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Metals and Non-Metals - Part I |
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There
are about 90 elements, up to Uranium, that are found naturally. Another 20
elements, beyond Uranium, called trans-uranium elements, have been produced
artificially in the laboratories by nuclear reactions. Two elements, Technetium
(Tc) and Promethium (Pm) that occur below Uranium are unstable in
nature. Elements can be classified by the physical and chemical properties
that they display. We have discussed about classification of elements in
earlier chapters. The
chemical behavior of all elements depends on their electronic
configurations. It is the electrons that take part in chemical reactions and
therefore their interactions are the main factors that determine the outcome
of a chemical reaction. The periodic table of elements
has been made on the basis of electronic configuration of elements alone. Depending
on the availability of “free” electrons, elements can be classified as
metals and non-metals. Free electrons are unbound electrons, beyond closed
shells. In metals, these
unbound electrons are given off or donated during compound formation. In
non-metals, there are no free electrons, instead there is a deficiency of
electrons. While forming compounds, non-metals borrow electrons. Examples of
metals are Sodium (Na), Potassium (K), Gold (Au). Examples of non-metals are
Carbon (C ), Oxygen (O), Nitrogen (N), Chlorine (Cl).
Metals are shown on the left-hand side and centre of the periodic
table. Non-metals are placed on the right hand side of the periodic table. Chemically inert gases like Helium (He), Neon
(Ne), Argon (Ar),
Krypton (Kr) and Xenon (Xe) are included in the category of non-metals. Some
elements placed in between the metals and non-metals in the periodic table
are called metalloids. Metalloids behave either like metals or like
non-metals; their behavior depends on the environment that they are placed
into. Metalloids are few in number. Examples of metalloids are Arsenic (As),
Antimony (Sb), Germanium (Ge), etc. Thus metalloids form a bridge between
strictly metal elements and strictly non-metal elements. What
we will study in this chapter
: 1.
Electronic
configuration of metals and non-metals Table
below gives electronic configuration of some metals.
Table
below gives electronic configuration of some non-metals.
It
is clear from these tables that to complete a given orbit, metals give off
electrons and become positive ions. Non-metals accept electrons and become
negative ions. Hydrogen (H) and
Helium (He) are two light elements which are non-metallic in nature.
Hydrogen lacks one electron to complete its one and only one shell. Helium
has 2 electrons in its only orbit[1].
As discussed earlier in the chapter on Classification of Elements, the periodic table of elements has classified elements in different groups and periods. The groups and periods are made according to the electronic configuration of elements. The metals are placed on the left side and the centre of the periodic table. The non-metals are placed on the right side of the periodic table. Hydrogen is the only non-metal that is placed on the left-hand side of the periodic table. The reason for this is that the electronic configuration of H is 1s1, same as the Group I A elements or the alkali elements such as Na, and K. The middle portion of the periodic table consists of elements that are called transition metals elements. These elements are metallic in nature but not as metallic as alkali (Na, K, Cs etc) or alkaline earth metals (Mg, Ca etc.) [1] Although H and He are taken as non-metals, these elements show metallic properties at ultra low temperatures (close to absolute zero or 0 K).
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