Question

Discuss the general characteristics and gradation in properties of alkaline earth metals.

Answer 1

In the s-block elements of periodic table, the last electron enters in the outermost s-orbital. As s- orbital can accommodate only two electrons, only 2 groups belong to s- block of the periodic table. The group 1 elements are known as alkali earth metals, and group 2 elements are called as alkaline earth metals.

Complete answer:
In the periodic table, s-block has 2 groups. One is alkali metals because the elements of this group form hydroxide on reaction with water which is strongly alkaline. The second group is known as alkaline earth metals as their oxides and hydroxides are alkaline in nature and these metal oxides are found in the earth’ crust. In the above question we are talking about group 2 elements
The group 2 elements comprise beryllium, magnesium, calcium, strontium, barium and radium. The first element beryllium differs from the rest elements and shows diagonal relationship with aluminium.
Electronic configuration: Since they have two electrons in the outermost s- orbital, their general electronic configuration may be represented as [noble gas] $n{s^2}$.
Atomic and ionic radii: Size are smaller than those of alkali metals in the same period due to decrease in the nuclear charge. Atomic size increases down the group as a new orbital shell has increased and effective nuclear charge hence decreased.
Oxidation state These metal lose 2 electrons to get noble gas configuration, hence their general oxidation state is +2
Ionization enthalpies have low ionization enthalpies due to fairly large size of atoms. Ionization enthalpy increases down the group
Hydration enthalpies: Hydration enthalpy of these metals ions decrease with increase in ionic size, which increases down the group.
Physical properties: They are generally silvery white, lustrous and relatively soft but harder than alkali metals.
Melting and boiling point- melting and boiling points are higher than corresponding alkali metals, since these metals are smaller than alkali metals and they have two valence electrons for the formation of metallic bonds.
Electropositive character: The electropositive character increases down the group due to low ionization enthalpies.
Flame colors: Calcium, strontium and barium impart brick red, crimson and apple green colors to the flame respectively. While the beryllium and magnesium do not impart any color.
Reactivity: These metals are less reactive than alkali metal. Their reactivity increases down the group.

Note:
Beryllium is used in the manufacture of alloys. Copper-beryllium alloys are used in the preparation of high strength springs. Magnesium- aluminium alloys being light are used in aircraft construction. Magnesium hydroxide acts as antacid. Calcium is used in extraction of metals from oxides which are difficult to reduce with carbon. Calcium and barium used to remove air from vacuum. Radium salts are used in radiotherapy.