SME
Grade 10 Science · Problem type
Bond polarity from electronegativity
Use this to tell whether a bond is nonpolar, polar covalent or ionic from the electronegativity difference.
Diagram
Electronegativity of Hydrogen: 2.2.
Chlorine: 3.16, so Cl has the higher value.
Electronegativity increases across a period and decreases down a group; the stronger the shade, the larger the value.
Dashed cells have no value: helium, neon and argon form no compounds.
Difference in electronegativity: 0.96
This is an example. Type your own values to start a new problem.
ΔEN
=
|
EN₁
−
EN₂
|
Z₁
Atomic number of the first element
example
Z₂
Atomic number of the second element
example
Formulas
EN₁
=
electronegativity
of
element
Z₁
2.2 = electronegativity of element 1
EN₂
=
electronegativity
of
element
Z₂
3.16 = electronegativity of element 17
ΔEN = |EN₁ − EN₂|
0.96 = |2.2 − 3.16|
Assumptions
•
Under about 0.4 the bond is nonpolar, up to about 1.7 polar covalent, above that mostly ionic; books draw the lines a little differently.
•
The more electronegative atom takes the partial negative charge, δ−.
Step-by-step
WE KNOW
Z₁ = 1, Z₂ = 17
FIND
electronegativity of the first element (EN₁), electronegativity of the second element (EN₂), difference in electronegativity (ΔEN)
Step 1 · Find electronegativity of the first element (EN₁)
Use EN₁ = electronegativity of element Z₁
Read the element’s electronegativity from the table.
EN₁ = electronegativity of element 1
Z = 1 (hydrogen): period 1, group 1
EN₁ = 2.2
Step 2 · Find electronegativity of the second element (EN₂)
Use EN₂ = electronegativity of element Z₂
Read the element’s electronegativity from the table.
EN₂ = electronegativity of element 17
Z = 17 (chlorine): period 3, group 17
EN₂ = 3.16
Step 3 · Find difference in electronegativity (ΔEN)
Use ΔEN = |EN₁ − EN₂|
The size of the difference says how unevenly the shared pair is held.
ΔEN = |2.2 − 3.16|
0.4 ≤ 0.96 ≤ 1.7, so the bond is polar covalent; Z = 17 (chlorine), the more electronegative, takes δ−
ΔEN = 0.96
Check
Put the numbers back in. Both sides should match.
2.2 = electronegativity of element 1 ✓
3.16 = electronegativity of element 17 ✓
0.96 = |2.2 − 3.16| ✓
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Properties of ionic, molecular and metallic substances
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