Electronegativity Calculator

Pauling (1932) defined electronegativity from bond energy differences: chi_A - chi_B = sqrt(D(A-B) - [D(A-A)+D(B-B)]/2) / 96.48 (kJ/mol)^0.5, where D is bond dissociation energy. He set fluorine's electronegativity to 4.0 (later revised to 3.98). The scale ranges from Cs (0.79) to F (3.98). It is semi-empirical and based on experimental bond energies.

By convention, delta_chi > 1.7 is considered ionic, delta_chi 0.4-1.7 is polar covalent, and delta_chi < 0.4 is nonpolar covalent. However, these are guidelines, not sharp boundaries. The transition from covalent to ionic is gradual. Even NaF (delta_chi = 3.05) retains some covalent character, and even H2 (delta_chi = 0) has very slight charge fluctuations (instantaneous dipoles).

The dipole moment mu = q * d, where q is the charge magnitude and d is the bond length. For a purely ionic bond, q = e (elementary charge) and mu would be maximum. The actual dipole moment divided by the maximum ionic value gives the percent ionic character by another measure. This method gives somewhat different values than Pauling's formula.

Allen's (1989) spectroscopic scale uses orbital energies: chi = (n_s * e_s + n_p * e_p) / (n_s + n_p). Allred-Rochow (1958) uses effective nuclear charge: chi = (0.744 + 0.359*Z_eff) / r^2. Sanderson uses atomic radius and electron density. All scales correlate reasonably well with each other and with Pauling's for main group elements.

Fluorine has 9 protons and 7 valence electrons (F: [He] 2s^2 2p^5). Oxygen has 8 protons and 6 valence electrons. Fluorine's higher nuclear charge in the same period means stronger attraction of the 2p electrons toward the nucleus, and attraction for bonding electrons is stronger. The trend of increasing electronegativity across a period reflects increasing nuclear charge with similar atomic size.

When atoms form a bond, electrons redistribute until all atoms reach the same electronegativity (chemical potential equalization principle). The final electronegativity of the bonded atoms is the geometric mean of the original electronegativities (Sanderson's principle). This principle is used in molecular mechanics and QSAR (quantitative structure-activity relationships).

Molecular polarity depends on both bond polarity (from electronegativity differences) and molecular geometry. CO2 has two polar C=O bonds (delta_chi = 0.89) but is nonpolar because the linear geometry cancels the bond dipoles. H2O has two polar O-H bonds and a bent geometry, so the dipoles add — giving water its large dipole moment (1.85 Debye).

Yes. Electronegativity is not a fixed atomic property but depends on hybridization, oxidation state, and the chemical environment. An sp3 carbon has lower electronegativity than an sp carbon. Oxygen in an alcohol is less electronegative than in a carbonyl. These variations are captured by orbital electronegativities in computational chemistry but are approximated as fixed values in Pauling's scale.

The inductive effect is the transmission of electronegativity differences through a chain of bonds. A highly electronegative substituent (like F or Cl) withdraws electron density not just from its directly bonded neighbor but from atoms further along the chain, with decreasing effect. This is important in organic chemistry for predicting acidity, basicity, and reaction rates.