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Polarity

Polarity. Chapter 6.1. Review. A covalent bond is formed between two non-metals. Electrons are shared. Orbitals are overlapping. A compound by definition has a neutral charge. However, sometimes atoms don’t share equally.

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Polarity

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  1. Polarity Chapter 6.1

  2. Review • A covalent bond is formed between two non-metals. • Electrons are shared. • Orbitals are overlapping

  3. A compound by definition has a neutral charge. However, sometimes atoms don’t share equally. A polar covalent bond is one in which a shared pair of electrons is held more closely to one atom. A non-polar covalent bond is one in which the electrons are shared equally. Polar and Non-polar

  4. Determining Bond Polarity • To determine the polarity in a bond between two atoms, you must use the value for electronegativity. • If the difference in () Electronegativity is >2.1, the bond is ionic. • If the  Electronegativity is <, the bond is covalent. •  Electroneg. is 2.1 – 0.5 the bond is polar •  Electroneg. Is < 0.5 the bond is non-polar

  5. Indicating Polarity • A dipole is a molecule or part of a molecule that contains both positively and negatively charged regions. • + is a positive dipole, the tendency of the least electronegative atom. • - is a negative dipole, the tendency of the most electronegative atom.

  6. Try Some • What is the polarity of the bond between: • C and O • C and H • C and C • Na and Cl • S and H • O and H • N and O • N and H Electronegativity Values C = 2.6 Cl = 3.2 H = 2.2 N = 3.0 O = 3.4 S = 2.6

  7. How strong are they? • The greater the difference in electronegativity, the stronger the bond is. • C and O • C and C • C and H • C and Se Electronegativity Values C = 2.6 Cl = 3.2 H = 2.2 N = 3.0 O = 3.4 Se = 2.5

  8. Molecular Polarity • The polarity of a molecule (compound) depends on two things. • The polarity of the bonds. • The shape of the molecule.

  9. Polarity based on bond types • If the compound has only non-polar covalent bonds or is a diatomic molecule, it is non-polar. • If the compound has polar covalent bonds, and the charges are symmetrical, the compound is non-polar. • If the compound has polar covalent bonds and asymmetrical charges (has dipoles), the compound is polar.

  10. Polarity based on shape • After determining the bond type, it is necessary to draw the Lewis Structure to determine the shape of the molecule. • If there is symmetry with the charge, then the compound is non-polar. • If there the charges are asymmetrical and there are dipoles, the compound is polar.

  11. VSEPR • Valence Shell Electron Pair Repulsion Theory • Shared and unshared pairs repel. • Lone pairs repel stronger than shared pairs. • Double and triple bonds are viewed as single; for structure only. • The resultant shape of the molecule is a result of shared and lone pairs being as far apart as possible.

  12. Table of Shapes

  13. Reactivities • The reactivity of a molecule is dependent on its shape. • The shape of a molecule is determined by its electron configuration.

  14. Polar Compounds Stronger intramolecular forces. Form ions when dissolved in water. Higher melting and boiling points. Conduct electricity in water. Non-polar Compounds Weak intramolecular forces. Do not form ions. Lower melting and boiling points. Do not conduct electricity. The properties of a substance depend in part on it’s polarity

  15. “Like dissolves like” • Polar compounds will dissolved other polar compounds, but not non-polar compounds. • Can you think of any examples?

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