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Periodic table

s-elements

p-elements

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S [He]2s22p4 Se [Ne] 3s23p4 Te [Ar] 4s24p4 Po [Kr] 5s25p4

Chalcogens

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Properties Of Chalcogens

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Oxidation State

Compounds Of Chalcogens. Chemical And Physical Properties Overview

S

Se

Te

Po

-2

H2S

H2Se

H2Te

H2Po

S2-

Se2-

Te2-

Po2-

Me2S

Me2Se

Me2Te

Me2Po

-1

H2Sn, Me2Sn

H2Sen, Me2Sen

H2Ten, Me2Ten

0

Sn

Sen

Ten

Po

1

S2Cl2

2

PoX2 (PoCl2...)

PoH2

3

S2O42-

S2O42-

4

SO2

SeO2

SO2

PoO2

SO32-

SeO32-

TeO32-

PoX4

5

S2F10

6

SF6

PoO3

SO3

SeO3

TeO3

PoX6

SO42-

SeO42-

TeO42-

SO2Cl2

Electron configurations of chalcogens

The p-elements of group VI of the Periodic system are named chalcogenes (from the Greek words «copper» and «born») because most copper ores consist of substances which contain oxygen or sulfur and some admixtures of Se and Te, for instance, chalcosine (Cu₂S), chalcopyrite (СuFеS₂).

Electronic configuration of the last energy level of sulfur is 3s²3p⁴.

O     S, Se, Te, Po    

The six valence electrons are located at 3s- and 3р-sublevels. Sulfur atoms use two unpaired electrons to form two covalent bonds. A transition of s- and p-electrons to free d- and even 4s-orbital becomes possible at the excitation of atoms. For example, transition 3s²3p⁴  3s²3p³4s¹ requires 627.0 kJ/mol energy. This energy is by +250.8 kJ/mol lower than in case of oxygen. Therefore, such transition can be realized.

Thus, besides one-electron orbitals 3s-, 3р-orbitals, and vacant 3d-orbitals can take part in the formation of chemical bonds of sulfur. It signifies that the valence of sulfur can vary from 2 to 6.

Sulfur is a typical non-metal. Its electronegativity value (EN = 2.5) is lower than EN of halogens, oxygen and nitrogen. Attaching two electrons, sulfur achieves completion of 3р-sublevel with the formation of stable noble gas electronic configuration of Ar, 3s²3p⁶. Therefore, oxidation state -2 is characteristic of sulfur. Therefore, natural minerals of chalcogens are usually chalcoginides (sulfides, selenides etc.).

The highest oxidation state +6 corresponds to the state when sulfur forms six covalent bonds with more electronegative elements. Thus, the following characteristic oxidation states of sulfur exist: -2, 0, 2, +4, +6.

An electronic configuration of the last energy level is ns²np⁴. To form chemical compounds Se and its analogues use unpaired electrons, and also one or two electronic pairs.

Moving downwards to polonium, there is a general tendency among the groups of p-elements: diminishing stability of high oxidation states. Oxidation state +6 has no significance in case of Po due to the large energy gap between ns- and np- sublevels that makes it difficult for ns-electrons to participate in the formation of chemical bonds:

Energy gap between ns- and np- sublevels of VIA group of the Periodic table

	O	S	Se	Te	Po
Еns/np-sublevels, еV	14.9	9.8	10.4	8.8	12

As shown in the table above, the energy gap of Po is similar to the case of oxygen that predetermines instability of its oxidation state +6.

Some physical properties of chalcogens

	O	S	Se	Te	Po
Electronic configuration	[He]2s22p4	[Ne]3s23p4	[Ar]4s24p4	[Kr]5s25p4	[Xe]6s26p4
Allotropes	O2, O3, O4	Monoclinic (S8) rhombic (S8) plastic (S∞)	Red (Se8) Grey (Se), Amorphous (Se)	Hexagonal (Те) Amorphous (Те)	-Po (metal) β-Po (metal)
Ionisation energy of atom, eV	13.62	10.36	9.75	9.01	8.43
Forbidden band energy gap width, eV	insulator	insulator	1.80	0.35	metal
Atomic radius, nm	0.066	0.102	0.116	0.135	0.164
Electronegativity (L. Pauling scale)	3.5	2.5	2.4	2.1
Melting point, С	-218.7	119.3	221	450	254
Boiling point, °C	-182.97	444.6	685.3	990	962
density, g/cm3	1.27 (s)	2.06 (rhombic)	4.81	6.24	9.40
S298, J/(mol•К)	205,03	31,91	42,13	49,5	62,8
Eo, Xo/X2-	1,23	0,142	-0,40	-0,74	-1,0