Metals And Non-Metals

Diamond is an allotrope of carbon where each carbon atom is covalently bonded to four other carbon atoms in a rigid three-dimensional network. To melt diamond, these extremely strong covalent bonds must be broken simultaneously throughout the structure, which requires a very large amount of energy. This gives diamond its exceptionally high melting point (around 3550°C or 6422°F), making it one of the hardest and highest-melting substances known.

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While physical properties (like conductivity, malleability, and lustre) provide clues, they have many exceptions (e.g., mercury is a liquid metal, graphite is a non-metal that conducts electricity). Chemical properties, specifically how an element reacts with oxygen (forming basic vs. acidic oxides) or with water/ acids, provide a more fundamental and consistent basis for classification. Metals tend to lose electrons to form positive ions and basic oxides, whereas non-metals gain electrons to form negative ions and acidic oxides.

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An amphoteric oxide is one that can react with both acids and bases to form salt and water. Aluminium oxide (Al₂O₃) demonstrates this dual behavior: it reacts with hydrochloric acid (an acid) to form aluminium chloride and water, and it also reacts with sodium hydroxide (a base) to form sodium aluminate and water. This property is characteristic of metals like aluminium, zinc, and lead.

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Alkali metals (Group 1: Li, Na, K, etc.) have only one valence electron that is loosely held, resulting in weak metallic bonding. This weak bonding causes them to have low densities (some, like lithium and sodium, even float on water) and unusually low melting points compared to other metals. For example, gallium and caesium melt on the palm of your hand.

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Due to the weak metallic bonding arising from their single valence electron, the layers of atoms in alkali metals can slide over each other with very little force. This makes them exceptionally soft. For instance, sodium and potassium can be easily cut with a regular knife, revealing a shiny, metallic surface that quickly tarnishes in air.

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Allotropy is the property of some chemical elements to exist in two or more different physical forms in the same physical state. Carbon exhibits this remarkably, with diamond (3D network), graphite (layered sheets), graphene (single atomic layer), fullerenes (cage-like molecules), and amorphous carbon (like charcoal) being its major allotropes. These differ in the arrangement of carbon atoms, leading to vastly different properties.

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The term “amphoteric” comes from the Greek word amphoteroi, meaning “both.” Amphoteric oxides act as bases when reacting with acids (neutralizing the acid to form salt and water) and as acids when reacting with bases (neutralizing the base to form salt and water). Classic examples include aluminium oxide (Al₂O₃), zinc oxide (ZnO), and lead(II) oxide (PbO).

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When magnesium burns in air, it undergoes a vigorous combination reaction with oxygen (O₂) present in the atmosphere. The chemical equation is: 2Mg(s) + O₂(g) → 2MgO(s). The white powdery ash collected after the burning is magnesium oxide. It is a basic oxide that turns red litmus blue when dissolved in water (forming magnesium hydroxide).

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Metals have a tendency to lose electrons and form positive ions (cations). When they react with oxygen, they form metal oxides. These oxides, when dissolved in water, typically form metal hydroxides, which release hydroxide ions (OH⁻) in solution, turning red litmus blue. Hence, they are classified as basic oxides. Examples: Na₂O (sodium oxide) gives NaOH; CaO (calcium oxide) gives Ca(OH)₂.

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At room temperature (25°C), most non-metals are either gases (e.g., oxygen, nitrogen, hydrogen, chlorine, fluorine) or solids (e.g., carbon, sulfur, phosphorus, iodine). Bromine is the only liquid non-metal. Oxygen, being a diatomic gas (O₂) under standard conditions, fits the description of existing in a gaseous state. Sodium is a solid metal, mercury is a liquid metal, and bromine is a liquid non-metal.

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Metals are characterized by strong metallic bonding—a “sea” of delocalized electrons surrounding positive metal ions. A large amount of energy is required to overcome this electrostatic attraction and allow the ions to move freely (melting) or escape the liquid (boiling). Therefore, most metals (e.g., iron, copper, tungsten) possess high melting points, though there are exceptions like gallium, caesium, and mercury.

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Non-metals tend to gain electrons to form negative ions (anions). Their oxides, when dissolved in water, typically form acids by releasing hydrogen ions (H₃O⁺), turning blue litmus red. For example, sulfur dioxide (SO₂) forms sulfurous acid (H₂SO₃), carbon dioxide (CO₂) forms carbonic acid (H₂CO₃), and nitrogen dioxide (NO₂) forms nitric acid (HNO₃).

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Reactivity with oxygen varies greatly among metals. Magnesium (Mg) is a highly reactive metal from Group 2. It burns vigorously in air with a dazzling white flame when heated, rapidly forming magnesium oxide. In contrast, copper reacts slowly on heating to form a black coating of copper oxide; silver and gold are noble metals that do not react with oxygen even at high temperatures.

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Graphite is an allotrope of carbon, a non-metal. Typically, non-metals are poor conductors of electricity. However, graphite has a layered structure where each carbon atom is bonded to three others, leaving one free, delocalized electron per carbon. This “sea” of delocalized electrons can move freely along the layers when a voltage is applied, making graphite an excellent conductor of electricity.

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This reaction demonstrates the amphoteric nature of aluminium oxide. When aluminium oxide (Al₂O₃) reacts with the base sodium hydroxide (NaOH), it acts as an acidic oxide. The reaction produces sodium aluminate (sodium aluminium oxide, NaAlO₂) and water. The balanced equation is: Al₂O₃(s) + 2NaOH(aq) → 2NaAlO₂(aq) + H₂O(l).

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Sodium oxide (Na₂O) is a strongly basic oxide of a highly reactive alkali metal. When it dissolves in water, it undergoes a vigorous exothermic reaction to form an alkali. The reaction is: Na₂O(s) + H₂O(l) → 2NaOH(aq). The resulting solution is sodium hydroxide, a strong base that turns red litmus blue and feels soapy to the touch.

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Among the given options, sodium is an alkali metal. Alkali metals have a very low density and extremely weak metallic bonding due to their single valence electron, making them very soft. Sodium, potassium, and lithium can all be easily cut with a simple knife, revealing a shiny, silvery surface that quickly oxidizes in air. Iron, copper, and aluminium are hard, strong metals requiring specialized tools to cut.

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At standard room temperature (25°C) and pressure, bromine (Br₂) is the only non-metal that exists as a liquid. It is a dense, reddish-brown, volatile liquid that easily evaporates to form a similarly colored, choking gas. Most other non-metals are either gases (oxygen, nitrogen) or solids (carbon, sulfur, iodine).

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Mercury (Hg) is the only metal that is liquid at standard room temperature (25°C). Its unique electron configuration (5d¹⁰6s²) results in relativistic effects that weaken the metallic bonding, preventing its atoms from being held together in a solid lattice at room temperature. While gallium and caesium have very low melting points (caesium melts at 28.5°C, gallium at 29.8°C), they are still solid at a typical room temperature of 25°C.

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Ductility is derived from the Latin ductilis, meaning “that may be led or drawn.” This mechanical property allows a metal to be stretched under tensile stress without breaking, turning it into a long, thin wire. Copper and aluminium are highly ductile, which is why they are used for electrical wiring. Malleability is the ability to be hammered into sheets, not wires.

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Thermal conductivity is highest in metals with a high density of free electrons that can rapidly transfer thermal energy. Silver (Ag) has the highest thermal conductivity of all known metals, followed very closely by copper. Although silver is the best, its high cost limits its use to specialized applications. Copper is more commonly used for cookware and heat exchangers due to its excellent conductivity and lower price.

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While all metals conduct heat better than most non-metals, there is a wide range of thermal conductivity among them. Lead (Pb) has a relatively low thermal conductivity compared to metals like silver, copper, aluminium, or iron. This is because its atomic structure and electron configuration do not allow for the same efficient transfer of thermal energy via free electrons. This property makes lead useful for shielding and soldering.

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Malleability (from Latin malleus, meaning “hammer”) is the property of a material to deform under compressive stress (e.g., hammering or rolling) without breaking, allowing it to be formed into thin sheets. Gold is the most malleable metal; a single gram can be beaten into a sheet of one square meter. Ductility refers to drawing into wires, not sheets.

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Sonority is the property of metals to produce a deep, resonant, ringing sound when struck. This occurs because when a metal object is hit, the free electrons in the metallic lattice can move and quickly distribute the vibrational energy throughout the structure, producing a sustained tone. Non-metals, lacking free-moving electrons, are typically non-sonorous and produce a dull, thudding sound when struck.

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Potassium oxide (K₂O) is a basic oxide of an alkali metal. Similar to sodium oxide, it reacts violently with water to form a strong alkali. The reaction is: K₂O(s) + H₂O(l) → 2KOH(aq). The resulting solution is potassium hydroxide, a strong base used in the manufacture of soaps and detergents. The solution turns red litmus paper blue.

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When sulfur (a non-metal) burns in air, it combines with oxygen to form sulfur dioxide (SO₂). The balanced equation is: S(s) + O₂(g) → SO₂(g). Sulfur dioxide is an acidic oxide. When dissolved in water, it forms sulfurous acid (H₂SO₃), which donates H⁺ ions, turning blue litmus red and demonstrating its acidic nature.

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As explained previously, graphite’s unique structure—each carbon atom bonded to three others in parallel layers—leaves one free, delocalized electron per carbon atom. These delocalized electrons can move freely along the planes when an electric field is applied, making graphite a good conductor. Diamond, with all four electrons used in strong covalent bonds, is an electrical insulator. Charcoal and coal are poor conductors.

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The direct combination of a metal with oxygen is a type of oxidation reaction or combustion. The general equation is: Metal + Oxygen → Metal Oxide. For example, 2Mg + O₂ → 2MgO; 4Al + 3O₂ → 2Al₂O₃; 2Cu + O₂ → 2CuO. While these metal oxides may react further with water to form bases (hydroxides), the primary product of the reaction with oxygen alone is the metal oxide.

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Magnesium oxide (MgO) is a basic metal oxide. When it dissolves in water, it reacts chemically to form magnesium hydroxide: MgO(s) + H₂O(l) → Mg(OH)₂(aq). Magnesium hydroxide dissociates slightly to release OH⁻ ions, making the solution alkaline (basic). This is verified by the solution turning red litmus paper blue.

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An alkali is a base that is soluble in water. Most metal oxides are bases, but only the oxides of Group 1 (alkali metals) and Group 2 (alkaline earth metals, except Be) are soluble in water. Sodium oxide (Na₂O) is highly soluble and reacts vigorously to form sodium hydroxide (NaOH), a strong alkali. Copper(II) oxide (CuO), iron(III) oxide (Fe₂O₃), and zinc oxide (ZnO) are bases but are insoluble in water.

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This shows the basic nature of amphoteric aluminium oxide. When acting as a base, it neutralizes acids to form a salt and water. The general reaction is: Metal oxide + Acid → Salt + Water. A specific example is: Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(l). Therefore, with hydrochloric acid, it forms aluminium chloride and water. The salt formed depends on the acid used.

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The normal temperature of the human palm is about 36-37°C. Gallium melts at 29.8°C and caesium at 28.5°C. Both are well below body temperature. When you hold a piece of these metals in your hand, the heat transferred from your palm provides enough energy to overcome their extremely weak metallic bonds, causing them to change from solid to liquid.

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Sonority is the specific property of metals that allows them to produce a ringing sound when struck. This is a physical property distinct from conductivity, malleability, or ductility. The delocalized electrons in the metallic lattice enable the efficient transmission of vibrational waves, leading to the characteristic sound of a bell or a coin being dropped.

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The vast majority of metals are solid at room temperature (25°C). Mercury (Hg) is the only stable metallic element that is liquid at this temperature. This exceptional state arises from relativistic effects in its electron cloud that contract the 6s orbital, making the 6s electrons very tightly bound and unavailable for metallic bonding, thus preventing the formation of a stable solid lattice at room temperature.

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Metallic lustre is the characteristic shine exhibited by most metals on a clean, freshly cut surface. This occurs because the delocalized, free electrons on the metal surface absorb photons of light and then re-emit them across a wide range of frequencies. This property makes metals opaque and reflective. The lustre can be lost due to oxidation or tarnishing (e.g., silver tarnishes to black).

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Classifying elements solely on physical properties like state (solid/liquid/gas), conductivity, or appearance leads to inconsistencies. For example, mercury is a liquid metal (exception to “metals are solids”). Graphite is a non-metal that conducts electricity (exception to “non-metals are poor conductors”). Iodine is a non-metal that is lustrous. Because of these many exceptions, chemical properties provide a more reliable classification.

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Blue litmus paper is used to test for acidic conditions. When sulfur dioxide (SO₂), an acidic oxide, dissolves in water, it forms sulfurous acid (H₂SO₃). This acid releases H⁺ ions into the solution, which react with the blue litmus dye, turning it red. This confirms the acidic nature of the solution formed by dissolving SO₂.

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Sonority (the ability to produce a ringing sound when struck) is a characteristic property of metals. Non-metals lack the free-moving electrons needed to transmit vibrational energy efficiently. When struck, non-metals like sulfur, carbon (in diamond form), or iodine are typically brittle and produce a dull, non-ringing sound, hence they are described as non-sonorous.

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When copper metal is heated in air, it reacts with oxygen to form copper(II) oxide. The equation is: 2Cu(s) + O₂(g) → 2CuO(s). Copper(II) oxide is a black solid. Zinc forms zinc oxide (white), iron forms a complex black/brown magnetic oxide (Fe₃O₄) but is often seen as rust (red-brown), and aluminium forms aluminium oxide (white or transparent).

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Cooking vessels need to efficiently transfer heat from the stove burner to the food. Metals are excellent thermal conductors, meaning they allow heat energy to flow quickly and evenly through their structure. This property, thermal conductivity (specifically the high density of free electrons transferring kinetic energy), makes materials like copper, aluminium, and stainless steel ideal for pots and pans.

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This is a direct combination reaction known as oxidation or combustion. When a metal combines chemically with the oxygen present in air, especially on heating, the product is a metal oxide. Examples: 2Mg + O₂ → 2MgO; 4Al + 3O₂ → 2Al₂O₃; 2Fe + O₂ → 2FeO. The other options represent different types of reactions (e.g., metal with acid produces salt + hydrogen).

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Lustre (shininess) is typically a metallic property, but there are exceptions. Iodine is a non-metal that forms dark grey, crystalline solid that possesses a distinct metallic lustre. This is due to the way its layered molecular crystal structure interacts with light. While diamond (a form of carbon) is lustrous, amorphous carbon (like charcoal) is not. Among the given options, iodine is the correct example.

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Diamond’s extreme hardness is a direct result of its three-dimensional network covalent structure. Each carbon atom is bonded to four others with strong, directional covalent bonds, forming a rigid, interlocking framework with no weak planes. This makes diamond extremely resistant to scratching or deformation, giving it the highest hardness rating (10 on the Mohs scale) of any natural mineral.

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The speed and vigor of a metal’s reaction with oxygen are determined by its inherent chemical reactivity. This is summarized in the reactivity series of metals. Highly reactive metals like potassium and sodium react violently with oxygen even at room temperature. Moderately reactive metals like magnesium and aluminium react quickly when heated. Noble metals like gold and platinum have very low reactivity and do not react with oxygen at all.

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Non-metals typically lack a supply of free, delocalized electrons. Their valence electrons are tightly held in covalent bonds within individual molecules or atomic networks. Without mobile charge carriers (electrons or holes), non-metals cannot efficiently conduct electricity or heat. Graphite is a notable exception due to its delocalized electrons, but the general property of non-metals is poor conductivity.

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Both thermal and electrical conductivity in metals originate from the same source: the presence of a “sea” of delocalized, free-moving valence electrons. An applied electric field causes these electrons to drift, creating an electric current. An applied temperature gradient causes the electrons to transfer kinetic energy from the hot end to the cold end, conducting heat. Hence, good electrical conductors are also good thermal conductors.

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When heated to its ignition temperature, magnesium reacts extremely exothermically with oxygen. The energy released is so intense that it produces a brilliant, dazzling white light (often described as blinding). This light is rich in ultraviolet radiation as well as visible light. This property was historically used in photographic flashbulbs and is used today in fireworks and incendiary devices.

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This again tests the concept of amphoteric oxides. Aluminium oxide (Al₂O₃) reacts with both acids (showing basic nature) and bases (showing acidic nature). Magnesium oxide (MgO) is purely basic. Carbon dioxide (CO₂) is purely acidic. Sodium oxide (Na₂O) is strongly basic. Only Al₂O₃ among the options exhibits this dual, amphoteric behavior.

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In their pure, untarnished state, most metals possess a characteristic shine known as metallic lustre. This is because their smooth surfaces are able to reflect a broad spectrum of light. While some metals may appear dull due to oxidation (a layer of metal oxide forming on the surface), scratching or cutting the metal reveals the lustrous surface underneath. The general, defining property is lustre.

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The “ash” is magnesium oxide (MgO), a basic oxide. When dissolved in water, it forms magnesium hydroxide (Mg(OH)₂). Red litmus paper is used to test for bases. When an alkali (like Mg(OH)₂ solution) comes into contact with red litmus, it turns the dye blue. This demonstrates the basic nature of the magnesium oxide formed during combustion.Close