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Cesium (Cs) – Element 55 of the periodic table

Cesium (symbol Cs) is element number 55 of the periodic table and belongs to the “Alkali metal” category. Its atomic mass is about 132.91, and its phase under standard conditions is Solid. This element sits in period 6 and group 1 of the periodic table, and its electrons are arranged in shells of 2, 8, 18, 18, 8, 1. The short electron configuration of Cesium is [Xe] 6s¹. Known uses of Cesium include Atomic clocks, Photoelectric cells and Oil drilling.

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Properties of Cesium

Atomic number
55
Chemical symbol
Cs
Atomic mass
132.91
Category
Alkali metal
Period
6
Group
1
Phase
Solid
Protons
55
Electrons
55
Neutrons (approx.)
78
Electron shells
2, 8, 18, 18, 8, 1
Outer-shell electrons
1
Discovered
Robert Bunsen (1860)

Electron configuration of Cesium

The electron configuration of Cesium (Cs), with 55 electrons, is shown below. The last shell (shell 6) is highlighted:

Full configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s¹
Short configuration
[Xe] 6s¹
Last shell
6s¹

What is electron configuration and how is it written?

Electron shells of Cesium

Distribution of 55 electrons of Cesium across shells K to P:

  1. K2
  2. L8
  3. M18
  4. N18
  5. O8
  6. P1

What is a alkali metal?

The alkali metals are the group 1 elements (excluding hydrogen): soft, shiny and highly reactive metals that react violently with water and are never found free in nature.

Uses of Cesium

Frequently asked questions about Cesium

What is the atomic number of Cesium?

The atomic number of Cesium (Cs) is 55; that is, every atom of it has 55 protons.

What is the electron configuration of Cesium?

The electron configuration of Cesium (Cs) is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s¹; in short form it is [Xe] 6s¹, and its last shell is 6s¹.

What is the chemical symbol of Cesium?

The chemical symbol of Cesium is Cs.

Where is Cesium located in the periodic table?

Cesium is located in period 6 and group 1 and belongs to the “Alkali metal” category.

What is the atomic mass of Cesium?

The atomic mass of Cesium is about 132.91 (atomic mass units).

What is the phase of Cesium under normal conditions?

The phase of Cesium under standard conditions is Solid.

What are the uses of Cesium?

Uses of Cesium include Atomic clocks, Photoelectric cells and Oil drilling.

Who discovered Cesium?

Cesium was discovered by Robert Bunsen in 1860.

Elements in the same category as Cesium (Alkali metal)

Lithium (Li)Sodium (Na)Potassium (K)Rubidium (Rb)Francium (Fr)

See all Alkali metals

Cesium’s group 1 neighbours

Hydrogen (H)Lithium (Li)Sodium (Na)Potassium (K)Rubidium (Rb)Francium (Fr)

Group 1 of the periodic table