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Monday, 26 March 2012

Periodic Table: Pictorial Journey of Metals :Part 2

The Alkali metals:
 Are a group of chemical elements in the periodic table with very similar properties: they are all shiny, soft, silvery, highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1.[2]:28 They can all be cut easily with a knife due to their softness, exposing a shiny surface that tarnishes rapidly in air due to oxidation. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements excluding hydrogen (H), which is nominally a group 1 element but not normally considered to be an alkali metal as it rarely exhibits behaviour comparable to that of the alkali metals.

The alkali metals are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). This group lies in the s-block of the periodic table[citation needed] as all alkali metals have their outermost electron in an s-orbital. The alkali metals provide the best example of group trends in properties in the periodic table,with elements exhibiting well-characterized homologous behaviour.

All the discovered alkali metals occur in nature.Experiments have been conducted to attempt the synthesis of ununennium (Uue), which is likely to be the next member of the group, but they have all met with failure.However, ununennium may not be an alkali metal due to relativistic effects, which are predicted to have a large influence on the chemical properties of superheavy elements.
Most alkali metals have many different applications. Two of the most well-known applications of the pure elements are rubidium and caesium atomic clocks,of which caesium atomic clocks are the most accurate representation of time known as of 2012. A common application of the compounds of sodium is the sodium vapour lamp, which emits very efficient light. Table salt, or sodium chloride, has been used since antiquity.


The Alkaline earth metals: 
Are a group in the periodic table. In the modern IUPAC nomenclature, the alkaline earth metals are called the group 2 elements. Previously, they were called the Group IIA elements (pronounced "group two A", as the "II" here is a Roman numeral). The alkaline earth metals contain beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). (Although helium (He) is occasionally considered to be a group 2 element, e.g. in the extended periodic table and Janet periodic table, it never exhibits behaviour comparable to the alkaline earth metals.) The group lies in the s-block of the periodic table.
This specific group in the periodic table owes its name to their oxides that simply give basic alkaline solutions. These oxides melt at such high temperature that they remain solids ("earths") in fires. The alkaline earth metals provide a good example of group trends in properties in the periodic table, with well-characterized homologous behavior down the group. With the exception of beryllium and magnesium, the metals have a distinguishable flame color, orange for calcium, bright red for strontium, green for barium and crimson red for radium.

All of the alkaline earth metals discovered, as of 2012, are naturally occurring (see references in abundance of the chemical elements), and share similar properties: they are all rather reactive metals under standard conditions. So far, experiments have been conducted to attempt the synthesis of the next member of the group, unbinilium (Ubn), but these have all met with failure. However, since unbinilium is the second period 8 element and only the second element on the periodic table that has not been discovered yet, it is likely to be discovered in the near future.


Noble gas:

The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity. The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn).
For the first six periods of the periodic table, the noble gases are exactly the members of group 18 of the periodic table. However, this may no longer hold in the seventh period (due to relativistic effects); the next member of group 18 after radon, ununoctium, is probably not a noble gas. Instead, group 14 member ununquadium likely exhibits noble-gas-like properties.
The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence electrons is considered to be "full", giving them little tendency to participate in chemical reactions, and it has only been possible to prepare a few hundred noble gas compounds. The melting and boiling points for each noble gas are close together, differing by less than 10 °C (18 °F); consequently, they are liquids over only a small temperature range.

Neon, argon, krypton, and xenon are obtained from air using the methods of liquefaction of gases and fractional distillation. Helium is typically separated from natural gas, and radon is usually isolated from the radioactive decay of dissolved radium compounds. Noble gases have several important applications in industries such as lighting, welding, and space exploration. A helium-oxygen breathing gas is often used by deep-sea divers at depths of seawater over 55 m (180 ft) to keep the diver from experiencing oxygen toxemia, the lethal effect of high-pressure oxygen, and nitrogen narcosis, the distracting narcotic effect of the nitrogen in air beyond this partial-pressure threshold. After the risks caused by the flammability of hydrogen became apparent, it was replaced with helium in blimps and balloons.


Nonmetal, or non-metal:
Is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, every element in the periodic table can be termed either a metal or a nonmetal. (A few elements with intermediate properties are referred to as metalloids).
The elements generally regarded as nonmetals are:

In Group 14: carbon (C)
In Group 15 (the pnictogens): nitrogen (N), phosphorus (P)
In Group 16 (the chalcogens): oxygen (O), sulfur (S), selenium (Se)
All elements (with the possible exception of ununseptium) in Group 17 - the halogens
All elements (with the possible exception of ununoctium) in Group 18 - the noble gases

There is no rigorous definition for the term "nonmetal" - it covers a general spectrum of behaviour. Common properties considered characteristic of a nonmetal include:
poor conductors of heat and electricity when compared to metals
they form acidic oxides (whereas metals generally form basic oxides)
in solid form, they are dull and brittle, rather than metals which are lustrous, ductile or malleable
usually have lower densities than metals
they have significantly lower melting points and boiling points than metals (with the exception of carbon)
non-metals have high electronegativity
Only eighteen elements in the periodic table are generally considered nonmetals, compared to over eighty metals, but nonmetals make up most of the crust, atmosphere and oceans of the earth. Bulk tissues of living organisms are composed almost entirely of nonmetals. Most nonmetals are monatomic noble gases or form diatomic molecules in their elemental state, unlike metals which (in their elemental state) do not form molecules at all.


Poor metals:
The trivial name poor metals is sometimes applied to the metallic elements in the p-block of the periodic table. Their melting and boiling points are generally lower than that of the transition metals and their electronegativity higher, and they are also softer. They are distinguished from the metalloids by their significantly higher boiling points and conductivity in the same period.

"Poor metals" is not a rigorous IUPAC-approved nomenclature, but the grouping is generally taken to include aluminium, gallium, indium, tin, thallium, lead and bismuth. Occasionally germanium, antimony and polonium are also included, although these are usually considered to be metalloids or "semi-metals". Elements 113, 114, 115, and 116, which are currently allocated the systematic names ununtrium, ununquadium, ununpentium, and ununhexium, would likely exhibit properties characteristic of poor metals; sufficient quantities of them have not yet been synthesized to examine their chemical properties


Precious Semi metals:
A precious metal is a rare, naturally occurring metallic chemical element of high economic value. Chemically, the precious metals are less reactive than most elements, have high lustre, are softer or more ductile, and have higher melting points than other metals. Historically, precious metals were important as currency but are now regarded mainly as investment and industrial commodities. Gold, silver, platinum, and palladium each have an ISO 4217 currency code.
The best-known precious metals are the coinage metals gold and silver. While both have industrial uses, they are better known for their uses in art, jewellery and coinage. Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum is the most widely traded.

Assortment of precious metals
The demand for precious metals is driven not only by their practical use but also by their role as investments and a store of value. Historically, precious metals have commanded much higher prices than common industrial metals


Transition Metal:
In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings:
The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell".

Most scientists describe a "transition metal" as any element in the d-block of the periodic table, which includes groups 3 to 12 on the periodic table. All elements in the d-block are metals. In actual practice, the f-block is also included in the form of the lanthanide and actinide series.

Jensen has reviewed the history of the terms transition element (or metal) and d-block. The word transition was first used to describe the elements now known as the d-block by the English chemist Charles Bury in 1921, who referred to a transition series of elements during the change of an inner layer of electrons (for example n=3 in the 4th row of the periodic table) from a stable group of 8 to one of 18, or from 18 to 32.

With a few minor exceptions, the electronic structure of transition metal atoms can be written as [ ]ns2(n-1)dm, where the inner d orbital has more energy than the valence-shell s orbital. In divalent and trivalent ions of the transition metals, the situation is reversed such that the s electrons have higher energy. Consequently, an ion such as Fe2+ has no s electrons: it has the electronic configuration [Ar]3d6 as compared with the configuration of the atom, [Ar]4s23d6.

The elements of groups 4–11 are now generally recognized as transition metals, as are Sc and Y in Group 3. For the elements La-Lu and Ac-Lr and also for Group 12, different sets of definitions are used by different authors.


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