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Alkali Metals and Halogens

Alkalimetals and halogens are the chemical elements which are members of the group 1 and group 17 in the periodic table. They are called as s-block elements and p-block elements respectively.

Alkalimetals have the differentiating electron which enters the s-orbital of the valence shell. The general outermost electronic configuration of s-block elements is ns1-2 .

Halogensare in p-block, in this block the differentiating electron which entersthe p-orbital of the valence shell. The general outermost electronic configuration of p-block elements is ns2 np1-6.

Examples of alkali metals: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), ceasium (Cs), and francium (Fr). 

Although Hydrogen, is a member of group sometimes exhibit the properties of alkali metals. Examples of halogens are Fluorine (F), Chlorine (Cl), Bromine (Br) and Iodine (I).

Reactivity of alkali metals and halogens

Inthe outermost (s) shell of the alkali metals, they have 1 electron, by loosing that electron, the alkali metals get the stable electronic configuration. In case of halogens, they are electron short in the outermost (p) shell, adding an electron it creates a stable electronic configuration. As we move from lithium to francium, the electrons are further more away from the nucleus, hence it is easy to remove an electron from the outermost shell.

Incase of halogens, when we go up in the series, the electrons are much closer to the nucleus hence more will be the electro negativity of the element.

Hence in the alkali metals and halogens, the most reactivity combination would be ceasium – fluoride.

Thecommon thing in both alkali metals and halogens is the chemistry of loosing and gaining the electrons. Since the alkali metals and halogens comes under 1st group and 17th group, they have one electron and seven electrons in the outermost shell. Alkali metals lose an electron to gain valency +1 and halogens gain an electron to attain -1 valence. In this way, both posses same valence number but one looses and one gains. Hence this is also the major reason for the attraction of these elements.

Examples for the reaction of Alkali metals with Halogens:

  • Lithium + fluorine → lithium fluoride.
  2Li(s)  +    F2(g)              2LiF(s)
  • Lithium + chlorine → lithium chloride.
  2Li(s)  +    Cl2(g)              2LiCl(s)
  • Lithium + bromine → lithium bromide.
  2Li(s)  +    Br2(l)              2LiBr(s)
  • Lithium + iodine  →  lithium iodide.
  2Li(s)  +    I2(s)              2LiI(s)

Properties of alkali metals and halogens

Alkali metals:

  • Alkali metals have less density compared to other metals.

  • They have loosely bound valence electron.

  • They contain large radii in the periods

  • They have low ionization energy and electronegativity.

  • They are highly reactive in nature.


  • These are high reactive elements in the group and have high electron affinity.

  • They have low dissociation energy  which means they can dissociate very easily to combine with other substances.

  • They are highly volatile and are readily reacted with alkali metals and alkaline earth metals.

  • Halogens readily react with hydrogen to form hydrogen halides as binary compounds.