Chemistry · Periodic Classification Of Properties · NEET
ns¹ means the outermost shell has exactly one electron in the s-orbital. The 'n' is the period number (the row). So Li in period 2 is 2s¹, Na in period 3 is 3s¹, K in period 4 is 4s¹. Every Group 1 metal ends in this same ns¹ pattern. NEET often gives you a configuration like [Ne]3s¹ and asks the group — that ns¹ ending tells you it is Group 1, an alkali metal (this is sodium).
They have just one loosely held outer electron. Removing that one electron gives a stable noble-gas configuration (a full shell), so it comes off very easily — their first ionization enthalpy is low. But removing a second electron means breaking into the stable noble-gas core, which needs a huge amount of energy. So they stop at +1. That is why sodium is Na⁺, never Na²⁺.
They are s-block. NCERT groups elements by which sub-shell the last electron enters. Group 1 (ns¹) and Group 2 (ns²) fill the s-orbital, so both are s-block. Alkali metals = Group 1 s-block. Do not confuse them with halogens or noble gases, which are p-block.
As you go down, the atom gets bigger and the outer electron sits farther from the nucleus. It is held more weakly, so ionization enthalpy decreases down the group and the electron is lost more easily. Losing the electron is what makes them react, so caesium is far more reactive than lithium. NCERT says metallic character and reactivity increase down the group.
No. Hydrogen also has an ns¹-type configuration (1s¹) and is placed at the top of Group 1, but it is NOT a true alkali metal. Hydrogen is a non-metal gas, it can also gain an electron to form H⁻, and it does not behave like Na or K. This is called the anomalous position of hydrogen. Alkali metals are only Li, Na, K, Rb, Cs, Fr.
Because they are so reactive. Their low ionization enthalpy means they lose their electron very fast to air, water, and other elements, forming compounds instantly. So they always exist combined (like NaCl, common salt), never as free metal. That is why they are stored under kerosene oil.
Which among the following electronic configurations belong to main group elements? A. [Ne]3s¹ B. [Ar]3d³4s² C. [Kr]4d¹⁰5s²5p⁵ D. [Ar]3d¹⁰4s¹ E. [Rn]5f⁰6d²7s²
In which option does the order NOT agree with the property indicated? (checking metallic radius trend in Group 1)
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Six: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Francium is radioactive and very rare.
ns¹, where n is the period number. Li = 2s¹, Na = 3s¹, K = 4s¹, Rb = 5s¹, Cs = 6s¹, Fr = 7s¹.
They have a single outer electron far from the nucleus, shielded by inner shells. Very little energy is needed to remove it, and doing so gives a stable noble-gas configuration.
Caesium (Cs) is the most reactive of the common alkali metals, because its outer electron is farthest from the nucleus and easiest to lose. Reactivity increases down the group.
Lithium is a bit different. Because Li⁺ is very small with high polarising power, lithium compounds have more covalent character than the others. NCERT notes lithium as the exception among s-block compounds.
