Question

Why‌ ‌are‌ ‌they‌ ‌called‌ ‌Alkaline‌ ‌Earth‌ ‌metals?‌ ‌

Answer 1

The alkaline earth metals are six chemical elements in group $2$ of the periodic table. They are beryllium $(Be)$, magnesium $(Mg)$, calcium $(Ca)$, strontium $(Sr)$, barium $(Ba)$ and radium $(Ra)$. The elements have very similar properties.

Complete answer:
The alkaline earth metals are named after their oxides, these oxides are basic (alkaline) when combined with water. “Earth” was a term applied by early chemists to nonmetallic substances that are insoluble in water and resistant to heat. Antoine Lavoisier called them salt-forming earth elements.
Alkali metal structurally, have in common an outer s-orbital which is full, that is, this orbital contain its full complement of two electrons, which the alkaline earth metal readily lose to form cations with charge $+ 2$, and an oxidation state of $+ 2$. All the discovered alkaline earth metals occur in nature, although radium occurs only through the decay chain of uranium and thorium and not as a primordial element.
Some characteristics of alkaline earth metals are:
$1.$ Chemical- the alkaline earth metal show patterns in their electronic configuration, especially the outermost shells, resulting in trends in chemical behavior.

Atomic Number $(Z)$	Elements	Number of electrons/shell	Electronic configuration
$4$	Beryllium	$2,2$	$[He]2{s^2}$
$12$	Magnesium	$2,8,2$	$[Ne]3{s^2}$
$20$	Calcium	$2,8,8,2$	$[Ar]4{s^2}$
$38$	Strontium	$2,8,18,8,2$	$[Kr]5{s^2}$
$56$	Barium	$2,8,18,18,8,2$	$[Xe]6{s^2}$
$88$	Radium	$2,8,18,32,18,8,2$	$[Rn]7{s^2}$

The alkaline earth metals are all silver colored and soft, and have relatively low densities, melting point and boiling point. In chemical terms, all of the alkaline earth metals react with the halogens to form the alkaline earth metals halides such as calcium chloride $(CaC{l_2})$, as well as reacting with oxygen to form oxide such as strontium oxide $(SrO)$, all of which are ionic crystalline compounds (except for beryllium chloride, which is covalent).
All alkaline earth metals except beryllium also react with water to form strongly alkaline hydroxides and thus, should be handled with great care. The heavier alkaline earth metals react more vigorously than the lighter ones. The alkaline earth metals have the second-lowest first ionization energies in their respective periods of the periodic table because of their somewhat low effective nuclear charges and the ability to attain a full outer shell configuration by losing just two electrons.
$(2)$ Physical and atomic- The lowest atomic weight in alkaline earth metal is of beryllium $(9.01u)$ and highest of Radium $(226u)$.
Melting point- Lowest melting point is of Magnesium i.e $(923K)$ and highest melting point is Beryllium $(1560K)$.
Boiling point- Lowest boiling point is of Magnesium i.e $(1363K)$ and highest boiling point is Beryllium $(2742K)$.
Density- Lowest density is of Calcium $(1.54g/c{m^3})$ and highest density is of Radium $(5.5g/c{m^3})$.
$(3)$ Representative reactions of alkaline earth metals-
Reaction with halogens:
$Ca + C{l_2} \to CaC{l_2}$ (calcium chloride)
Reaction with Oxygen:
$Ca + \dfrac{1}{2}{O_2} \to CaO$ (Calcium oxide)
$Mg + \dfrac{1}{2}{O_2} \to MgO$ (Magnesium oxide)
Reaction with Sulphur:
$Ca + \dfrac{1}{8}{S_8} \to CaS$ (Calcium Sulphide)
Reaction with Carbon:
$2Be + C \to B{e_2}C$
Reaction with Nitrogen:
$3Be + {N_2} \to B{e_3}{N_2}$
$3Mg + {N_2} \to M{g_3}{N_2}$

Note:
Out of six alkaline earth metals, beryllium, calcium, barium and radium have at least one naturally occurring radioisotope; magnesium and strontium do not. Beryllium $- 7$, Beryllium $3Mg + {N_2} \to M{g_3}{N_2}$ and calcium $- 41$ are trace radioisotopes; calcium $- 48$ and barium $- 130$.
Magnesium and calcium are essential to all living organisms, Magnesium functions as the active center in some enzymes, and Calcium salts take a structural role, most notably in bones.
Strontium plays an important role in marine aquatic life, especially hard corals, which use strontium to build their exoskeletons. Barium has some use in medicine.