IB Chemistry Topic S2.2.5 Bond Polarity Revision Notes (SL/HL)

IB Chemistry Topic S2.2.5 Bond Polarity Revision Notes (SL/HL) | RevisionDojo

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Electronegativity Differences and Dipole Moments in Covalent Bonds

Definition

Electronegativity

Electronegativity is the ability of an atom to attract shared electrons in a covalent bond.

Analogy

Think of it as a "tug-of-war" for electrons: the stronger the atom's pull, the higher its electronegativity.

Example

Fluorine (F), the most electronegative element, has a value of 4.0.
Hydrogen (H), with a lower electronegativity of 2.2, exerts a weaker pull.

Electronegativity Differences and Bond Types

The difference in electronegativity ($\Delta \chi$) between two bonded atoms determines the type of bond they form:

Nonpolar Covalent Bond ($\Delta \chi = 0$): Electrons are shared equally (e...g., $H_2$).
Polar Covalent Bond ($0 < \Delta \chi < 1.8$): Electrons are shared unequally, creating partial charges (e...g., $HCl$).
Ionic Bond ($\Delta \chi > 1.8$): Electrons are transferred completely, forming ions (e...g., $NaCl$).

Example

Classifying Bond Types

Carbon–Hydrogen (C–H):
- Electronegativity of C = 2.6, H = 2.2.
- $\Delta \chi = |2.6 - 2.2| = 0.4$, so the bond is slightly polar covalent.
Hydrogen–Fluorine (H–F):
- Electronegativity of H = 2.2, F = 4.0.
- $\Delta \chi = |4.0 - 2.2| = 1.8$, so the bond is highly polar covalent.

Note

Electronegativity differences provide a guideline, but remember that bonding exists on a continuum rather than in strict categories.

Hint

Electronegativity values can be found in Section 9 of the Data Booklet.

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Electronegativity Differences and Dipole Moments in Covalent Bonds

Definition

Electronegativity

Electronegativity is the ability of an atom to attract shared electrons in a covalent bond.

Analogy

Think of it as a "tug-of-war" for electrons: the stronger the atom's pull, the higher its electronegativity.

Example

Fluorine (F), the most electronegative element, has a value of 4.0.
Hydrogen (H), with a lower electronegativity of 2.2, exerts a weaker pull.

Electronegativity Differences and Bond Types

The difference in electronegativity ($\Delta \chi$) between two bonded atoms determines the type of bond they form:

Nonpolar Covalent Bond ($\Delta \chi = 0$): Electrons are shared equally (e...g., $H_2$).
Polar Covalent Bond ($0 < \Delta \chi < 1.8$): Electrons are shared unequally, creating partial charges (e...g., $HCl$).
Ionic Bond ($\Delta \chi > 1.8$): Electrons are transferred completely, forming ions (e...g., $NaCl$).

Example

Classifying Bond Types

Carbon–Hydrogen (C–H):
- Electronegativity of C = 2.6, H = 2.2.
- $\Delta \chi = |2.6 - 2.2| = 0.4$, so the bond is slightly polar covalent.
Hydrogen–Fluorine (H–F):
- Electronegativity of H = 2.2, F = 4.0.
- $\Delta \chi = |4.0 - 2.2| = 1.8$, so the bond is highly polar covalent.

Note

Electronegativity differences provide a guideline, but remember that bonding exists on a continuum rather than in strict categories.

Hint

Electronegativity values can be found in Section 9 of the Data Booklet.

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Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

IB Chemistry S2.2.5 Bond Polarity Notes

Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

Electronegativity Differences and Dipole Moments in Covalent Bonds

Electronegativity Differences and Bond Types

Classifying Bond Types

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Electronegativity Differences and Dipole Moments in Covalent Bonds

Electronegativity Differences and Bond Types

Classifying Bond Types

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