Electronegativity: Pauling Scale
Electronegativity (ฯ) measures an atom's ability to attract electrons. Pauling scale: 0.7 (Cs) to 4.0 (F). ฮฯ predicts bond polarity: <0.4 nonpolar, 0.4โ1.7 polar covalent, โฅ1.7 ionic.
Why This Chemistry Calculation Matters
Why: Electronegativity predicts bond type, dipole direction, and reactivity. Essential for understanding molecular structure and chemical behavior.
How: Select two elements. Pauling scale from periodic table. ฮฯ = |ฯโ โ ฯโ|. Bond type: <0.4 nonpolar, 0.4โ1.7 polar, โฅ1.7 ionic.
- โF = 4.0 (highest); Cs = 0.7 (lowest).
- โฮฯ predicts bond polarity.
- โPauling, Mulliken, Allen scales.
Sample Bond Comparisons
๐ง NaCl (Sodium Chloride)
Ionic bond - large EN difference
โ๏ธ HCl (Hydrogen Chloride)
Polar covalent bond
๐ง H-O (Water bond)
Polar covalent, bent molecule
๐ก๏ธ C-O (Carbon Dioxide)
Polar covalent bonds
๐ข Cl-Cl (Chlorine gas)
Pure covalent - no EN difference
๐ Ca-F (Calcium Fluoride)
Highly ionic bond
๐ฅ C-H (Methane bond)
Slightly polar covalent
๐จ N-H (Ammonia bond)
Polar covalent
โซ C-O (Carbon Monoxide)
Triple bond, polar
๐ถ LiCl (Lithium Chloride)
Ionic/polar boundary
Quick Select Elements
Click to set Element 1, then Element 2
Compare Elements
โ ๏ธFor educational and informational purposes only. Verify with a qualified professional.
๐ฌ Chemistry Facts
Pauling scale: F=4.0, O=3.5, N=3.0, C=2.5, H=2.1.
โ Pauling
ฮฯ < 0.4: nonpolar; 0.4โ1.7: polar covalent; โฅ1.7: ionic.
โ Bonding
Mulliken: ฯ = (IE + EA)/2. Allen: configurational energy.
โ Scales
Electronegativity increases up and right on periodic table.
โ Trends
What is Electronegativity?
Electronegativity is a measure of an atom's ability to attract shared electrons in a chemical bond. Developed by Linus Pauling in 1932, it's one of the most important concepts for understanding chemical bonding and molecular properties.
Pauling Scale
The original and most widely used scale. Based on bond energies. Ranges from 0.7 (Cs) to 4.0 (F).
Mulliken Scale
Based on ionization energy and electron affinity. EN = (IE + EA)/2. More theoretical foundation.
Allen Scale
Based on average valence electron energy. Includes noble gases. Most recent scale (1989).
Periodic Trends in Electronegativity
Across a Period (โ)
Electronegativity increases left to right
- More protons โ stronger nuclear attraction
- Same shell โ effective nuclear charge increases
- Smaller atomic radius โ electrons held tighter
Down a Group (โ)
Electronegativity decreases top to bottom
- More shells โ greater atomic radius
- Increased shielding from inner electrons
- Valence electrons further from nucleus
Most electronegative: F (3.98) | Least electronegative: Cs (0.79)
Bond Types Based on Electronegativity Difference
Pure Covalent
ฮEN < 0.4
Equal sharing of electrons. Examples: Hโ, Oโ, Nโ, Clโ
Polar Covalent
0.4 โค ฮEN < 1.7
Unequal sharing, partial charges. Examples: HโO, HCl, NHโ
Ionic
ฮEN โฅ 1.7
Complete electron transfer. Examples: NaCl, CaFโ, MgO
Key Formulas
Mulliken Electronegativity
ฯPauling โ 0.359 ร ฯM0.5 + 0.744
Percent Ionic Character
(Hannay-Smyth equation)
Pauling's Original
where D = bond dissociation energy
Common Element Electronegativities
| Element | Symbol | Pauling EN | Category |
|---|---|---|---|
| Hydrogen | H | 2.20 | Nonmetal |
| Lithium | Li | 0.98 | Alkali Metal |
| Beryllium | Be | 1.57 | Alkaline Earth |
| Boron | B | 2.04 | Metalloid |
| Carbon | C | 2.55 | Nonmetal |
| Nitrogen | N | 3.04 | Nonmetal |
| Oxygen | O | 3.44 | Nonmetal |
| Fluorine | F | 3.98 | Halogen |
| Sodium | Na | 0.93 | Alkali Metal |
| Magnesium | Mg | 1.31 | Alkaline Earth |
| Aluminum | Al | 1.61 | Post-transition Metal |
| Silicon | Si | 1.90 | Metalloid |
| Phosphorus | P | 2.19 | Nonmetal |
| Sulfur | S | 2.58 | Nonmetal |
| Chlorine | Cl | 3.16 | Halogen |
Applications of Electronegativity
Predicting Reactivity
Highly electronegative atoms like F, O, N are strong oxidizers. Low EN elements like alkali metals are strong reducers.
Drug Design
Electronegativity affects drug solubility, membrane permeability, and receptor binding affinity in pharmaceutical design.
Material Science
EN differences determine semiconductor properties, catalyst activity, and corrosion resistance in materials.
Important Considerations
โ Key Points to Remember
- โข Fluorine has the highest electronegativity (3.98)
- โข Noble gases typically don't form bonds
- โข EN increases across a period, decreases down a group
- โข The 1.7 threshold for ionic bonds is approximate
- โข Multiple scales exist with different reference points
โ Common Misconceptions
- โข EN โ Electron affinity (related but different)
- โข Bond polarity doesn't always mean polar molecule
- โข Ionic/covalent is a spectrum, not binary
- โข EN values can vary slightly between sources
- โข Oxidation state can affect an atom's EN