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# Oxygen Family

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 Sub Topics The elements oxygen, sulfur, selenium, tellurium and polonium constitute group VI A of periodic table. In the long form of periodic table they find place in group 16 and p-block elements. The first four are nonmetals and are called the chalcogens - meaning one forming elements because a large number of metal ores are oxides or sulphides.Atoms of these elements have the outer electronic configuration as ns2np4. In this group only sulfur has a strong tendency of catenation. Oxygen also shows this tendency to some extent. All these elements belong to p-block elements. Polonium has metallic character and it is a radioactive material with very short period.

## Preparation of Oxygen

English scientist named Joseph Priestley in 1774 discovered oxygen by heating mercuric oxide in an enclosed container with a magnifying glass. That mercuric oxide decomposes into oxygen and mercury.

Oxygen is usually prepared in the lab by heating an easily decomposed oxygen compound such as potassium chlorate (KClO3). The equation for this reaction is

2KClO3 + MnO2 $\rightarrow$ 2KCl + 3O2(g) + MnO2

The laboratory setup for preparation of oxygen is shown below.

Oxygen is a gas under ordinary conditions of temperature and pressure and it is a gas that is colorless, odorless, tasteless and slightly heavier than air, all these physical properties are characteristic of this element.

## Compounds of Oxygen

Oxygen in organic compound can occurs in a variety of forms in nature. The list of oxygen compounds are alcohols, ethers, phosphates, aldehydes, ketones, amide, esters, oxides, carbonyl compounds etc. Oxygen compounds are given in the below table with their general formula.

 S.No Compounds General formula 1 Alcohols R-OH 2 Ethers R–O–R 3 Phosphates (HPO3)x 4 Aldehydes RCHO 5 Ketones R-CO-R 6 Amide RC(O)NHR' 7 Esters RCOOR' 8 Oxides M2O

## Physical Properties Of Oxygen

The physical properties of oxygen family are listed below.
1. Density - The density increases down the group with the increase in atomic number.
2. Melting point and boiling point - It shows a regular increase down the group.
3. Ionization energy - These elements possess large values on ionization energies which decreases gradually from O to Po. The decrease in ionization energy from oxygen to polonium is due to increase in size of the atoms and increase in screening effect of the electrons belonging to lower shells.
4. Metallic and non-metallic character - Metallic character depends on ionization energy. Lesser the ionization energy greater will be the metallic character. As we move down the group the ionization energy decreases and therefore the metallic character increases.
5. Catenation - In this group only S has a strong tendency of catenation. Oxygen also shows this tendency to a limited extent.
6. Oxidation state - Oxygen being first member in this group shows -2 oxidation state in its compounds owing to its high electronegativity. It also exhibit -1 in H2O2 and zero in O2. Unlike oxygen the other elements have a tendency to show +2, +4 and +6 oxidation states.
7. Multiple bond formation - The tendency of these elements to form multiple bonds to carbon and nitrogen decreases as we move down the group from sulfur to tellurium.
8. Electron affinity - These elements have high electron affinity and on moving down the group the size of the atom increases and distance of valence shell from nucleus increases. The additional electron feels lesser attraction as we move down the group and hence electron affinity decreases.
9. Electronegativity - Oxygen is strongly electronegative in character. The value of electronegativity decreases with increase in atomic number down the group. This is due to increase in size of the atoms and decrease in effective nuclear charge as we move down the group.
10. Elemental state - Oxygen exist in a diatomic gaseous state at room temperature while other elements are solids.
11. Allotropy - All elements of the group exhibit allotropy. Oxygen exists in diatomic and triatomic states. Sulfur is found as rhombic, plastic and colloidal sulfur. Selenium has rhombic, mono clinic and grey forms. The grey form is the most stable form and consists of regularly arranged spirals of selenium atoms.

## Chemical Properties Of Oxygen

Oxygen family properties are listed below.

Formation of hydride

All the elements of this group form hydride of the general formula H2M. The formation of hydride is shown below.

M + H2 $\rightarrow$ MH2

For example, the list of hydride formed by this group elements are H2O, H2S, H2Se, H2Te etc. The melting point, bond angle and thermal stability of these hydride decreases down the group.

H2O > H2S > H2Se > H2Te

The reducing nature, bond length and acidic nature of these hydride increases as we move down the group.'

H2O < H2S < H2Se < H2Te

Formation of halides

All the elements form halides. Since fluorine is more electronegative than oxygen, its compounds with oxygen are called fluorides. The general preparative routes for chalcogen halides involve the direct reaction of the chalcogen with respective halogen.

$\frac{1}{4}$S8(l) + Cl2(g) $\rightarrow$ S2Cl2(l)
Te(s) + 2Cl2(g) $\rightarrow$ TeCl4(s)

The difluorides of oxygen cannot be written as F2O instead it is written as OF2.

Formation of oxides

The elements of this group form a number of oxides. Some of the oxides formed by these elements are SO, TeO, PoO, SO2, SeO2, TeO2, PoO2, SO3, SeO3 and TeO3. All elements form monoxide. All elements form dioxide with formula MO2. SO2 is a gas, SeO2 is a volatile solid while TeO2 and PoO2 are non-volatile crystalline solids.

Selenium and tellurium dioxides are solids having polymeric chain. The acidic character of the dioxides decreases as we move down the group.

Formation of oxyacids

The oxyacids of sulfur are more numerous and important than those of Se and Te. The list of oxyacids of sulfur are H2SO4, H2SO3, H2SO5 (Caros acid), H2S2O8 (Marshells acid), H2S2O3, H2S2O6 and H2S2O7. Selenium form selenous acid (H2SeO3) and Selenic acid (H2SeO4) and Tellurium form tellurous acid (H2TeO3) and telluric acid (H2TeO4).

## Oxygen Family Elements

Elements listed below belongs to Group 16 (VI A) of the long form of periodic table. Except Po all other elements are also called chalogens, which means ore or mineral forming elements. Out of all these elements oxygen, sulfur and tellurium are non metals while polonium is a radioactive metal.

Atoms of these elements have the outer electronic configuration as ns2np4, where n varies from 2 to 6.

 S.No Element Atomic number Electronic configuration 1 Oxygen 8 [He]2s22p4 2 Sulfur 16 [Ne]3s23p4 3 Selenium 34 [Ar]3d104s24p4 4 Tellurium 52 [Kr]4d105s25p4 5 Polonium 84 [Xe]4f145d106s26p4

There are two half filled p-orbitals which are used for bonding with other elements. From the similar outer electronic configuration of these elements it is expected that they will show similar physical and chemical properties.

## Oxygen Family Facts

1. Oxygen is the most abundant element (46.5%) in the earth crust.
2. Joseph Priestley obtained oxygen by focusing the sun light on mercuric oxide in 1774.
3. About 21% of the components of dry air consist of O2 molecules.
4. In combined state it is also present in plants and animals tissues.
5. Ozone is the second form of oxygen and considered as its allotrope.
6. It has three isotopes of atomic weight 16, 17 and 18 in the ratio of about 10,000:1:8.
7. Oxygen always exist as diatomic (O2) molecule.
8. With metallic elements oxygen forms ionic compounds.
9. Oxygen reacts with non metals to form a large number of molecular compounds.
10. Only the noble gases and few inactive metals such as Pt and Au do not react directly with oxygen.

## Oxygen Family Name

1. The elements oxygen, sulfur, selenium, tellurium and polonium constitute of group VI A of periodic table.
2. In the long form of periodic table they find place in group 16 and p-block elements.
3. First four members of this group (O, S, Se, Te) are also known as chalcogens from Greek words "chalkos" for copper and "genes" for "born". Most copper minerals are either oxygen or sulfur compounds.
4. Polonium is a radioactive element and is the most metallic in the group.

## Periodic Table Oxygen Family

Group 16 of periodic table contains five elements namely oxygen (O), sulfur (s), selenium (Se), tellurium (Te) and polonium (Po). These elements belong to p-block on the periodic table.
Oxygen is the most abundant element on the earths crust. Sulfur is the less abundant and occurs in free and combined states. Sulfur is also known as Brim stone. All the elements of this group have the outer electronic configuration ns2np4.

## Oxygen Family Reactivity

Oxygen the first member of 16th group differs in its chemical behavior from the other members of its group on account of its small size and high electronegativity. Oxygen and sulfur are very reactive and in general the reactivity decreases down the group. Oxygen practically reacts with almost all the elements and its reactivity is slightly lesser than the reactivity of most reactive element fluorine of group 17.

The reactivity down the group on the periodic table is shown below.

It is thought that due to its extreme reactivity free oxygen was a deadly poison to early life forms on earth. The reactivity of the group VI A elements decreases as one moves down the group.

## Oxygen Family Characteristics

Characteristics of this oxygen family include
1. Oxygen, sulfur and selenium are non metals, tellurium is a semi metal and polonium and ununhexium are radioactive metals. These elements have 6 valence electrons and have an apparent charge of 2-.
2. Oxygen and sulfur are essential to life.
3. Sulfur is distinctive because in its elemental form it is yellow. When burnt it smells like rotten eggs.
4. Selenium and tellurium are slightly toxic. However selenium is used in photoelectric and solar cells. Tellurium is used in electronics and catalyst.
5. Polonium and ununhexium are the radioactive members of the family. It was discovered in 1898 by Marie Curie.