Password must be atleast 8 characters long. Signup now to download free sample papers and notes. Already have an account? By filling this form you agree to our Terms and Conditions. Launch Your Course Log in Sign up. Menu Classes. Competitive Exam. Class Notes. By volume, dry air contains The amount of sulphur in the earth's crust, on the other hand, is merely 0.
In volcanoes, traces of sulphur appear as hydrogen sulphide. In sulphide ores, selenium and tellurium are found as metal selenides and tellurides. Polonium is a decay product of thorium and uranium minerals found in nature. Atomic and ionic radii rise from top to bottom in the group as the number of shells increases. The size of oxygen atoms, on the other hand, is extremely small.
The enthalpy of ionisation decreases as you progress through the group. It's because of the growth in size. In the corresponding periods, however, the elements of this group have lower ionisation enthalpy values than those of group This is owing to the additional stable half-filled p orbitals elelctronic configurations found in group 15 elements. The negative electron gain enthalpy of oxygen is lower than that of sulphur due to its compact structure.
From sulphur onwards, the value grows less negative until it reaches polonium. Oxygen, along with fluorine, has the greatest electronegativity value of all the elements. With an increase in atomic number, electronegativity decreases within the group. This means that from oxygen to polonium, the metallic character increases. Sulphur and oxygen are non-metals, while selenium and tellurium are metalloids, and polonium is a metal.
Polonium is a radioactive element with a short half-life Half-life All of these elements are allotropic. The melting and boiling points rise as the atomic number decreases in the group.
The bigger disparity in melting and boiling temperatures between oxygen and sulphur can be explained by their atomicity; oxygen is made up of diatomic molecules O2 , whereas sulphur is made up of polyatomic molecules S8. Oxidation states and chemical reactivity trends: Group 16 elements have a variety of oxidation states.
The stability of the oxidation state reduces as you progress through the group. Polonium rarely exhibits oxidation states of Because of its tiny size and high electronegativity, oxygen, like other members of the p-block present in the second period, exhibits unusual behaviour. Because oxygen lacks d orbitals, its covalency is limited to four, and it rarely exceeds two in practise. In the case of other group members, however, the valence shell can be enlarged, and covalence approaches four.
Table lists some of the features of hydrides. The decrease in bond H-E dissociation enthalpy down the group can explain the increase in acidic character. Both forms of oxides have an acidic pH. Hexafluorides are the only stable halides among the hexahalides.
In nature, all hexafluorides are gaseous. They are octahedral in shape. These fluorides contain sp3d hybridisation and so have a trigonal bipyramidal structure with a lone pair of electrons in one of the equatorial positions. See-saw geometry is another name for this type of geometry. Except for selenium, all elements create dichlorides and dibromides. The tetrahedral structure of these dihalides is due to sp3 hybridisation. The disproportionation of these dimeric halides is as follows:. It is distinguished from the other members of the VIth group by the following characteristics.
A small size. B high electronegativity and. C non-availability of d-orbitals. Liquefaction of air followed by fractional distillation yields oxygen. Gas that is colourless, odourless, and tasteless. It has allotropy and is paramagnetic. Although oxygen does not burn, it is a powerful promoter of combustion. They generate oxyacids when they dissolve in water, e. They either dissolve in water to form alkalies, react with acids to form salts, or react with acidic oxides to form salts.
They do not produce salts when combined with acids or bases. These can react with both acids and bases, for example. They have the properties of a combination of two simple oxides.
For eg. It's made by sending a quiet electric discharge through dry, pure oxygen. The device used for this is known as an ozoniser. As a result, ozone is a powerful oxidising agent in acidic environments. The formation of this molecule is concrete evidence for I2's basic nature i. When silver objects come into touch with ozone, they turn black. As a result, ozone is a more powerful oxidizer than hydrogen peroxide.
Ozonides are formed when alkenes and alkynes react with ozone. Potassium ozonide, an orange-colored compound, is formed. Hydrogen Peroxide H2O2. According to the following equation, it behaves as a weak acid. A In Acidic Medium. B In Alkaline Medium.
In washing powder, it's used as a brightener. It operates as a reducing agent in the presence of a strong oxidising agent. Its reducing nature is stronger in alkaline solution than in acidic medium. When this reaction is carried out in the dark, it causes light to be emitted yellow coloured.
Chemiluminescene is a type of chemiluminescene. Sulphur S. Sulphur Allotropic Forms. Sulphur exists in a variety of allotropes, the most prominent of which are yellow rhombic - sulphur and monoclinic - sulphur. At ambient temperature, rhombic sulphur is stable, but when heated over K, it transforms into monoclinic sulphur. This allotrope has a yellow colour, a melting point of It is insoluble in water but soluble in benzene, alcohol, and ether to some extent. It has a melting point of K and a specific gravity of 1.
It dissolves in CS2. Sulphur in this form is made by melting rhombic sulphur in a dish and chilling it until a crust forms. The remaining liquid is poured out through two holes in the crust. Colorless needle-shaped crystals of - sulphur occur after the crust is removed. Above K, it is stable, but below that temperature, it converts into - sulphur. Both types are stable around K. This is referred to as the transi. S8 molecules can be found in both rhombic and monoclinic sulphur. These S8 molecules are crammed together to form a variety of crystal shapes.
In both variants, the S8 ring is puckered and has a crown shape. Figure 1 shows the molecular dimensions temperature. In the previous two decades, several additional sulphur modifications with sulphur atoms per ring have been synthesised.
According to the following reaction, it eliminates chlorine from the surface of fibres during dyeing. As a result, it is referred to as antichlor. If you have too much hypo, you'll get a soluble complex. When hypo is employed as a fixer in photography, this reaction is used. It takes on a pink or violet hue, which fades quickly as the reaction progresses.
In graphite, carbon is SP2-hyberdized graphite has a two-dimensional sheet like structure consisting of a number of hexagonal rings fused together. Graphite conducts electricity along the sheet.
It is very soft and Slippery FullerenceFullerence was discovered collectively by three scientists namely R. E Smalley,R. F Curl and H. It I prepared by direct oxdisation of C in limited supply of oxygen. It is prepared by complete combustion of carbon and carbon fuels in excess of air. Each silicon atom is covalently bonded in a tetrahedral manner to four oxygen atoms. The basic structure of silicates is SiO 4 4.
Zeolites are used to remove permanent hardness of water. Copyright ncerthelp. Element Symbol Atomic No. Follow Us On Facebook. Please Share this webpage on facebook, whatsapp, linkdin and twitter. Trihalides: These are covalent compounds and become ionic down the group with hybridisation, pyramidal shape.
They are lewis acids because of the presence of vacant d — orbitals. They possess hybridisation and hence possess trigonalbirpyamidal shape. PCl5 is ionic in solid state and exist as In PCl5, there are three equatorial bonds and two axial bonds. The axial bonds are longer than equatorial bonds because of greater repulsion from equatorial bonds.
Nitrogen does not form pentahalides due to absence of d — orbitals.
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