Chemistry · Chemical Bonding · NEET
The octet rule says an atom is most stable when its outermost shell holds 8 electrons. This is the same number that noble gases (like Neon and Argon) already have. So other atoms try to copy noble gases by losing, gaining, or sharing electrons until they reach 8. This 8-electron arrangement has low energy, which means it is stable. For NEET, remember: bonding happens BECAUSE atoms are trying to complete their octet.
The number of dots equals the number of valence electrons (the electrons in the outermost shell). For example, oxygen is in group 16, so it has 6 valence electrons and 6 dots. Sodium is in group 1, so it has 1 dot. Quick trick: for main-group elements, the group number tells you the dots (group 1 = 1 dot, group 17 = 7 dots). NEET often tests whether you can write the correct dot symbol for an atom or ion.
Noble gases have 8 electrons in their outer shell (except helium, which has 2) and they almost never react. This tells us that 8 outer electrons is a very stable, low-energy setup. Other atoms are not this stable, so they combine with each other to reach that same 8-electron count. The number 8 is special only because it matches the stable noble-gas configuration, not for any magic reason.
A Lewis symbol is a drawing: the element symbol with dots for its valence electrons (for example, N with 5 dots). The octet rule is the idea that atoms combine to get 8 electrons around them. So the Lewis symbol shows you WHAT electrons an atom starts with, and the octet rule tells you WHY it bonds. You use the Lewis symbols to build molecules that follow the octet rule.
No. Hydrogen follows the duplet rule. It only needs 2 electrons in its outer shell to become stable, because it copies helium, the nearest noble gas, which has just 2 electrons. So in molecules like H2 or CH4, each hydrogen atom is happy with a share of 2 electrons, not 8. This is a common NEET trap, so always treat H as duplet, not octet.
Valence electrons are only the outer-shell electrons; inner-shell electrons are not counted because they are well protected and do not take part in bonding. Write the electron configuration and look at the highest shell. For example, chlorine is [Ne]3s2 3p5, so the outer shell (n=3) has 2+5 = 7 electrons, giving 7 dots. NCERT states clearly that only outer-shell electrons take part in chemical combination.
For the ozone (O3) Lewis structure — a central O atom (1) doubly bonded to one terminal O atom (2) and singly bonded to the other terminal O atom (3) — the correct formal charges on the oxygen atoms numbered 2, 1 and 3 respectively are:
Consider the molecules CH4, NH3 and H2O. Which of the given statements is FALSE?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Kössel and Lewis developed the electronic theory of chemical bonding in 1916. According to it, atoms combine by transferring or sharing valence electrons so that each atom gets 8 electrons in its outer shell, which is the octet rule.
Group valence is the combining power of an element. From a Lewis symbol, it is usually equal to the number of dots (valence electrons) or to 8 minus the number of dots, whichever is smaller. For example, oxygen has 6 dots, so its valence is 8 - 6 = 2.
No. It works best for second-period elements (like C, N, O, F) and most organic compounds. It fails for hydrogen (duplet), for incomplete octets (BeH2, BCl3), for odd-electron molecules (NO, NO2), and for expanded octets (PCl5, SF6).
A Lewis symbol shows one atom with its valence electrons as dots (like O with 6 dots). A Lewis structure (or Lewis dot structure) shows a whole molecule, with shared electron pairs as bonds and the leftover electrons as lone pairs.
An outer shell with 8 electrons is the same configuration noble gases have, and it corresponds to a low energy state. Nature prefers low energy, so atoms bond to reach this stable octet, which lowers the energy of the system.
