Chemistry · Chemical Bonding · NEET
Write the electronic configuration and count the electrons in the OUTERMOST shell (highest n number). Example: oxygen is 1s2 2s2 2p4. The outer shell is n=2, which has 2 + 4 = 6 electrons. So oxygen has 6 valence electrons. Inner shells (like 1s2) do NOT count. For main-group elements, the valence electrons also equal the group number (in the 1-18 system, subtract 10 for groups 13-18).
Valence electrons = how many electrons are in the outer shell (a count of electrons). Group valence = how many bonds the atom usually forms (its combining power). They are related by the NCERT rule: group valence is either equal to the number of valence electrons, OR equal to 8 minus the number of valence electrons. You take the smaller value. Oxygen has 6 valence electrons, but its group valence is 8 - 6 = 2, because forming 2 bonds is easier than forming 6.
Oxygen wants a full octet of 8 electrons. It has 6, so it only needs 2 more. Gaining or sharing 2 electrons is much easier than losing 6. So oxygen forms 2 bonds, and its group valence is 8 - 6 = 2. This is exactly the '8 minus valence electrons' part of the NCERT rule. It matters for NEET because you use it to predict formulas like H2O and CO2.
Use the number of dots (valence electrons) directly for elements with FEW outer electrons, because they lose or share those few. Example: sodium has 1 valence electron, so valence = 1; carbon has 4, so valence = 4. Use '8 minus dots' for elements with MANY outer electrons (5, 6, or 7), because they gain or share the few electrons needed to reach 8. Example: nitrogen (5) gives 8 - 5 = 3; chlorine (7) gives 8 - 7 = 1. Simple rule: always pick the smaller number.
A Lewis symbol (Lewis dot symbol), introduced by G.N. Lewis, is the element symbol with dots around it. Each dot is one valence electron. For example, nitrogen has 5 valence electrons, so its Lewis symbol shows N with 5 dots. NCERT says: the number of dots equals the number of valence electrons, and this number helps you calculate the group valence.
No. NCERT clearly states that only the outer-shell (valence) electrons take part in chemical combination. The inner-shell electrons are well protected by the nucleus and are generally not involved in bonding. So when counting valence electrons, ignore all fully-filled inner shells and count only the outermost shell.
The correct statement is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Group valence = number of valence electrons, OR = 8 - (number of valence electrons), whichever gives the smaller value. This is the exact NCERT rule from the chapter Chemical Bonding and Molecular Structure.
Carbon (1s2 2s2 2p2) has 4 valence electrons. Its group valence is 4, because 4 equals '8 minus 4' - both give 4. This is why carbon forms four bonds, as in CH4.
No. Valence electrons are the count of outer-shell electrons. Valency (group valence) is the combining power, found using the 'dots or 8-minus-dots' rule. They are equal only when the atom has 4 or fewer valence electrons; for 5, 6 or 7 outer electrons they differ.
For main-group atoms following the octet rule, the outer shell holds a maximum of 8 electrons (2 in s + 6 in p). Noble gases (except helium) have this full octet, which is why they are stable and unreactive.
It lets you quickly predict how many bonds an atom forms and therefore the correct molecular formula (H2O, NH3, CO2). NEET also tests the difference between valence electrons and valence orbitals, and maximum covalency, so knowing this rule prevents common trap answers.
