On heating an alkali metal or its salt (especially chlorides due to its more volatile nature in a flame), the electrons are excited easily to higher energy levels because of absorption of energy. The alkali metals and their salts impart a characteristic colour to flame Li does not emit photoelectrons due to high value of ionization energy. The ability to exhibit photoelectric effect is due to low value of ionization energy of alkali metals.
Reactivity trend of alkali earth metals free#
This is due to the presence of loosely held valence electrons which are free to move throughout the metal structure.Īlkali metals (except Li) exhibit photoelectric effect (A phenomenon of emission of electrons from the surface of metal when light falls on them). The alkali metals are good conductors of heat and electricity. The ionization energy of alkali metals decreases down the group. The first ionization energy of the alkali metals are the lowest as compared to the elements in the other group. The charge density on Li+ is higher in comparison to other alkali metals due to which it is extensively hydrated. Thus, the ionic radii in aqueous solution follow the order
Smaller the ion more is the extent or degree of hydration. The alkali metal ions get extensively hydrated in aqueous solutions. However, within the group the ionic radii increase with increases in atomic number. The size of cation is smaller than parent atom of alkali metals. Hence the atomic size increases in a group.Īlkali metals change into positively charged ions by losing their valence electron. Although, the nuclear charge also increases down the group but the effect of addition of new shells is more predominant due to increasing screening effect of inner filled shell on the valence s-electrons. On moving down the group a new shell is progressively added. The general electronic configuration of alkali metals may be represented by where n = 2 to 7 Beryllium is sufficiently hard to scratch glass, but barium is only slightly harder than lead. They have a gray-white lustre when freshly cut but tarnish readily in air, particularly the heavier members of the group. For example NaOH and KOH Francium is radioactive and has a very short life (half life of 21 minutes), therefore very little is known about it. The alkaline-earth elements are highly metallic and are good conductors of electricity. These are called alkali metals because hydroxides of these metals are strong alkali.
The group I comprising Li, Na, K, Rb, Cs & Fr are commonly called alkali metals.
Concepts of Physics by HC Verma for JEE.IIT JEE Coaching For Foundation Classes.
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