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Alkali & Alkaline Earth Metals

 The third liquid element The third liquid element In periodic table, two elements mercury (Hg, Z=80) and bromine (Br, Z=35) exist as liquid state at room temperature (25°C). Francium (Fr, Z=87) belongs IA group (alkali metals) is the third liquid element in the periodic table with melting point 27°C. Francium is the only radioactive alkali metal producing heat that even few milligrams of it would end up in glowing fume immediately.

Learning Objectives

After completing the topic, the student will be able to:

  • List alkali metals and alkaline earth metals, write their electronic configurations.
  • Explain the physical and chemical properties of alkali and alkaline earth metals.
  • Discuss the exceptions in general periodic trends in s–block elements.
  • Describe the preparation methods, general characteristics of compounds of sodium, potassium, magnesium and calcium; and give their uses
  • Recognize the biological significance of sodium, potassium, magnesium and calcium.
s-Block elements s–block elements In the periodic table the s–block is the block in which the alkali and alkaline earth metals are present. The s–block elements have the differentiating or the outermost electron(s) in the ns–orbital.
s-block elements

Elements in which all inner electron shells are completely filled, and the last electron enters the s–orbital of the outermost shell, are called s–block elements. Thus, for s–block elements, the differentiating electron enters the ns–orbital. Therefore, the outermost electronic configuration of the s–block elements is ns1 or ns2, all inner orbitals being completely filled. In modern periodic table s–block elements are placed in first two groups &ndash Group 1 or IA Group and Group 2 or IIA Group.

Group 1 elements are called alkali metals. Alkali metals are named after the Arabic word ‘al–qis’, meaning plant ash because the ash of plants is rich in the carbonates of sodium and potassium.

Group 2 elements are called alkaline earth metals because of the alkaline (basic) nature of their oxides, for the basic solutions the elements form in water and as these elements are naturally found in the earth's crust.

Group 1 and 2 elements provide the best example of regular trends with no significant exceptions. All the elements in the group 1 – Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), radioactive Francium (Fr). Mnemonic: Lilly and Nasty Kids Rub the Cats Fu r

Group 2 – Beryllium(Be), Magnesium(Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), radioactive Radium (Ra) are very reactive metals. Mnemonic: Beer Mugs Can Serve Bar Rats

Electronic configurations of alkali metals

The configurations show that the ultimate shells of alkali metals have one s electrons (s1 electron) while the penultimate shell contains eight (s2p6) electrons (Li is exception). When this valence–shell electron is lost, the alkali metals are converted into M+ ions which have inert gas configuration. Since the additional electron enters ns–orbital, these are s–block elements.

Why hydrogen is not placed in IA group even though its electron enters in s orbital ?
Due to its unique properties, the place of hydrogen is not justified along with the alkali metals or with the halogens i.e., group 17 of the periodic table. As it loses one electron to form a unipositive ion, forms oxides, sulfides and halides. But due to high ionization enthalpy (metals will have low ionization enthalpy) it is not considered as a metal. Like halogens it forms a diatomic molecule, a hydride and covalent compounds. But it doesn't resemble the halogens in terms of reactivity as it is very less reactive comparatively. Thus hydrogen has similarities and differences with both alkali metals and halogens.

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