METAL

METAL

                A metal (from Greek "μέταλλον" – métallon, "mine, quarry, metal"[1][2]) is a material (an element, compound, or alloy) that is typically hard, opaque, shiny, and features good electrical and thermal conductivity. Metals are generally malleable — that is, they can be hammered or pressed permanently out of shape without breaking or cracking — as well as fusible (able to be fused or melted) and ductile (able to be drawn out into a thin wire).[3] About 91 of the 118 elements in the periodic table are metals (some elements appear in both metallic and non-metallic forms).

                The atoms of metallic substances are closely positioned to neighboring atoms in one of two common arrangements. The first arrangement is known as body-centered cubic. In this arrangement, each atom is positioned at the center of eight others. The other is known as face-centered cubic. In this arrangement, each atom is positioned in the center of six others. The ongoing arrangement of atoms in these structures forms a crystal. Some metals adopt both structures depending on the temperature.

                Metals are usually inclined to form cations through electron loss,[6] reacting with oxygen in the air to form oxides over various timescales (iron rusts over years, while potassium burns in seconds). Metals in general have high electrical conductivity, high thermal conductivity, and high density. Typically they are malleable and ductile, deforming under stress without cleaving.[6] In terms of optical properties, metals are shiny and lustrous. Sheets of metal beyond a few micrometres in thickness appear opaque, but gold leaf transmits green light.Although most metals have higher densities than most nonmetals,[6] there is wide variation in their densities.

                The electrical and thermal conductivities of metals originate from the fact that their outer electrons are delocalized. This situation can be visualized by seeing the atomic structure of a metal as a collection of atoms embedded in a sea of highly mobile electrons. The electrical conductivity, as well as the electrons' contribution to the heat capacity and heat conductivity of metals can be calculated from the free electron model, which does not take into account the detailed structure of the ion lattice.

                Mechanical properties of metals include ductility, i.e. their capacity for plastic deformation. Reversible elastic deformation in metals can be described by Hooke's Law for restoring forces, where the stress is linearly proportional to the strain. Forces larger than the elastic limit, or heat, may cause a permanent (irreversible) deformation of the object, known as plastic deformation or plasticity. An alloy is a mixture of two or more elements in which the main component is a metal. Most pure metals are either too soft, brittle or chemically reactive for practical use. Combining different ratios of metals as alloys modifies the properties of pure metals to produce desirable characteristics.Metals are often extracted from the Earth by means of mining, resulting in ores that are relatively rich sources of the requisite elements.

NONMETAL

                In chemistry, a nonmetal or non-metal is a chemical element that mostly lacks metallic attributes. Physically, nonmetals tend to be highly volatile (easily vaporised), have low elasticity, and are good insulators of heat and electricity; chemically, they tend to have high ionisation energy and electronegativity values, and gain or share electrons when they react with other elements or compounds. Seventeen elements are generally classified as nonmetals; most are gases (hydrogen, helium, nitrogen, oxygen, fluorine, neon, chlorine, argon, krypton, xenon and radon); one is a liquid (bromine); and a few are solids (carbon, phosphorus, sulfur, selenium, and iodine).

                There is no rigorous definition of a nonmetal. They show more variability in their properties than do metals.[8] The following are some of the chief characteristics of nonmetals.[9] Physically, they largely exist as monatomic gases, with a few having more substantial (but still open-packed) diatomic or polyatomic forms, unlike metals which are nearly all solid and close-packed; if solid, they generally have a submetallic or dull appearance and are brittle, as opposed to metals, which are lustrous, ductile or malleable; they usually have lower densities than metals; are poor conductors of heat and electricity when compared to metals; and have significantly lower melting points and boiling points than those of metals (with the exception of carbon). Chemically, the nonmetals have relatively high ionisation energy and high electronegativity; they usually exist as anions or oxyanions in aqueous solution; generally form ionic or interstitial compounds when mixed with metals, unlike metals which form alloys; and have acidic oxides whereas the common oxides of the metals are basic.

                Nonmetals have structures in which each atom usually forms (8 − N) bonds with (8 − N) nearest neighbours, where N is the number of valence electrons. Each atom is thereby able to complete its valence shell and attain a stable noble gas configuration. Exceptions to the (8 − N) rule occur with hydrogen (which only needs one bond to complete its valence shell), carbon, nitrogen and oxygen. Atoms of the latter three elements are sufficiently small such that they are able to form alternative (more stable) bonding structures, with fewer nearest neighbours.Nonmetals do not have any universal or near-universal applications. This is not the case with metals, most of which have structural uses; nor the metalloids, the typical uses of which extend to (for example) oxide glasses, alloying components, and semiconductors.

DIFFERENCE

Metals and non-metals differ tremendously in their physical and chemical characteristics. On the periodic table, the metals are separated from nonmetals by a zigzag line which passes through carbon, phosphorus, selenium, iodine and radon. These elements and those to the right of them are nonmetals. The elements just to the left of the line are metalloids or semimetals. Metalloids have properties similar to both metals and non-metals. The elements left of the metalloids are metals.

The distinguishing properties of metals and non-metals are listed below.

Metals

Physical Properties

Usually solid when in room temperature except mercury, which is liquid

Have a lustrous or shiny look

Are good conductors of heat and electricity

Have a high melting and boiling point

Have a high density, are heavy for their size

Are malleable, i.e. can be hammered into sheets

Are ductile, i.e. can be drawn into wires

Are opaque as a thin sheet

Are sonorous, i.e. make a bell-like sound when struck

Chemical Properties

Have 1-3 electrons in the outer shell of each metal atom

Corrode easily, i.e. damaged by oxidation such as tarnish or rust

They lose electrons easily

They form oxides that are basic in nature

Have lower electro-negativities

Are good reducing agents

Non-metals

Nonmetals include carbon, hydrogen, nitrogen, phosphorous, oxygen, sulfur, selenium, halogens and the noble gases.

Physical Properties

Are not lustrous, have a dull appearance

Are poor conductors of heat and electricity

Are non-ductile solids

Are brittle solids

May be solids, liquids or gases at room temperature

Are transparent as a thin sheet

Are not sonorous, i.e. do not make a bell-like sound when struck

 Chemical Properties

Usually have 4-8 electrons in their outer shell

They readily gain or share valence electrons

They form oxides that are acidic in nature

They have higher electro-negativities

Are good oxidizing agents