Chemistry · Periodic Classification Of Properties · NEET
The correct increasing order is Si < C < N < O < F. Here is the simple logic. Si is in period 3, so it is a big atom and pulls electrons weakly, making it the least electronegative. C, N, O and F are all in period 2. Moving left to right across period 2, the nuclear pull (Z_eff) rises and the size shrinks, so electronegativity rises: C < N < O < F. Fluorine sits at the top. This exact order was asked in NEET 2024.
It DECREASES down a group. As you go down, a new shell is added each time, so the atom gets bigger. The bonding electrons are farther from the nucleus and are shielded by inner shells, so the nucleus cannot pull them strongly. Bigger atom = weaker pull = lower electronegativity. That is why F (top of group 17) is far more electronegative than I (bottom).
Across a period from left to right, protons are added to the nucleus but electrons go into the SAME shell. So the effective nuclear charge (Z_eff) rises and the atomic radius shrinks. A smaller atom with a stronger nuclear pull grabs shared electrons more tightly. So electronegativity rises from Li to F in period 2. Short rule: smaller radius and higher Z_eff mean higher electronegativity.
Electron gain enthalpy is the energy released when a FREE, isolated gaseous atom gains an electron - it is a measurable energy value for a lone atom. Electronegativity is the tendency of an atom to attract SHARED electrons when it is already inside a chemical bond - it is not measurable and has no units, only scale numbers (like the Pauling scale). Both increase across a period and decrease down a group, but electron gain enthalpy is for a lone atom while electronegativity is only meaningful inside a compound.
No. NCERT is clear that electronegativity is NOT a measurable quantity and it is not constant. Its value depends on the element an atom is bonded to and even on the hybridisation of the atom. So the statement 'the electronegativity of N is 3.0 in ALL nitrogen compounds' is wrong. We only use approximate scale values (Pauling scale, where F = 4.0) to compare elements.
Fluorine is a very small period-2 atom with a high effective nuclear charge and only one shell shielding its bonding electrons. Its outer electrons sit very close to the nucleus, so it pulls shared electrons extremely strongly. Pauling gave it the highest scale value, 4.0. Because of this, fluorine also never shows a positive oxidation state.
Arrange the following elements in increasing order of electronegativity: N, O, F, C, Si.
The correct order of increasing metallic character of Na, Be, P, Mg and Si is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Fluorine has the highest electronegativity of all elements, with a Pauling scale value of 4.0. It is a small period-2 atom with a high nuclear pull, so it attracts shared electrons more strongly than any other element.
No. Electronegativity is not a measurable physical quantity, so it has no units. We only use relative scale numbers, most commonly the Pauling scale, to compare elements against each other.
They are inversely related. A smaller atomic radius means the bonding electrons are closer to the nucleus and are pulled harder, so electronegativity is high. As the radius grows (down a group), electronegativity falls.
High electronegativity means strong tendency to gain electrons, so it goes with non-metallic character. Low electronegativity goes with metallic character. So across a period non-metallic character rises, and down a group metallic character rises.
No. Electronegativity is not constant - it changes with the atom nitrogen is bonded to and with hybridisation. The value 3.0 is only an average approximate scale value, not a fixed number for every nitrogen compound.
