Element 55 · Cesium (Cs)

Cesium Bohr model: diagram and electrons per shell

The cesium Bohr model shows a cesium atom (Cs) as a small nucleus with its electrons circling it in 6 shells: 2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N, 8 in shell O and 1 in shell P. This page has a rotating 3D cesium Bohr model, a flat diagram, a table of the electrons in each shell and the steps to draw it yourself.

Rotate the cesium Bohr model in 3D

Drag to orbit, scroll to zoom.

This is a Bohr model of cesium (Cs), a simplified picture of a single cesium atom. Its nucleus holds 55 protons, and a neutral cesium atom has 55 electrons, arranged around it in 6 shells (2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N, 8 in shell O and 1 in shell P).

Cs K · 21s² L · 82s² 2p⁶ M · 183s² 3p⁶ 3d¹⁰ N · 184s² 4p⁶ 4d¹⁰ O · 85s² 5p⁶ P · 16s¹

Cesium Bohr model diagram

Bohr model diagram of cesium: a nucleus of 55 protons with 55 electrons on 6 shells, 2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N, 8 in shell O and 1 in shell P, each ring labelled with its shell letter. — The cesium 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, 18 in shell N, 8 in shell O and 1 in shell P).

Cesium electrons per shell

A neutral cesium atom has 55 electrons, one for each of its 55 protons. They fill the shells from the nucleus outwards: 2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N, 8 in shell O and 1 in shell P.

Electrons in each shell of the cesium 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	18	32	4s² 4p⁶ 4d¹⁰
O	5	8	50	5s² 5p⁶
P	6	1	72	6s¹

How the cesium Bohr model builds up, shell by shell

Watch the cesium 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, 18 in shell N, 8 in shell O and 1 in shell P) as it forms.

Animation of the cesium Bohr model being built: a nucleus of 55 protons appears first, then each shell grows in around it and takes its electrons, giving 55 electrons on 6 shells (2 in shell K, 8 in shell L, 18 in shell M, 18 in shell N, 8 in shell O and 1 in shell P). — The cesium 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, 18 in shell N, 8 in shell O and 1 in shell P. Protons are red, neutrons yellow and electrons blue.

How to draw the cesium Bohr model

Find the atomic number. Cesium has atomic number 55, so a neutral atom has 55 protons and 55 electrons.
Draw the nucleus. Put a circle in the centre and write Cs in it. The 55 protons sit there with the neutrons.
Draw the shells. Sketch 6 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, 18 in shell N, 8 in shell O and 1 in shell P.
Check the total. 2 + 8 + 18 + 18 + 8 + 1 = 55, the atomic number, so every electron is accounted for.

Atomic data for the cesium Bohr model

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

Identity

Symbol: Cs
Atomic number: 55
Atomic mass: 132.9055 u
Family: Alkali Metals
Position: group 1, period 6
Block: s-block

Electron configuration

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s¹
Shorthand: [Xe] 6s¹
Electrons per shell: 2, 8, 18, 18, 8, 1
Outer-shell electrons: 1 in shell P

Ionisation energies

I₁: 375.7
I₂: 2234.3
I₃: 3400

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

Atomic radii

Calculated (pm): 298
Empirical (pm): 260
Covalent (pm): 232
Van der Waals (pm): 343

Electronegativity and electron affinity

Electronegativity (Pauling): 0.79
Electron affinity (kJ/mol): 45.505

Oxidation states

Charges the element commonly takes in compounds.

Physical properties, abundance and history of cesium

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

Physical properties

Phase at room conditions: Solid
Appearance: Silvery gold
Melting point: 28.55°C (301.7 K)
Boiling point: 670.85°C (944 K)
Density: 1.93 g/cm³
Thermal conductivity (W/m·K): 35.9
Specific heat (J/g·K): 0.242
Molar heat capacity (J/mol·K): 32.21
Heat of fusion (kJ/mol): 2.09
Heat of vaporisation (kJ/mol): 68.3

Abundance

Earth's crust (mg/kg): 3
Oceans (mg/L): 0

Discovery

Discovered by: Robert Bunsen
Year: 1860

Common compounds

Cesium Chloride ClCs
Cesium Cs
Cesium nitrate CsNO3
Cesium bromide BrCs
Cesium fluoride CsF
Cesium-137 Cs
Cesium iodide CsI
Cesium hydroxide CsHO

Compounds listed in the PubChem database.

Main isotopes of cesium

Isotopes of cesium share the same 55 protons but differ in neutrons. Natural isotopes come first, then the longest-lived others.

Main isotopes of cesium: mass number, abundance, half-life and decay
Mass number	Natural abundance	Half-life	Decay
131	–	9.689 d	EC
133	100 %	stable	–
134	–	2.065 y	β⁻, EC
135	–	1.33 My	β⁻
136	–	13.01 d	β⁻
137	–	30.04 y	β⁻

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

More about cesium

Cesium on the periodic table – properties, isotopes, uses and the full cesium page.
Alkali Metals – all alkali metal elements and their trends.
Bohr model of every element – the Bohr model of all 118 elements.