Chromium is one of those unique elements that can exhibit more than one charge. The charge this transition metal exhibits depends on how it reacts with another element.
An element forms a charge when it loses or gains electrons. It forms a cation when it loses electrons and forms an anion when it gains an electron. Chromium is a metal; therefore, it is more likely to lose an electron to form a cation.
As mentioned earlier, chromium tends to lose different numbers of electrons in different reactions. So, can chromium have a definite charge? Continue reading to find out.
Properties of chromium
- Chromium is the fourth transition metal on the periodic table
- It has an atomic number of 24, a mass number of 52, and an electronic configuration of 1s22s22p63s23p63d54s1
- Chromium is a lustrous silvery solid at room temperature. It has a boiling point of 4,840°F (2,671°C) and a melting point of 3,465°F (1,907°C)
- At its melting point, chromium has a density of 6.3 g/cm3. When it’s a solid, its density is higher (7.15 g/cm3)
- Chromium is relatively abundant in the Earth’s crust but it is not found in its pure form. Chromium is found in the chromite ore (FeCr2O4) and its pure form is gotten through the roasting and leaching of chromite to remove iron
- Chromium finds applications across various industries because of its high resistance to corrosion and tarnishing
- Most of the chromium found in the Earth is used in the production of metal alloys. Other applications of chromium are seen in the production of stainless steel, chromate pigments, wood preservation, and hydrocarbon catalysis
- Additionally, impure chromium like chromite and chromium(III) oxides are used in blast furnaces, as foundry sand in metal casting, in cement kilns, and in molds for firing bricks
What is the charge of chromium?
Chromium can exhibit +1, +2, +3, +4, +5, and +6 charges, a characteristic property of transition metals.
However, +2, +3, and +6 charges are the most common and stable. As a metal, chromium will naturally lose electrons to form a cation. The number of electrons it loses to form a compound determines its charge.
What is the charge of Cr in dichromate ions?
You can determine the charge of Cr in the dichromate ion, Cr2O72−, by substituting the oxidation number of all elements in the compound.
2Cr + 7(-2) = -2
2Cr – 14 = -2
Cr = (-2 +14)/2
Cr = +6
What is the charge of chromium in chromic acid?
The charge of Cr in chromic acid, H2CrO4, can be determined as follows using the oxidation numbers of all other elements in the chemical formula.
2(1) + Cr + 4(-2) = 0
2 + Cr – 8 = 0
Cr = +6
What is the nuclear charge of chromium?
The nuclear charge of chromium is 24. This is the total charge of the protons in the nucleus of the chromium atom.
What is the Zeff of chromium?
The Zeff of chromium can be determined using Slater’s rule. Zeff is determined by the formula,
Zeff = Z – S, where Z is the nuclear charge and S is the shielding constant.
The first step is to write out the electronic configuration of chromium: 1s22s22p63s23p63d54s1.
Using Slater’s rule, determine the shielding constant by assigning values to electrons in each orbital. Electrons in 1s22s22p6 (10) have a shielding effect of 1, electrons in 3s23p63d5 (13) have a shielding effect of 0.85, and the electron (0) in 4s1 has a shielding effect of 0.35.
S = (0 x 0.35) + (13 x 0.85) + (10 x 1)
= 0 + 11.05 + 10
= 21.05
Z = 24, S = 21.05
Zeff = 24 – 21.05
Zeff = 2.95
What are the reactions of chromium?
Chromium does not readily react with water and oxygen at room temperature. But it reacts with other elements and compounds.
Reaction with the halogens
Chromium reacts with members of the halogen family under very mild conditions. It reacts with each halogen to form corresponding colored trihalides.
- 2Cr (s) + 3F2 (g) ———> 2CrF3 (s) (green)
- 2Cr (s) + 3Cl2 (g) ———> 2CrCl3 (s) (red-violet)
- 2Cr (s) + 3Br2 (g) ———> 2CrBr3 (s) (very dark green)
- 2Cr (s) + 3I2 (g) ———> 2CrI3 (s) (very dark green)
Reaction with aqueous ammonia
Cr(III) is precipitated by NH3 as Cr(OH)3. The chromium ions dissolve in excess ammonia.
[Cr(H2O)6]3+(aq) + 3NH3 (aq) ———> [Cr(OH)3(H2O)3] (s) + 3NH4+(aq)
[Cr(OH)3(H2O)3] (s) + 6NH3 (aq) ———> [Cr(NH3)6]3+(aq) + 3H2O(l) + 3OH−(aq)
Reaction with acids
Solid chromium reacts with hydrochloric acid and sulphuric acid to form a solution of Cr2+ and H2. But it does not react with HNO3. In aqueous solution, chromium(II) ions are present as a complex ion, [Cr(OH2)6]2+.
Cr (s) + 2HCl (aq) ———> Cr2+(aq) + 2Cl−(aq) + H2 (g)
Reaction with carbonate
Carbonate precipitates Cr3+ as Cr(OH)3. In excess carbonate, the precipitate is insoluble.
2[Cr(H2O)6]3+(aq) + 3CO32−(aq) ———> 2[Cr(OH)3(H2O)3] (s) + 3H2O (l) + 3CO2 (g)
Reaction with peroxide
Hydrogen peroxide oxidizes Cr(III) to chromate anion, CrO42−. The reaction is as follows:
2Cr(OH)4 (aq) + 3H2O2 (aq) + 2OH−(aq) ———> 2CrO42−(aq) + 8H2O (l)
In an acidic solution, Cr2O72- reacts with hydrogen peroxide to form diperoxochrome(VI) oxide, [Cr(O2)2O]. Cr3+ is precipitated out of diperoxochrome(VI)oxide by hydrogen ions.
Cr2O72−(aq) + 4H2O2 (aq) + 2H+(aq) ———> 2[Cr(O2)2O] (aq) + 5H2O (l)
2[Cr(O2)2O] (aq) + 2H+(aq) ———> Cr3+(aq) + 3O2 (g) + 2H2O (l)
Reaction with hydroxide
Hydroxide ions will precipitate amphoteric Cr3+ in the form of Cr(OH)3. The reaction is as follows:
[Cr(H2O)6]3+ (aq) + OH− (aq) ———> Cr(OH)3(H2O)3 (s) + H2O (l)
Cr(OH)3(H2O)3 (s) + OH− (aq) ———> [Cr(OH)6]−(aq) + H2O (l)
FAQs
Why is Cr+ more stable than Cr?
Cr+ is in a lower energy state than Cr which makes it more stable. The more electrons chromium loses, the more stable it becomes.
For instance, Cr3+ is more stable than Cr2+ because it has half-filled t2g orbitals. The electronic configuration [Ar]3d3 is more stable than [Ar]3d5.
Does Cr form anions?
Chromium is not likely to form anions by itself, at least not readily. But in compounds like chromate (CrO42−), a chromium oxoanion, it exists in an anion.
What type of bonds does chromium form?
Chromium, by itself, consists of metallic bonds. But it can also form covalent and ionic bonds when it reacts with other elements.
Two chromium atoms will form covalent bonds because they share electrons. But it forms ionic bonds in compounds where it loses electrons.
Conclusion
Chromium may have +1, +2, +3, +4, +5, or +6 charges, depending on how it reacts. But the +2, +3, and +6 charges are the most common. The less common charges exist in rare chromium compounds. They are also not as stable as the common charges.
Chromium is more likely to form a cation than an anion. Chromium anion is usually seen as a compound of chromium, chromium oxoanion (CrO42−). Besides these, you will find only chromium cations.
You can also learn about the charge of tin, another metal that exhibits more than one charge.
Thanks for reading.