JEE Chapter - Isolation, Preparation, and Properties of Non-Metals

The periodic table is a grouping of elements that have similar properties. Non-metallic character (holding their own electrons) increases from left to right throughout a period and from down to up across a group.

Non-metals are chemical elements that lack the majority of metallic characteristics, ranging from colourless vapours to gleaming, refractory (high melting temperature) solids. Nonmetal electrons act differently than metal electrons. With a few exceptions, those in nonmetals are set in situ, making nonmetals poor heat and electrical conductors and brittle or crumbly when solid. Metals have free-moving electrons, which is why they are good conductors and can be easily flattened into sheets and drawn into wires. Non-metal atoms have a moderate to high electronegative charge, which causes them to attract electrons in chemical processes and produce acidic compounds.

In nature, some non-metals, such as inert gases (He, Ne, Ar, Kr, Xe), occur free, whereas others, such as oxygen, hydrogen, nitrogen, halogens, and carbon, occur in both free and mixed states. 

Important Topics of Amino Acids and Peptides

• Properties of Dinitrogen 

• Sulphur and its Allotropic  Forms

• Chemical Properties of Metals and Non-metals

General Description of Non-Metals

Non-metal elements are substances that lack the properties of metals. In comparison to metals, the number of non-metals on the periodic table is quite less. Metals are on the left side of the periodic table, whereas nonmetals are on the right. Hydrogen, carbon, nitrogen, phosphorus, oxygen, sulfur, selenium, all halogens, and noble gases are examples of non-metals.

Non-metals are elements that accept or gain electrons to generate negative ions. The outermost shell of non-metals normally has 4, 5, 6, or 7 electrons.

Non-metals are materials that lack all of the characteristics of metals. They are excellent heat and electricity insulators. They are usually gases, although they can also be liquids. Carbon, sulphur, and phosphorus, for example, are solid at normal temperatures.

General Properties of Non-Metals

• High ionization energies and electronegativity are two characteristics of non-metals. Non-metals frequently acquire electrons when interacting with other compounds, forming covalent bonds, because of their features. The anionic dopants have a substantial impact on the valence band among the non-metals. Carbon, nitrogen, fluorine, sulfur, and iodine are non-metal dopants. 

• Non-metal atoms are often smaller than metal atoms. The atomic sizes of non-metals determine the number of other characteristics.

• Electrical conductivities of non-metals are extremely low. The most essential attribute that differentiates non-metals from metals is their low or non-existent electrical conductivity.

• Electronegativities are high in non-metals. This indicates that non-metal atoms have a strong desire to keep the electrons they currently have. Metals, on the other hand, readily give up one or more electrons to non-metals, allowing them to form positively charged ions and conduct electricity.

Physical Properties of Non-Metals

• Non-metals are brittle and break into pieces when beaten. Example: Sulphur and phosphorus.

• Non-metals are not ductile so, they cannot be made into thin wires.

• Non-metals are insulators or poor conductors of electricity and heat because they do not lose electrons to transmit the energy.

• At room temperature, they can be in the state of solids, liquids, or gases.

• They are non-sonorous.

• They can be transparent.

Chemical Properties of Non-Metals

• In the outer shell of non-metals, there are usually 4 to 8 electrons.

• Non-metals have a proclivity for gaining or accepting valence electrons.

• Non-metals react with oxygen to generate acidic oxides when exposed to oxygen. 

• Non-metals are electronegative elements with a strong electronegativity. 

• Non-metal elements are excellent oxidizers. Water has no effect on these elements.

Existence of Non-Metals in Allotropic Forms

• The majority of non-metallic elements can be found in allotropic forms. For example, Carbon is found in graphite and diamond. Physical qualities that are more metallic or less metallic may be found in such allotropes. 

Non-metal halogens and unclassified non-metals include:

• The amorphous semiconducting form of iodine is well recognised.

• The normal state of carbon, graphite, is a decent electrical conductor. The diamond allotrope of carbon is nonmetallic, transparent, and an extremely poor electrical conductor as an insulator.   Other allotropic forms of carbon include semiconducting buckminsterfullerene, as well as amorphous and paracrystalline (mixed amorphous and crystalline) variants.

• Nitrogen can be converted to gaseous tetra nitrogen, an unstable polyatomic molecule with a one-microsecond lifespan. 

• In its usual state, oxygen is a diatomic molecule; however, it also occurs as ozone, an unstable nonmetallic allotrope with an "indoors" half-life of around half an hour, compared to three days in ambient air at 20 °C.

• Phosphorus is remarkable in that as it exists in numerous allotropic forms that are more stable than white phosphorus in its ordinary condition. The most well-known allotropes are white, red, and black; the first is an insulator, while the other two are semiconductors.  Diphosphorus is an unstable diatomic allotrope of phosphorus. 

• Sulfur has the most allotropes of any element. Sulphur amorphous is a metastable combination of these allotropes.

• Boron is found to exist in several crystalline and amorphous forms.

Extraction of Non-Metals

• Hydrogen and helium are thought to account for nearly all of the ordinary matter in the cosmos. Ordinary matter, represented by stars, planets, and living beings, is thought to make up less than 5% of the Universe. Dark energy and dark matter, both of which are poorly understood at the moment, make up the balance.

• The majority of the Earth's atmosphere, oceans, crust, and biosphere are made up of hydrogen, carbon, nitrogen, and oxygen; the other nonmetals have abundances of 0.5 percent or less. In comparison, the metals sodium, magnesium, aluminium, potassium, and iron, as well as a metalloid, silicon, make about 35% of the crust. All other metals and metalloids are abundant in the crust, oceans, and other bodies of water.

• Non-metals are extracted in their natural state from the following sources:

Chlorine, bromine, and iodine are found in brine.

Nitrogen, oxygen, neon, argon, krypton, and xenon are all examples of liquid air.

Boron (borate minerals); carbon (coal; diamond; graphite); fluorine (fluorite); silicon (silica); phosphorus (phosphates); antimony (stibnite, tetrahedrite); iodine (in sodium iodate and sodium iodide); iodine (in sodium iodate and sodium iodide); iodine (in sodium iodate and sodium iodide) while hydrogen, helium, and sulphur in natural gas.

The following procedures are used to extract non-metals from their natural resources in general:

(i) Oxides and halides can be reduced. 

(ii) Salts are reduced electrolytically, for example, Cl2 is reduced electrolytically from a conc. NaCl solution. 

(iii) Thermal decomposition of their hydrides being taking place can also be used to extract non-metals.

Detailed Description of Some of the Non-Metals

Nitrogen

• Nitrogen is distinguished from the other members of this family by its tiny size, strong electronegativity, high ionisation enthalpy, and lack of d orbitals. Nitrogen has a unique capacity to create pπ – pπ multiple bonds with itself and other smaller, electronegativity-rich elements (e.g., C, O). Because the atomic orbitals of heavier elements in this group are too vast and diffuse to overlap effectively, they do not form pπ – pπ bonds.

• Thus, nitrogen is a diatomic molecule having a triple bond between the two atoms (one s and two p). As a result, the bond enthalpy (941.1 kJ mol–1) is quite high. Phosphorus, arsenic, and antimony, on the other hand, form metallic connections in their elemental condition. Because of the significant interelectronic repulsion of the non-bonding electrons and the short bond length, the single N – N bond is weaker than the single P – P connection.

Preparation:

• It can be prepared by heating a mixture of NH4Cl and NaNO2.  In this process, N2is collected by the downward displacement of water. This can be shown as:

NH4Cl + NaNO2   → NH4NO2 + NaCl 

NH4NO2 + Δ → N2+ 2H2O

• Initially, the density increases gradually over time and reaches a maximum someplace for the centre members, before progressively diminishing.

• Industrially, it can be prepared from liquefied air by fractional distillation. The boiling point of N2 is –196oC and that of oxygen are –183oC hence they can be separated.

Properties:

• Reaction with H2 at 200 atm and 500oC, and in the presence of an iron catalyst and molybdenum promoter, N2 combines with H2 reversibly to form ammonia. The process is called Haber’s Process and is the industrial method of manufacturing ammonia. The reaction is exothermic. This can be shown as:

N2 + 3H2 → 2NH3

Uses:

• For providing an inert atmosphere in many industrial processes where the presence of air or O2 is to be avoided.

• For the manufacture of ammonia (NH3)  by Haber’s process.

Phosphorus

• This non-metal is a very reactive species. It randomly catches fire when exposed to air. It occurs in nature in the form of stable phosphates.

Preparation:

Allotropic Forms of Phosphorus:

(i) White or yellow phosphorus (P4)

2Ca3(PO4)2(From bone-ash) + 10C + 6SiO2 → 6CaSiO3+ 10CO + P4(s)

(ii) Red phosphorus: When white phosphorus is heated in the atmosphere of CO2 or coal gas at 573 K red phosphorus is produced. This red phosphorus may still contain some white phosphorus which is removed by boiling the mixture with NaOH where white phosphorus is converted into PH3 gas but red phosphorus remains inert. 

P4+ 3NaOH + 3H2O →PH3(g) + 3NaH2PO2

(iii) Black phosphorus - It has two forms α-black phosphorus and β-black   phosphorous

(a) α-black phosphorus (insulated tube 803K)

P(red) →P(α-black)               

 α-black phosphorous structure is not definite and is a non-conductor of electricity.

(b) β-black phosphorous (At high pressure).

P(white) → P(β-black)

β-black phosphorous is an electrical conductor resembling graphite in this respect and also in its flakiness and lustre. It is insoluble in CS2. It has a layered structure like graphite.

(iv) Brown phosphorus: Above 1600oC, P4 molecule begins to dissociate into P2 molecule. rapid cooling of this vapour gives brown phosphorus which probably contains P2 molecules.

Properties:

• Reactivity of the various allotropic forms of phosphorus towards other substances decreases in the order:

Brown > white > red > black, the last one being almost inert.

Apart from their reactivity difference, all the forms are chemically similar.

Uses:

• Used for drying acidic gases 

• Used as a dehydrating agent

• Used in making smoke signals and producing smoke screens on battle-fields.

Oxygen

• The element oxygen is the most prevalent on the planet. By mass, oxygen makes up 46.6 percent of the earth's crust. By volume, dry air contains 20.946 percent oxygen.

• Because of its compact size and strong electronegativity, oxygen, like other members of the p-block present in the second period, exhibits anomalous behaviour. The occurrence of strong hydrogen bonding in H2 is a good illustration of the impact of small size and high electronegativity. H2S does not include the atom O. Because oxygen lacks d orbitals, its covalency is limited to four, and it seldom surpasses two in practice. In the case of other group members, however, the valence shell can be enlarged, and covalence approaches four.

Preparation:

• The thermal decomposition of oxides of metals leads to the evolution of oxygen gas. This can be shown as-

 3 MnO2 + Δ → Mn3O4+ O2 

             2 Pb3O4 + Δ → 6 PbO + O2

• By the action of conc. H2SO4 on MnO2

             2 MnO2+ 2H2SO4 → 2 MnSO4+ 2H2O + O2

Properties:

• It is a colourless, odourless, and tasteless gas. It is paramagnetic and exhibits allotropy. Three isotopes of oxygen are 168O, 178O, and 188O. Oxygen does not burn but is a strong supporter of combustion.

Uses:

• Used for artificial respiration when oxygen is mixed with helium or CO2.

• Used as an oxidizing agent in rocket fuels in liquid form

• Used for the production of oxy-hydrogen or oxy-acetylene flames employed for cutting and welding.

Solved Examples 

Example 1: Solid PCl5 exists as:

(a) dimer P2Cl10 

(b) [PCl4]+[PCl6]-

(c) (PCl3) (Cl2) 

(d) PCl5 as such

Solution: The correct option is (b) since it exists as-

2PCl5→  [PCl4]+[PCl6]-

Key point to remember: Solid PCl5 exists in ionic forms.

Example 2: The percentage of p-character in the orbitals forming

P–P bonds in P4 are:

(a) 25 

(b) 33

(c) 50 

(d) 75

Solution: Correct option is (d) since P belongs to Group V on the periodic table, one would anticipate the molecule to only be capable of forming three bonds to fill its valence shell. Although phosphorus forms three bonds in P4, the molecular geometry of P4 cannot be characterised by three bonds formed by partly filled p orbitals. P cannot form π bonds due to its higher atomic size, therefore it is tetra-atomic, with each P atom joined to three other P atoms by three sigma bonds. As a result, the p-character plays a 75 percent role in forging P-P bonds in the P4 molecule.

Key point to remember: Phosphorus forms three bonds in P4, the molecular geometry of P4 cannot be characterised by three bonds formed by partly filled p orbitals.

Solved Questions from The Previous Year’s Question Papers

Question 1: White phosphorus on reaction with concentrated NaOH solution in an inert atmosphere of CO2 gives phosphine and compound (X). (X) on acidification with HCl gives compound (Y). The basicity of compound (Y) is

(1) 4

(2) 2

(3) 3

(4) 1

Solution: 

The correct option is (4)

P4+NaOH+H2O → PH3+NaH2PO2

NaH2PO2+ HCl → H3PO2+NaCl

Here the main product is H3PO2. In this only one hydrogen atom is attached to the oxygen and hence its basicity is one.

Question 2: The correct statement with respect to dinitrogen is

1) Liquid dinitrogen is not used in cryosurgery.

2) N2 is paramagnetic in nature

3) It can combine with dioxygen at 25oC

4) It can be used as an inert diluent for reactive chemicals.

Solution: 

(1) Liquid nitrogen is employed as a refrigerant in cryosurgery and to preserve biological material.

(2) N2 has no unpaired electrons and is diamagnetic.

(3) N2 is incompatible with oxygen, hydrogen, and the majority of other elements. However, in the presence of lightning or a spark, nitrogen will mix with oxygen.

(4) Inert diluent for reactive chemicals in the chemical industries.

Hence, the correct option is (4).

Question 3: What causes nitrogen to be chemically inert?

(a) Multiple bond formation in the molecule

(b) Absence of bond polarity

(c) Short internuclear distance

(d) High bond energy

Solution: 

Molecular nitrogen has a strong triple-bond between its atoms, making it difficult to break apart and a high amount of energy is required to do so and hence making it inert in nature. Hence the correct option is (d).

Practice Questions

Question 1: Which of the following phosphorus is most reactive?

(a) Red phosphorus 

(b) White phosphorus

(c) Scarlet phosphorus 

(d) Violet phosphorus

Answer: (b)White phosphorus

Question 2: White phosphorus on reaction with limewater gives calcium salt of an acid (A) along with a gas (X). Which of the following is correct?

(a) (A) on heating gives (X) and O2

(b) The bond angle in (X) is less than that in the case of ammonia

(c) (A) is a dibasic acid

(d) (X) is more basic than ammonia

Answer: The correct option is (b) i.e., the bond angle in (X) is less than that of ammonia

Question 3: The most non-metallic element among the following is:

(i) S

(ii) P

(iii) O

(iv) Cl

Answer: Correct option is (iv) Cl

Conclusion

Despite their differences, these nonmetals have a number of characteristics. Because they are less reactive than halogens, the majority of them may be found in nature.  They play significant biological and geochemical significance. While their physical and chemical characteristics are "moderately non-metallic," they all have corrosive properties on a net basis.