bond polarity and intramolecular forces

Chemical Bond

Forces that hold groups of atoms together and make them function as a unit; a bond forms if the energy of the compound is lower than that of the separated atoms.

Intramolecular Forces

Forces of attraction that hold atoms together within a molecule or compound; include covalent, ionic, and metallic bonds.

Coulomb's Law

Describes the strength of the electrostatic force between two charged particles; the force increases with greater charge and decreases with greater distance between particles.

Bond Length and Energy

Bonds become shorter and stronger as the number of bonds between two atoms increases; triple bonds are shorter and stronger than double or single bonds.

Covalent Bond

A type of intramolecular force where electrons are shared between atoms; can be polar (unequal sharing) or non-polar (equal sharing).

Ionic Bond

A type of intramolecular force where electrons are transferred from one atom to another, typically between metals and non-metals, resulting in oppositely charged ions.

Metallic Bond

A type of intramolecular force where electrons are free to move through a lattice of metal atoms, often described as a "sea of electrons."

Non-Polar Covalent Bond

An equal sharing of electrons between two atoms, resulting in no partial charges; typically occurs between identical atoms or atoms with similar electronegativities.

Polar Covalent Bond

An unequal sharing of electrons between atoms in a molecule; the more electronegative atom pulls electrons closer, resulting in partial charges (δ+ and δ−).

Electronegativity and Bond Type

The difference in electronegativity between two atoms determines bond type: >2.0 = Ionic, 0.5–1.9 = Polar Covalent, <0.4 = Non-Polar Covalent.

Determining Bond Polarity

If the bond is between a metal and a non-metal, it's ionic; between two different non-metals, it's polar covalent; between the same atom or a C-H bond, it's non-polar covalent.

Dipole Moment

Created in a polar covalent bond; a property of a molecule where there is a separation of charge, represented by an arrow pointing toward the partial negative side.

Polar Molecule

A molecule with a positive and a negative end; requires the molecule to contain polar bonds and be asymmetrical in shape.

Non-Polar Molecule

A molecule where the dipoles cancel out due to symmetry, resulting in no overall dipole moment; can have polar bonds but still be non-polar overall.

Asymmetrical Molecules

Molecules that lack symmetry; if they have polar bonds and no cancellation of dipoles, they are polar molecules.

Symmetrical Molecules

Molecules that are symmetrical; if they have polar bonds, the dipoles cancel out, resulting in a non-polar molecule.

Examples of Polar Molecules

H₂O, HCl, NH₃; these molecules have polar bonds and are asymmetrical, resulting in a net dipole moment.

Examples of Non-Polar Molecules

CO₂, BF₃, CCl₄; these molecules have polar bonds but are symmetrical, so the dipoles cancel out, resulting in no net dipole moment.

Practice with Dipoles

Draw the dipole arrows for the following bonds: H–S, F–C, C–Si, N–O; indicate the direction of electron pull based on electronegativity differences.

Summary of Bond Polarity

In a polar bond, one atom is more electronegative than the other; in a non-polar bond, both atoms have similar electronegativities; molecular polarity depends on both bond polarity and molecular symmetry.