Metals


  metal metals
The greater part of elements in the Periodic Table is metals. Metals vary from the extremely reactive alkali metals like sodium to inert metals like gold.

Metals have common physical properties but variable chemical properties.

The physical properties of metals are:

• Metals are glossy, solid and good conductors of heat and electricity.

• Metals have high density.

• They are malleable and ductile, deforming under strain without cutting.

• Metals are shiny and lustrous.

Sheets of metal below a few micrometers in breadth have opaque appearance apart from Gold leaf which gives off green light.

Even though majority of metals have lofty densities than nearly all nonmetals, they have broad variation in their densities, with Lithium being the slightest dense solid element and osmium the densest.

The alkali and alkaline earth metals in groups I A and II A are known as the light metals for the reason that they have small density, less hard and low melting points. The lofty density of the majority of metals is due to the firmly packed crystal lattice of the metallic structure. The strength of metallic bonds for dissimilar metals reaches the utmost around the center of the transition metal series, since those elements have huge amounts of delocalized electrons in tight binding form of metallic bonds. Nevertheless, other factors like atomic radius, nuclear charge, amount of bonds orbital’s’ overlap of orbital energies and crystal form are also involved.

Chemical properties of metals

• Metals have the tendency to form cations through loss of electron.

• They react with oxygen in the air to form oxides. This explains why metals like iron rust when they are exposed over a long period of time and why potassium instantly burns in the presence of oxygen in the atmospheric air.

• For Example: Sodium, calcium and aluminum reacts with air to for their oxides respectively as exemplified in the equations below:

4 Na + O2 → 2 Na2O (sodium oxide)

2 Ca + O2 → 2 CaO (calcium oxide)

4 Al + 3 O2 → 2 Al2O3 (aluminum oxide)

The transition metals like iron, copper, zinc, and nickel are less reactive. They don’t easily react with oxygen in the air due to the fact that they form passive layer of oxide that shields the core. Other metals like palladium, platinum and gold, are completely not reactive with air. Some metals form a barricade layer of oxide on their surface which could hardly be pierced by extra molecule of oxygen. In so doing, they maintain their lustrous appearance and continue to be good conductors of electricity for ages. Examples are aluminum, magnesium, various steels, and titanium

Metallic oxides are characteristically basic in nature contrary to the oxides of non-metals which are normally acidic in nature. Obvious exceptions are mainly oxides of metal with especially high oxidation states like that of CrO3, Mn2O7, and OsO4, which have severely acidic reactions.

Prevention of rusting or corrosion of metals

Metals can be protected to prevent them rusting when exposed to atmospheric air through the following procedures Painting, anodizing or plating of metals. Although, a metal that is more reactive in the electrochemical series must be used for coating particularly when chipping of the coating is anticipated. Water and the two metals form an electrochemical cell. If the metal used for coating is less reactive than the coated metal, the coating will in fact encourage corrosion.

Corrosion of metals

Metals have many useful physical properties

• The strength of metals is useful in girders

• The reflective power of metal is useful in headlamps

• The electrical conductivity of metals is useful in making electrical cables

•Metals are stable to heat and this characteristics is useful in engines

Metals higher up in the series will displace those further down the series

Zn (metal) + Cu2+ + → Cu (metal) + Zn2+

This type of reaction is known as redox reactions.

Metallic Structure and bonding:

The atoms of metals are packed closely to adjoining 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 second arrangement is referred to as face-centered cubic. In this second arrangement, every atom is placed at the middle of the other six. This leads to the formation of a crystal. A few metals have variable shape depending on the temperature condition.

Metallic atoms easily give out their valence electrons, leading to the formation of free flowing cloud of electrons within their solid arrangement. This is why metals have the ability to readily conduct heat and electricity. As there are free movements of these electrons, the metallic structure are kept intact by the electrostatic interactions between every atom and the electron cloud. This is what is normally known as metallic bond.

Electrical and thermal conductivities of metals

Electrical

The electrical and thermal conductivities of metals started off from the reality that their external electrons are delocalized. This circumstance can be seen through the atomic structure of a metal as a compilation of atoms implanted in a sea of extremely mobile electrons. The electrical conductivity, together with the electrons’ contribution to the heat power and heat conductivity of metals can be considered and estimated through the free electron model, which does not take into consideration the comprehensive arrangement of the ion lattice.

Mechanical Properties of metal

Mechanical properties of metals are:

• Ductility- This is their aptitude for plastic deformation.

Reversible elastic deformation in metals can be explained through Hooke’s Law for reinstating forces, where the stress is directly proportional to the strain. Forces applied in excess of the elastic limit or heat may lead to irreversible deformation of the object. This phenomenon is known as plastic deformation or plasticity. This irreversible change in atomic arrangement may occur as a result of:

• The action of an applied force which can be tensile (pulling) force, compressive (pushing) force, cut off, twisting or torsion (twisting) forces.

• An alteration in temperature (heat) which may alter the movement of the structural defects.

Alloys

An alloy is a mixture of two or more elements in which the major component is a metal. The majority of pure metals are either too soft, brittle or chemically reactive for realistic use. Combination of various ratios of metals as alloys adjusts the properties of pure metals to manufacture enviable characteristics. The major reason for forming alloys is to make the metals less brittle, harder, anti corrosive, or enclose a more attractive color and luster.

Among the current available alloys, the alloys of iron, steel, stainless steel, cast iron, tool steel and alloy steel constitute the principal percentage both by magnitude and commercial value. Iron that is alloyed with a variety of proportions of carbon yields low, mid and high carbon steels, with escalating carbon levels lowering ductility and toughness. The adding together of silicon will give rise to cast irons, while addition of chromium, nickel and molybdenum to carbon steels in a quantity over 10% will give rise to stainless steels.

Other noteworthy metallic alloys are alloys of aluminum, titanium, copper and magnesium. Copper alloys have been discovered early in history.

Bronze was what gave the Bronze Age its name. It is used for many things today especially in electrical wiring. The alloys of additional three metals have been developed quite lately; for the fact of their chemical reactivity they need electrolytic extraction processes. The alloys of aluminum, titanium and magnesium are prized for their lofty strength/weight ratios; magnesium can also offer electromagnetic shielding. These materials are perfect for situations where elevated strength/weight ratio is more crucial than the cost of the material like in aerospace and a number of automotive applications.

Alloys are especially designed for extremely challenging applications, like jet engines and may include more than ten elements.

Base metal

The term base metal is used in Chemistry to refer to a metal that oxidizes or corrodes rather simply, and reacts variably with dilute hydrochloric acid (HCl) to form hydrogen. Examples of base metals are iron, nickel, lead and zinc. Copper is also well thought-out to be among base metals as it oxidizes rather readily, even though it does not act in response with HCl. It is generally used contrary to noble metal.

A base metal was a widespread and low-priced metal, contrary to precious metals, like gold and silver. The purpose of work of the alchemists was the transformation of base metals into precious metals.

Ferrous metal

Ferrous and non-ferrous metals

Ferrous metals are metals that contain iron. The expression “ferrous” is derived from a Latin word. Ferrous means “containing iron”. The iron may be pure iron like wrought iron, or an alloy like steel. Ferrous metals are frequently magnetic, but not completely.

Noble metal

Noble metals are metals that doesn’t corrode or oxidize as opposed to most base metals. They are inclined to be valuable metals, frequently due to apparent rarity for instance, gold, platinum, silver and rhodium.

The Reactivity Series of metals

The activity series of metals is an empirical instrument used to foresee products in displacement reactions and reactivity of metals with (H20) water and acids in replacement reactions and ore extraction. It can be employed to foretell the products in related reactions connecting dissimilar metal.

The activity series is a chart of metals written in descending order of their relative reactivity. The metals on top of the series are more reactive than the metals on the foot. For instance, both magnesium and zinc can react with hydrogen ions to displace H2 from a solution by the reactions below:

Mg(s) + 2 H+(aq) → H2 (g) + Mg2+ (aq)

Zn(s) + 2 H+(aq) → H2(g) + Zn2+(aq)

The two metals react with the hydrogen ions, but magnesium metal can as well displace zinc ions in solution by the reaction below:

Mg(s) + Zn2+ → Zn(s) + Mg2+

This signifies that magnesium is additionally reactive than zinc and that the two metals are more reactive than hydrogen.

By comparing the reactions of metals in oxygen, water and acid, metal oxides and solutions of metal salts, we can organize metals into a list of reactivity known as the Reactivity Series. The more reactive a metal is the more able it is to form a compound. Again, the more reactive a metal, the more stable its compound.

Furthermore, the more reactive a metal, the more difficult it is to extract from its compounds.

Copper, silver and gold exist as elements in the earth because they are un reactive in nature. They are easy to extract.

Reactive metals are additionally difficult to extract. They are frequently discovered as compounds or ores.

A method of extraction known as Electrolysis is used to eliminate the element from the rest of the compound.

Extraction of Metals

Metals are habitually extracted from the Earth through the process of mining, leading to ores that are reasonably rich sources of the essential elements.

Immediately the ore is mined, the metals need to be extracted, usually through the use of a chemical or through electrolysis.

The extraction method to be used depends on the metal and their impurity.

When a metallic ore is present in an ionic compound of the metal and a non-metal, the ore have got to be smelted. This means heating it up with a reducing agent to extract the pure metal.

The majority of ordinary metals, like iron, are smelted with carbon as a reducing agent. Some metals, like aluminum and sodium, have no reducing agent that is commercially sensible. Because of this, they are extracted through the process of electrolysis. Sulfide ores are not reduced straight to the metal but are burnt in air to convert them to oxides.

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