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Chromium [Cr] – Element Details, History, Atomic Structure, Facts, Properties, Electronic Configuration, Atomic Spectrum, Uses.

Chromium

Element 24 of Periodic table is Chromium with atomic number 24, atomic weight 51.9961. Chromium, symbol Cr, has a Body Centered Cubic structure and Silver color. Chromium is a Transition Metal element. It is part of group 6 (chromium family). Know everything about Chromium Facts, Physical Properties, Chemical Properties, Electronic configuration, Atomic and Crystal Structure.

History of Chromium

The element Chromium was discovered by N. Vauquelin in year 1797 in France. Chromium was first isolated by N. Vauquelin in 1798. Chromium derived its name from the Greek word chroma, meaning ‘color’.

Vauquelin discovered the trioxide incrocoiteore, and later isolated the metal by heating the oxide in a charcoal oven.

How to Locate Chromium on Periodic Table

Periodic table is arranged by atomic number, number of protons in the nucleus which is same as number of electrons. The atomic number increases from left to right. Periodic table starts at top left ( Atomic number 1) and ends at bottom right (atomic number 118). Therefore you can directly look for atomic number 24 to find Chromium on periodic table.

Another way to read periodic table and locate an element is by using group number (column) and period number (row). To locate Chromium on periodic table look for cross section of group 6 and period 4 in the modern periodic table.

Chromium Facts

Name
Chromium
Atomic Symbol
Cr
Atomic Number
24
Phase
Solid
Atomic Weight
51.9961
Colour
Silver
Classification
Transition Metal
Group in Periodic Table
6
Group Name
Chromium family
Block in Periodic Table
d-block
Period in Periodic Table
4
Electronic Configuration
[Ar] 3d5 4s1
Melting Point
2180 K
Boiling Point
2944 K
Electronic Shell Structure
2, 8, 13, 1
CAS Number
CAS7440-47-3

Chromium Atomic Structure and Orbital Properties

Chromium atoms have 24 electrons and the electronic shell structure is [2, 8, 13, 1] with Atomic Term Symbol (Quantum Numbers) 7S3.

Element Properties

Atomic Number
24
Number of Protons
24
Mass Number
52
Number of Neutrons
28
Shell structure (Electrons per energy level)
2, 8, 13, 1
Electron Configuration
[Ar] 3d5 4s1
Valence Electrons
3d5 4s1
Oxidation State
-4, -2, -1, 0, 1, 2, 3, 4, 5, 6
Atomic Term Symbol (Quantum Numbers)
7S3

Atomic Structure of Chromium

Atomic Radius
166 pm (1.66 Å)
Atomic Radius Empirical
140 pm (1.4 Å)
Atomic Volume
7.2824 cm3/mol
Covalent Radius
127 pm (1.27 Å)
Van der Waals Radius
188 pm
Neutron Cross Section
3.1
Neutron Mass Absorption
0.0021

Crystal Structure of Chromium

The solid state structure of Argon is Face Centered Cubic.

The Crystal structure can be described in terms of its unit Cell. The unit Cells repeats itself in three dimensional space to form the structure.

The unit cell is represented in terms of its lattice parameters, which are the lengths of the cell edges Lattice Constants (a[291 pm]b[291 pm] and c[291 pm]) and the angles between them Lattice Angles (alpha[π/2], beta[π/2] and gamma[π/2])

The positions of the atoms inside the unit cell are described by the set of atomic positions ( xi, yi, zi) measured from a reference lattice point.

The symmetry properties of the crystal are described by the concept of space groups. All possible symmetric arrangements of particles in three-dimensional space are described by the 230 space groups (219 distinct types, or 230 if chiral copies are considered distinct.

Space Group Name

Space Group Number

Crystal Structure

Number of atoms per unit cell

Im_ 3m

229

Body Centered Cubic

2

Ground State Electronic Configuration of Chromium- neutral Argon Chromium

Abbreviated electronic configuration of Chromium

The ground state abbreviated electronic configuration of Neutral Chromium atom is [Ar] 3d5 4s1. The portion of Chromium configuration that is equivalent to the noble gas of the preceding period, is abbreviated as [Ar]. For atoms with many electrons, this notation can become lengthy and so an abbreviated notation is used. This is important as it is the Valence electrons 3d5 4s1, electrons in the outermost shell that determine the chemical properties of the element.

Unabbreviated electronic configuration of neutral Chromium

Complete ground state electronic configuration for the Chromium atom, Unabbreviated electronic configuration

1s2 2s2 2p6 3s2 3p6 3d5 4s1

Electrons are filled in atomic orbitals as per the order determined by the Aufbau principle, Pauli Exclusion Principle and Hund’s Rule.

  • As per the Aufbau principle the electrons will occupy the orbitals having lower energies before occupying higher energy orbitals. According to this principle, electrons are filled in the following order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p…
  • The Pauli exclusion principle states that a maximum of two electrons, each having opposite spins, can fit in an orbital.
  • Hund’s rule states that every orbital in a given subshell is singly occupied by electrons before a second electron is filled in an orbital.

Regulatory and Health - Health and Safety Parameters and Guidelines

CAS Number
RTECS Number
EU Number
DOT Hazard Class
4.1
DOT Numbers
3089
NFPA Fire Rating
1
NFPA Hazards
Autoignition Point
400 °C
NFPA Health Rating
2
NFPA Reactivity Rating
1
Flashpoint

Chromium Chemical Properties : Argon Ionization Energies and electron affinity

ElectronAffinity
64.3 kJ/mol
Valence
6
Electronegativity
1.66

Chromium Physical & Elastic Properties

Density
7.14 g/cm3(when liquid at m.p density is $6.3 g/cm3)
Molar Volume
7.2824 cm3/mol
Young Modulus
279
Shear Modulus
115 GPa
Bulk Modulus
160 GPa
Poisson Ratio
0.21

Chromium Electrical Properties

Electrical Conductivity
7900000 S/m
Resistivity
1.3e-7 m Ω
Superconducting Point

Chromium Magnetic Properties

Magnetic Type
Antiferromagnetic
Curie Point
N/A
Mass Magnetic Susceptibility
4.45e-8 m3/kg
Molar Magnetic Susceptibility
2.314e-9 m3/mol
Volume Magnetic Susceptibility
0.0003177

Chromium Thermal Properties

Melting Point
2180 K (1906.85°C, 3464.3299999999995 °F)
Boiling Point
2944 K (2670.85°C, 4839.53 °F)
Critical Temperature
N/A
Superconducting Point
N/A

Use of Chromium

Chromium is used to produce seversl alloys. It is used to harden steel and manufacture stainless steel. Chromium plating can be used to give a polished mirror finish to steel. Chromium-plated car and lorry parts, such as bumpers, were once very common.

106. Seaborgium [Sg]