in shell Q). — The actinium 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, 18 in shell O, 9 in shell P and 2 in shell Q. Protons are red, neutrons yellow and electrons blue.

How to draw the actinium Bohr model

Find the atomic number. Actinium has atomic number 89, so a neutral atom has 89 protons and 89 electrons.
Draw the nucleus. Put a circle in the centre and write Ac in it. The 89 protons sit there with the neutrons.
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.
Place the electrons. Fill from the inside out: 2 in shell K, 8 in shell L, 18 in shell M, 32 in shell N, 18 in shell O, 9 in shell P and 2 in shell Q.
Check the total. 2 + 8 + 18 + 32 + 18 + 9 + 2 = 89, the atomic number, so every electron is accounted for.

Atomic data for the actinium Bohr model

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

Identity

Symbol: Ac
Atomic number: 89
Atomic mass: [227] 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 6d¹
Shorthand: [Rn] 6d¹ 7s²
Electrons per shell: 2, 8, 18, 32, 18, 9, 2
Outer-shell electrons: 2 in shell Q

Ionisation energies

I₁: 499
I₂: 1170

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): 195
Covalent (pm): 186

Electronegativity and electron affinity

Electronegativity (Pauling): 1.1
Electron affinity (kJ/mol): 33.77

Oxidation states

Charges the element commonly takes in compounds.

Physical properties, abundance and history of actinium

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

Physical properties

Phase at room conditions: Solid
Melting point: 1226.85°C (1500 K)
Boiling point: 3226.85°C (3500 K)
Density: 10 g/cm³
Specific heat (J/g·K): 0.12
Molar heat capacity (J/mol·K): 27.2
Heat of fusion (kJ/mol): 10.5
Heat of vaporisation (kJ/mol): 292.9

Abundance

Earth's crust (mg/kg): 0

Discovery

Discovered by: Friedrich Oskar Giesel
Year: 1899

Common compounds

Actinium Ac
Actinium Ac-225 Ac
Actinium-227 Ac
Actinium(225Ac) Vipivotide Tetraxetan C49H68AcN9O16-3
Actinium-228 Ac
Actinium-224 Ac
Actinium-226 Ac
[[(5S)-3-[4-[3-[3,5-bis(trifluoromethyl)anilino]-2-hydroxy-propoxy]-3-fluoro-phenyl]-2-oxo-oxazolidin-5-yl]methylamino]actinium C21H19AcF7N3O4-

Compounds listed in the PubChem database.

Main isotopes of actinium

Isotopes of actinium share the same 89 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of actinium: mass number, abundance, half-life and decay
Mass number	Natural abundance	Half-life	Decay
224	–	2.78 h	β⁺, α, β⁻
225	–	9.919 d	α, 14C
226	–	29.37 h	β⁻, EC, α
227	–	21.772 y	β⁻, α
228	–	6.15 h	β⁻
229	–	62.7 min	β⁻

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

More about actinium

Actinium on the periodic table – properties, isotopes, uses and the full actinium page.
Actinides – all actinide elements and their trends.
Bohr model of every element – the Bohr model of all 118 elements.