Krypton (Kr) – Periodic Table (Element Information & More)

This is a SUPER easy guide on Krypton element.

In fact, the table mentioned below is the perfect information box (Which gives you every single detail about the Krypton element in Periodic table.)

So if you want to know anything about Krypton element, then this guide is for you.

Let’s finish this very quickly.

Krypton Element (Kr) Information

Appearance	Colorless gas
State (at STP)	Gas
Position in Periodic table	Group: 18, Period: 4, Block: p
Category	Noble gases
Atomic number or  Protons	36
Neutrons	48
Electrons	36
Symbol	Kr
Atomic mass	83.798 u
Electrons arrangement or  Bohr model	2, 8, 18, 8
Electronic configuration	[Ar] 3d10 4s2 4p6
Atomic radius	202 picometers (van der Waals radius)
Valence electrons	8
1st Ionization energy	14.00 eV
Electronegativity	3.00 (Pauling scale)
Crystal structure	FCC (Face centered cubic)
Melting point	115.7 K or -157.3 °C or -251.2 °F
Boiling point	119.9 K or -153.4 °C or -244.1 °F
Density	3.75 g/L
Main isotope	84Kr
Who discovered Krypton and when?	William Ramsay and Morris Travers (in 1898)
CAS number	7439-90-9

Krypton in Periodic table

Krypton element is in group 18 and period 4 of the Periodic table. Krypton is the p-block element and it belongs to noble gases group.

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Why is Krypton in Group 18?

Do you know, how many electrons can be accommodated in the first shell, second shell, third shell, fourth shell, etc…?

Here is the table showing the capacity of orbits to hold electrons. 

Number of electrons in shells.

Orbit / Shell (n)	Maximum no. of electrons this orbit can hold
K shell, n = 1	2 × 1² = 2
L shell, n = 2	2 × 2² = 8
M shell, n = 3	2 × 3² = 18
N shell, n = 4	2 × 4² = 32

Thus, 

• 1st shell can hold 2 electrons.
• 2nd shell can hold 8 electrons.
• 3rd shell can hold 18 electrons.
• 4th shell can hold 32 electrons.

Now the atomic number of krypton (Kr) is 36.

Hence the krypton element has electrons arrangement 2, 8, 18, 8.

This electron arrangement indicates that the outermost orbit of Krypton element (Kr) has 8 electrons.

Hence, it lies in group 18.

Why is Krypton in Period 4?

Let me ask you a question.

How many shells does krypton have?

It’s 4. Right? 

You have already seen the bohr model of krypton atom in the above table.

From the Bohr model, it can be found that the number of orbits or shells in krypton is 4. Hence, as krypton has 4 orbits, it lies in period 4 of the Periodic table. 

Why is Krypton in p-block?

Before knowing this reason, first of all I want to ask you a simple question.

How can you determine the blocks-wise position of elements?

The simple answer: The elements will lie in the s, p, d or f block will completely depend upon the subshell in which the last electron will enter.

For example; the electron configuration of krypton is [Ar] 3d¹⁰ 4s² 4p⁶. 

So the last electron of krypton enters the p-subshell or p-orbital. 

Hence, krypton is the p-block element.

5 Interesting facts about Krypton

Interesting facts about krypton element are mentioned below.

1. The name krypton is derived from the Greek word “kryptos” meaning hidden.
2. Krypton is present in very less quantity in the earth’s atmosphere (around 1 ppm by volume).
3. The atmosphere of Mars contains only 0.3 ppm (by volume) of krypton gas.
4. When krypton gas is exposed to electric current under low pressure, it glows with a smoky white light.
5. Krypton is one of the products that is obtained from the fission of uranium.

Properties of Krypton

The physical and chemical properties of krypton element are mentioned below.

Physical properties of Krypton

Physical properties of krypton are mentioned below.

• Krypton is colorless, odourless and tasteless gas.
• The atomic mass of krypton is 83.798 u and its density is 3.75 g/L.
• The melting point of krypton is -157.3 °C and its boiling point is -153.4 °C.
• Krypton has various stable isotopes as well as synthetic isotopes. Out of these isotopes, ⁸⁴Kr is most abundant (around 57%).
• The van der Waals radius of the krypton atom is 202 picometers.
• The crystal structure of krypton element is FCC (face centered cubic).

Chemical properties of Krypton

Chemical properties of krypton are mentioned below.

• The electron shell configuration of krypton is 2, 8, 18, 8. This indicates that it has a completely filled outer shell, which makes it chemically stable.
• As krypton is chemically stable, it does not react with any other elements. And hence it does not have more chemical properties.
• It has been found that krypton reacts with fluorine to form krypton difluoride (KrF₂) under certain conditions.

Uses of Krypton

Uses of krypton are mentioned below.

• Krypton is used in incandescent lights to protect the filament from oxygen.
• As krypton is an inert gas, it is also used in double glazed windows in the space between the two panes, which provides thermal insulation. (but in most cases, argon is preferred for this application as argon is cheaper than krypton.)
• ⁸¹Kr is used to determine the age of ice present in Antarctica.
• As krypton produces a bright white light, it is used for flashes in photography.
• One of the isotopes of krypton also finds its applications in MRI technology.

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External resources:

1. Krypton – American Chemical Society. (2018, December 3). American Chemical Society. https://www.acs.org/molecule-of-the-week/archive/k/krypton.html
2. Krypton – Element information, properties and uses | Periodic Table. (n.d.). Krypton – Element Information, Properties and Uses | Periodic Table. https://www.rsc.org/periodic-table/element/36/krypton
3. Krypton – Wikipedia. (2016, June 23). Krypton – Wikipedia. https://en.wikipedia.org/wiki/Krypton
4. P. (n.d.). Krypton | Kr (Element) – PubChem. Krypton | Kr (Element) – PubChem. https://pubchem.ncbi.nlm.nih.gov/element/Krypton
5. It’s Elemental – The Element Krypton. (n.d.). It’s Elemental – the Element Krypton. https://education.jlab.org/itselemental/ele036.html