UPSC Chemistry Metals and Non-metals / धातु और अधातु Non - Metal

NON - METALS

Non-metals occupy the upper right hand comer of the periodic table.

Seventeen elements are generally classified as non-metals. Their names as per their states in the normal conditions are:

Gases: hydrogen, helium, nitrogen, oxygen, fluorine, neon, chlorine, argon, krypton, xenon and radon.

Liquid: bromine.

Solid: carbon, phosphorus, sulphur, selenium, and iodine.

PROPERTIES OF NON-METALS

Physical Properties

• Non-metals are neither malleable nor ductile.
• They are brittle (break easily).
• They do not conduct heat and electricity.
• They are not lustrous (not shiny). They are dull.
• They are generally soft (except diamond which is extremely hard non-metal).
• They may be solid, liquid or gases at the room temperature.
• They have comparatively low melting points and boiling points (except diamond which is a non-metal having a high melting point and boiling point).
• Non-metals have low densities, that is, non-metals are light substances.
• Non-metals are non-'sonorous. They do not produce sound when hit with an object.

Chemical Properties of Non-Metals

Non-metals are more reactive with metals than with other non-metals. Generally non-metals react with each other at a high temperature.

Action of Air:

Non-metals do not react with air at room temperature except white phosphorus.

Action of water:

Generally, non-metals do not react with water. However, chlorine dissolves in water and form an acidic solution.

Displacement of one non-metal by another from salt solution:

Just like metals, non-metals also differ in their reactivity’s. Among halogen family (i.e. Cl, Br, I and F) the most reactive is chlorine (Cl). The order of reactivity is Cl > Br > I. Thus chlorine can displace Br and I from solutions of bromides (NaBr) and Iodides (Nal).

Reaction with metals:

Non-metals with high electronegativity (F, Cl, Br etc.) generally reacts with alkali and alkaline earth metals to form ionic compounds.

Handy Facts

Allotropes are different from of the same element. Different bonding arrangements between atoms result in different structures with different chemical and physical properties. For example: The all tropes forms of carbon are white, red and black phosphorous. The term allotropy is referred to element only another term polymorphism is used to mean the ability of solid to exist in more than one term or crystal structure.

SOME IMPORTANT NON-METALLIC ELEMENTS

Hydrogen

The discovery of hydrogen is credited to Henry Cavendish in 1766, although it had been isolated as early as 1671 by Robert Boyle.

Isotopes of Hydrogen

Three isotopes of hydrogen exist and all occur naturally.

• \[^{\text{1}}\text{H}\]is sometimes called Protium, It is abundent in nature. It is the only hydrogen isotope lacking neutrons.
• The second isotope, \[^{2}\text{H}\], is called deuterium

Handy Facts

D-element bonds are more difficult to break than H-element bonds and this fact allows the mechanisms or many chemical reactions to be examined. \[{{D}_{2}}O\]itself is important as a material that slows neutrons in nuclear reactors.

• The third isotope,\[^{3}\text{H}\], Tritium is radioactive.

Properties

• Hydrogen occupies a unique place in the periodic table, and while it usually appears above the alkali metals or the halogens (or both), its properties don't fall well within either group.
• The ionization energy of hydrogen is much higher than any of the alkali metals.
• Hydrogen is a colorless, odorless, tasteless gas at ambient temperature. It has very low boiling and melting points (only helium boils colder). It is poorly soluble in most solvents.

Uses

• Over two-thirds of this hydrogen produced is used to prepare ammonia (\[N{{H}_{3}}\]) by the Haber process. The large majority of this ammonia is then used in fertilizer production.
• Methanol, which is an industrially important compound, is prepared from the reaction of hydrogen with carbon monoxide:

Group 18: Noble Gases

• The elements in Group 18 are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn).
• All Group 18 elements are gases at room temperature.
• They are completely chemically inert with few exceptions.
• The first noble gas compound was prepared in 1962 by scientist Neil Bartlett. Bartlett noticed that the ionization energy of xenon is about the same as that of oxygen.

• Group 17: Halogens

The halogens are fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (Ats).

• Fluorine typically occurs in nature in minerals such as fluorite (fluorspar,\[Ca{{F}_{2}}\]). The other halogens are generally isolated from salts dissolved in seawater. They are obtained by oxidation of the halide ion to the halogen in a molten salt, except fluorine which requires special conditions to prevent explosions.
• All halogens have high electron affinities and ionization energies. .

Uses of halogenated compounds

• Teflon- non-stick coating, is a polymer made of carbon and fluorine\[(C{{F}_{3}}(C{{F}_{2}})n(C{{F}_{{{2}^{-}}}}C{{F}_{{{2}^{-}}}})\], n is very large).
• The compounds used in air-conditioners (now HCFCs) are compounds made up of carbon, fluorine, hydrogen, and chlorine (e.g. \[HCFC-22:CH{{F}_{2}}Cl\]). These substances are more environment friendly than the Freons. (HCFCs are Freons in which either a chlorine or fluorine atom has been replaced by a hydrogen atom to allow easier environmental degradation to occur.)
• Many plastics, organic solvents, pesticides, fungicides, and bactericides contain chlorine atoms. Chlorinated compounds are also used as disinfectants and bleaching agents.

Group 16: Chalcogens

• The elements of the Group 16 of the periodic table are Oxygen (0), Sulphur(S), Selenium (Se), Telurium (Te) and Polonium (Po) which are also called
• Oxygen is the second most abundant element in the Earth’s crust and in hydrosphere.
• Two allotropes of oxygen are;\[{{O}_{2}}\]: Oxygen and \[{{O}_{3}}\]: Ozone. Both occur naturally. Oxygen has a high electron affinity, electronegativity, and ionization energy. It tends to form compounds in the -2 oxidation state, although compounds with -1, -1/2, and + 2 oxidation states also exist (in\[{{H}_{2}}{{O}_{2}},K{{O}_{2}},\] and\[O{{F}_{2}}\]respectively).
• \[{{O}_{2}}\]is an odorless, colorless, and tasteless gas at room temperature. It is quite reactive and form oxide ions or strong covalent single bonds to other elements. Oxygen is obtained by the fractional distillation of air.
• Ozone is a pale blue gas with an irritating odor. It is a significantly stronger oxidant than Di oxygen\[({{O}_{2}})\] because of its structure. Small amounts of ozone are generated by lightning striking the earth. We can even smell this ozone also. Internal combustion engines (cars, trucks, etc.) produce large quantities of ozone that frequently affect air quality in cities.

Handy Facts

The word oxygen comes from the Greek meaning ‘acid former,’ while ozone comes from the Greek meaning ‘to smell.’

Water (\[{{H}_{2}}O\]):

Water is the most abundant molecule on the earth. Approximately 70% of the Earth’s surface is water. Water is also the only substance on Earth which naturally occurs in a solid, liquid and gas form. Water is also medium for many chemical reactions. That is why it is called “universal solvent”.

Hardness of Water

Hardness of water is due to dissolved sulphate, chloride or carbonate salt of calcium and magnesium. There are two kinds of hardness of water.

• Temporary
• Permanent

Temporary hardness is due to dissolved bicarbonate salt of calcium and magnesium. Temporary hardness can be removed by boiling. Boiling causes formation of carbonate from the bicarbonate.

Permanent hardness is caused by chlorides and sulphate of calcium and magnesium. Permanent hard water can-not be softened by boiling.

Though hard water is not considered harmful for drinking, it may cause other harms. Hard water can leave the clothes rough and worn out. More soap is required for washing clothes.

Properties of Water

• It is attracted to other polar molecules. This is also called adhesion. Adhesion leads to occurrence of capillary action.
• Water has high specific heat and high heat of vaporisation because of this water is used as coolant in moter vehicles
• It has high heat of evaporation. This property is responsible for its ability to resist evaporation in moderate temperature.
• Ice has lower density compared to water. This low density allow icebergs to float and is also the reason that only top part of the lakes are frozen.
• Water has high polarity. This makes water a powerful solvent as it attracts other less and polar molecules.

Group 15: Nitrogen

• Nitrogen is rare in the hydrosphere and lithosphere, though abundant in the atmosphere. Only \[NaN{{O}_{3}}\] and \[KN{{O}_{3}}\]are found in significant amounts as mineral deposits.
• Compounds of nitrogen occur in all oxidation states from -3 to +5. In this property, nitrogen differs from all other second-row elements except carbon which have very limited numbers of accessible oxidation states.
• Diamond consists of an infinite array of tetrahedral carbon atoms. It is the hardest naturally occurring substance and pure diamond is a colourless crystalline material. It is a very soft, black material that is quite slippery and is a good electrical conductor.

Group 14: Carbon

• Carbon has been known since pre-historic times. Carbon ranks only 17^th amongst all elements (between sulphur and zirconium) in abundance in the Earth’s crust.
• Carbon is one of the elements which shows allotropy.

Carbon-monoxide (CO)

• Carbon monoxide (CO) is a colorless, odorless, tasteless gas with a relatively low boiling point.
• It forms when carbon or hydrocarbons bum in a deficiency of oxygen.
• It is toxic in either high doses or prolonged (hours) exposure to low doses. Its toxicity arises because it binds to haemoglobin much like oxygen does, but more strongly

Uses:

• Industrially, carbon monoxide is sometimes used as a fuel because it bums to carbon dioxide.
• It also is a valuable reducing agent. When reacted with hydrogen it generates methanol, an important organic solvent and basic reagent.

Carbon-dioxide (\[\mathbf{C}{{\mathbf{O}}_{\mathbf{2}}}\])

• Like carbon monoxide, carbon dioxide (\[C{{O}_{2}}\]) is colourless, odourless, and tasteless.
• It is much less toxic than CO, but will induce unconsciousness and death at very high concentrations even if it is not inhaled.
• Carbon dioxide is absorbed by plants in the presence of sunlight and chlorophyll (green colouring matter) to form glucose and higher carbohydrates. This process is known as

Uses: The two major uses of carbon dioxide are as a refrigerant and for carbonating soft drinks.

Carbonic Acid and Carbonates

When \[C{{O}_{2}}\] dissolves in water, the weak acid, i.e. carbonic acid (\[{{H}_{2}}C{{O}_{3}}\]) forms.

• Carbonate minerals are plentiful in nature and include aragonite (\[CaC{{O}_{3}}\]), calcite (\[CaC{{O}_{3}}\]), dolomite (\[CaMgC{{O}_{3}}\]), gaylussite \[(N{{a}_{2}}Ca{{(C{{O}_{3}})}_{2}})\], lanthanite \[({{(La,Ce)}_{2}}{{(C{{O}_{3}})}_{3}})\] magnesite (\[MgC{{O}_{3}}\]), and witherite (\[BaC{{O}_{3}}\]). Of the minerals, the calcium and magnesium containing varieties are most important.
• In particular, the stalactites and stalagmites in caves are composed of calcium carbonate are coral reefs.

Science in Action

Elemental silicon is a semiconductor and very pure material (99.9999%). It is used in the production of computer chips.

Glass

• Glass is simply quartz to which one or more other substances have been added. Because of this added substance, the temperature at which the quartz melts is lowered. This is important because quartz melts near \[1000{}^\circ C\]and getting flames that hot is very difficult.
• Common glass (also soft glass or soda-lime glass) is prepared by adding calcium carbonate and sodium carbonate to molten quartz. The heat drives carbon dioxide off, leaving calcium oxide and sodium oxide behind.
• Lead crystal results from adding lead oxide to quartz. The extra mass of the lead gives high quality crystal its heavier feel and the high refractive index that gives crystal its special look.
• Pyrex is obtained by adding boron oxide,\[{{B}_{2}}{{O}_{3}}\], to quartz. This causes its coefficient of thermal expansion to decrease. Baking dish made of pyrex glass when moved from freezer to the oven do not crack. Also, stovetop cookware is possible with borosilicate glass, because it won't crack or melt under normal kitchen conditions.
• Coloured glass results from the addition of transition metal ions to the glass. The metal usually exists as an oxide in the structure. Examples are:

Science in Action

Use of some other non-metals are given below:

• Sulphur is used in making compounds like sulpha drugs, sulphuric acid, in matches, in gun powder, for vulcanization of rubber, etc.
• Boron, in the form of compound borax, is used in making skin ointments.
• Phosphorus is used in making crackers.
• Chlorine, in the form of bleaching powder, is used for purification of water.
• Carbon is used as a fuel, as electrodes (graphite), as a reducing agent in metallurgy.
• Oxygen, hydrogen and nitrogen are used by all living things; they are the ‘building blocks’ of life.
• Iodine is used to prevent thyroid problems..
• Bromine is used in the preparation of dyes.
• Some compounds of fluorine (such as sodium fluoride, stannous fluoride) are added to toothpastes to prevent dental decays or formation of cavities.