9701 · 3.1
Electronegativity and bonding flashcards
Revision flashcards for Cambridge 9701 Electronegativity and bonding (syllabus 3.1). Flip, recall, then mark a real past-paper question.
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What is electronegativity?
The ability of a bonded atom to attract the pair of electrons in a covalent bond.
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What is the trend in electronegativity across a period?
It increases. The nuclear charge increases while the shielding effect remains relatively constant, pulling the bonding electrons more strongly.
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What is the trend in electronegativity down a group?
It decreases. The atomic radius and shielding both increase, so the nucleus has a weaker attraction for the bonding electrons.
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What is a non-polar covalent bond?
A bond where the electrons are shared equally between two atoms. This occurs when the electronegativity difference (ΔEN) is zero or very small (e.g., in diatomic elements like O₂ or Cl₂).
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What is a polar covalent bond?
A bond where electrons are shared unequally. The more electronegative atom gains a partial negative charge (δ⁻), and the less electronegative atom gains a partial positive charge (δ⁺).
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What is a dipole moment?
A measure of the separation of two opposite electrical charges. In chemistry, it refers to the partial charges on atoms in a polar bond or molecule, creating a positive and a negative pole.
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What symbol is used to represent a partial charge?
The lowercase Greek letter delta: δ⁺ for a partial positive charge and δ⁻ for a partial negative charge.
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Can a molecule with polar bonds be non-polar overall?
Yes. If the polar bonds are arranged symmetrically in space, their individual dipoles cancel each other out. A key example is carbon tetrachloride, CCl₄.
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Which is the most electronegative element?
Fluorine (F). It is at the top right of the periodic table (excluding noble gases).
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What approximate electronegativity difference (ΔEN) suggests an ionic bond?
A difference greater than approximately 1.7. However, this is a guideline, not a strict rule; bonding is a continuum.
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Why is CHCl₃ (trichloromethane) a polar molecule while CCl₄ (tetrachloromethane) is not?
In CCl₄, the four identical C-Cl bond dipoles are arranged symmetrically in a tetrahedron and cancel out. In CHCl₃, the C-H bond has a different polarity to the C-Cl bonds, creating an asymmetrical arrangement of dipoles that results in a net molecular dipole.