Electronic Configuration, General Properties, Hydrides and Oxides in Group 16 Elements of Periodic Table

Group 16 Element

Group 16 elements has five elements namely Oxygen(O), Sulphur(S), Selenium(Se), Tellurium(Te) and Polonium(Po).

- They are named as Oxygen family.

- The first four members are non – metals are called Chaleogens.

- Oxygen is most abundant element, Sulphur is less abundant and others are comparatively rare.

Electronic Configuration

Element	Aomic Number	Electronic Configuration
O	8	[He] 2S² 2P⁴
S	16	[He] 3S² 3P⁴
Se	34	[Ar] 3d¹⁰ 4S² 4P⁴
Te	52	[Kr] 4d¹⁰ 5S² 2P⁴
Po	84	[Xe] 4f¹⁴ D¹⁰6S² 6P⁴

The general outer electronic configuration of group 16 elements is ns² nP⁴.

General Properties of Groupb16 Elements

1.:- Atomic Radius:-

It increases gradually with increase in atomic number.

2.:- Melting and Boiling Points:-

It increases regularly with increase in atomic number.

3.:- Ionization Potential:-

Ionization energy of the first element Oxygen is very high. The values for the further elements decreases on moving down the group.

4.:- Metallic & non – metallic character:-

The first four elements are non – metals but non – metallic character is stronger in O & S and weaker in Se & Te. The last element Po is a distinctly metal.

5.:- Oxidation States:-

O	-1, -2, +2
S	-2, +2, +4, +6
Se	-2, +2, +4, +6
Te	-2, +2, +4, +6
Po	+2, +4

All the elements have nS² nP⁴ configuration in their outer shell. These elements tend to gain two electrons to attain a noble gas configuration. They shows -2 oxidation state(H₂O).

- Oxygen form F₂O. The oxidation state of O is +2. The oxidation state of O H₂O₂ is -1.

- S, Se, Te also shows -2 & +2 oxidation state.

- Po shows +2 oxidation state.

- Excepting O all the elements have vacant d orbitals in their valency shells and they shows +4 & +6 oxidation state.

6.:- Catenation:-

The first two elements O & S shows the property of catenation.

H – O – O – H, H – S – S – H, H – S – S – S – H.

7.:- Allotropy:-

- All the elements of group 16 shows allotropy. Thus Oxygen exists in two allotropic form O₂ & O₃.

- Sulphar occurs in a number of allotropic form

i.e.

o Rhombic or α – Sulphur

o Monoclinic or β – Sulphur

o Plastic or γ - Sulphur

o Colloidal or δ - sulphur

o λ Sulphur

o μ Sulphur

- selenium exists in two forms:- Red form and Gray form.

Hydrides of group 16 elements

A):- Hydrides of formula H₂R

All the members of oxygen family form hydrides like H₂R.

i.e. H₂O, H₂S, H₂S, H₂Se, H₂Te, H₂Po.

Preparation:- The hydrides of oxygen(Water) is available in abundance in nature. The hydrides of S, Se, Te, are obtained by the action of acids on metal Sulphides, metal Selenides and metal Tellurides.

Fe + H₂SO₄ → FeSO₄ + H₂S

K₂Se + H₂SO₄→ K₂SO₄ + H₂Se

Properties

1.:- Boiling Points:-

Boiling points decreases from H₂O to H₂S and then increases.

H₂O	H₂S	H₂Se	H₂Te	H₂Po
100⁰C	-60.75⁰C	-41.5⁰C	-1.8⁰C	-

Abnormally high points of water is due to the association of molecules through hydrogen bonding.

2.:- Acidic Character:-

All the hydrides of group 16 are weak acids and dissociate to varying degrees to give H⁺ ions.

The acidic character increases with increase size of the central atoms.

H₂O ˂ H₂S ˂ H₂Se ˂ H₂Te ˂ H₂Po

3.:- Thermal Stability:-

The thermal stability of the hydrides decreases with rise in molar mass.

H₂O ˃ H₂S ˃ H₂Se ˃ H₂Te ˃ H₂Po

4.:- Reducing Character:-

All the hydrides except water are reducing agents. The reducing character increases on moving from H₂S to H₂Te

H₂S ˂ H₂Se ˂ H₂Te

5.:- Complex forming Capability:-

Hydrides of Oxygen(H₂O) has tendency to form complexes is very high, but H₂S has much lower tendency to form complex than H₂O.

6.:- Bond Angle:- Bond angle decreases with decrease in electronegativity of the central atom.

H₂O	H₂S	H₂Se	H₂Te
104.5⁰	92.5⁰	90.0⁰	89.0⁰

B):- Hydride of formula H₂R₂:-

Ø The first two members of the family forms hydrides of the formula H₂R₂(H₂O₂, H₂S₂)

However these two hydrides differ from each other H₂O₂ is stable and H₂S₂ is unstable.

Ø H₂O₂ acts as a strong oxidizing agent and H₂S₂ does not.

Ø H₂O₂ is highly associated due to hydrogen bonding whereas H₂S₂ form discrete molecule.

Ø Both the hydrides have similar non – planar skew structure.

Oxides of Group 16 Elements

The elements of group 16 forms several oxides as shown in table:

Name	Sulphur	Selenium	Tellurium	Polonium
Monoxides	SO	-	TeO	PoO
Dioxides	SO₂	SeO₂	TeO₂	PoO₂
Trioxides	SO₃	SeO₃	TeO₃	-
Heptaoxides	S₂O₇	-	-	-

Ø Oxides of sulphur are more stable than the corresponding oxides of other elements. Thus SO₂ and SO₃ are more stable than corresponding dioxides and trioxides.

Ø Heptoxide formed only by Sulphur.

a):- Monoxide:- All elements except Selenium forms Monoxides.

Ø I.e. SO, TeO, PoO.

Ø SO is formed by passing electron discharge through sulphur dioxide.

Ø Tellurium and Polonium Monoxide are formed by heating the corresponding trioxides.

b):- Dioxides:-

All the members of oxygen family except O form dioxides of the formula MO₂(SO₂, SeO₂, TeO₂ and PoO₂). These differ from one another considerably in their properties and structure.

Ø SO₂:-

It is gas and forms discrete molecule even in the solid state.

SO₂ is acidic oxides and are soluble in water.

Structure of SO₂

Out of the three SP² hybrid orbitals of S, one is occupied by a lone pair of electrons. Remaining two hybrid orbitals overlap with one of P orbital of each of the two Oxygen atoms forming sigma bond. This gives rise to bent structure.

Ø SeO₂:-

It is white volatile solid.

In the gaseous state, SeO₂ exists in Monomeric form.

In solid state it has Polymeric structure.

It is acidic oxide.

Ø TeO₂ and PoO₂:-

These are non – volatile crystalline ionic solids. It is amphoteric

SO₂ and SeO₂ are acidic oxides and are soluble in water. TeO₂ and PoO₂ are amphoteric oxides and insoluble in water. Thus acidic character of dioxides decreases as we move down the group.

c):- Trioxides:-

Among the trioxides SO₃ is most important. SeO₃ and TeO₃ are also known. They all are acidic in natue and dissolve in water to give acids.

SO₃ + H₂O → H₂SO₄ Sulphuric Acid

SeO₃ + H₂O → H₂SeO₄ Selenic Acid

Ø The strength of the acid drcreases on moving down the group i.e. SO₃ ˃ SeO₃ ˃ TeO₃

Ø The trioxides, in gaseous state are known to have planar trigonal structure formed by SP² hybridisation of S orbitals.