Alkali metal

The alkali metals are a group (column) in the periodic table consisting of the chemical elements lithium (Li), sodium (Na), potassium (K),rubidium (Rb), caesium (Cs), and francium (Fr). This group lies in the s-block of the periodic table of elements as all alkali metals have their outermost electron in an s-orbital: this element/electron configuration results in their characteristic properties. The alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterized homologous behaviour.

The alkali metals have very similar properties: they are all shiny, soft, highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1. 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 by atmospheric moisture and oxygen. Because of their high reactivity, they must be stored under oil to prevent reaction with air, and are found naturally only in salts and never as the free element. 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. All the alkali metals react with water, with the heavier alkali metals reacting more vigorously than the lighter ones.

Indian Institute of Technology Joint Entrance Examination

The Indian Institutes of Technology Joint Entrance Examination (IIT-JEE) was an annual engineering college entrance examination in India. It was used as the sole admission test by the 16 Indian Institutes of Technology (IITs) and Indian School of Mines Dhanbad (to be converted into IIT). The examination was organised each year by one of the various IITs, on a round robin rotation pattern. It had a very low admission rate (about 10,000 in 500,000 in 2011), and was thus recognised as one of the toughest examinations in the world.

In 2013 it was replaced by the two-phase Joint Entrance Examination.

History

The first IIT, IIT Kharagpur, started in 1951. In the initial few years (1951-1954) students were admitted on the basis of their academic results followed by an Interview in several Centers across the country. From 1955-1959 admission was via an all India examination held only for IIT Kharagpur (other IITs had not started by then). Branches were allotted through Interviews/counselling held at Kharagpur.

Atomic mass

The atomic mass (m_a) is the mass of an atomic particle, sub-atomic particle, or molecule. It is commonly expressed in unified atomic mass units (u) where by international agreement, 1 unified atomic mass unit is defined as 1/12 of the mass of a single carbon-12 atom (at rest). For atoms, the protons and neutrons of the nucleus account for almost all of the mass, and the atomic mass measured in u has nearly the same value as the mass number.

When divided by unified atomic mass units or daltons to form a pure number ratio, the atomic mass of an atom becomes a dimensionless number called the relative isotopic mass (see section below). Thus, the atomic mass of a carbon-12 atom is 12 u or 12 daltons (Da), but the relative isotopic mass of a carbon-12 atom is simply 12.

Periodic table

The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number (number of protons), electron configurations, and recurring chemical properties. This ordering shows periodic trends, such as elements with similar behavior in the same column. It also shows four rectangular blocks with some approximately similar chemical properties. In general, within one row (period) the elements are metals on the lefthand side, and non-metals on the righthand side.

The rows of the table are called periods; the columns are called groups. Six groups (columns) have names as well as numbers: for example, group 17 elements are the halogens; and group 18, the noble gases. The periodic table can be used to derive relationships between the properties of the elements, and predict the properties of new elements yet to be discovered or synthesized. The periodic table provides a useful framework for analyzing chemical behavior, and is widely used in chemistry and other sciences.

Metal

A metal (from Greek μέταλλον métallon, "mine, quarry, metal") is a material (an element, compound, or alloy) that is typically hard, opaque, shiny, and has 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). About 91 of the 118 elements in the periodic table are metals, the others are nonmetals or metalloids. Some elements appear in both metallic and non-metallic forms.

Astrophysicists use the term "metal" to collectively describe all elements other than hydrogen and helium. Thus, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium.

Many elements and compounds that are not normally classified as metals become metallic under high pressures; these are formed as metallic allotropes of non-metals.

Structure and bonding