Polarity Chapter 6.1. Review A covalent bond is formed between two non-metals. Electrons are shared. Orbitals are overlapping.

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Presentation transcript:

Polarity Chapter 6.1

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

Polar and Non-polar 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.

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

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.

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 = 2.6Cl = 3.2 H = 2.2N = 3.0 O = 3.4S = 2.6

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 = 2.6Cl = 3.2 H = 2.2N = 3.0 O = 3.4Se = 2.5

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

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.

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.

VSEPR Valence Shell Electron Pair Repulsion Theory 1. Shared and unshared pairs repel. 2. Lone pairs repel stronger than shared pairs. 3. Double and triple bonds are viewed as single; for structure only. 4. The resultant shape of the molecule is a result of shared and lone pairs being as far apart as possible.

Table of Shapes # Pair Groups # Lone Pairs Molecular ShapeBond Angles 20Linear180 o Trigonal planar Bent 120 o <120 o Tetrahedron Trigonal pyramid Bent o <107 o <105 o

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

The properties of a substance depend in part on it’s polarity 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.

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