Unit 3: Bonding and Energy

Molecular dipole

The sum of all bond dipoles in a molecule, present if polar bonds are arranged asymmetrically.

Bond dipole

The unequal sharing of electrons between two atoms, shown with an arrow pointing towards the more electronegative atom.

Electronegativity

The tendency of an atom to attract electrons towards itself when part of a covalent bond.

Polyatomic ions

Charged particles made up of two or more covalently bonded elements that act as a single unit with an overall charge.

Asymmetric structures

Molecules that are not symmetrical; flipping them vertically would not yield the same structure.

Ionic bonds

Bond between a metal and a non-metal.

Covalent bonds

Bond between two non-metals.

Transition state

The highest point of energy in a reaction coordinate diagram, where bonds are breaking and forming.

Bond Enthalpy

The total amount of energy required to break down and reform bonds.

Chemical Potential Energy

Energy stored within the chemical bonds of substances.

Thermal Energy

Energy associated with the motion of particles.

Lewis Structures

Models that show the arrangement of valence electrons in molecules and polyatomic ions.

System vs. Surroundings

The system is the specific chemical process being studied; the surroundings include everything else.

Exothermic

A process that releases energy to the surroundings, often feeling hot to the touch.

Endothermic

A process that absorbs energy from the surroundings, often feeling cold to the touch.

Activation energy

The minimal amount of energy required to initiate a chemical reaction.

Enthalpy Change (▵H)

The difference in potential energy between reactants and products.

Lattice Energy

A measure of the strength of an ionic bond; higher lattice energy indicates stronger attractions.

Dissociation

The process in which an ionic bond breaks apart into individual ions when dissolved in water.

Physical change

An alteration in the form or state of a substance without changing its chemical properties.

Chemical change

A change that forms a new substance through the breaking and forming of chemical bonds.

Heat (q) formula

q = mcΔT, where m is mass, c is specific heat capacity, and ΔT is the change in temperature.

Stoichiometry and Enthalpy (ΔH)

Enthalpy changes are proportional to the amount of substance reacting, linked to the coefficients in balanced equations.

Reactants and Products in Reaction Coordinate Diagrams

Reactants are plotted higher than products in exothermic reactions and lower in endothermic reactions.

Activation Energy (E_a)

The energy hill that reactants must overcome, marked by the distance between reactants and the peak in the graph.

Transition State in Reaction Coordinate Diagrams

The peak of the curve, indicating the highest energy point where bonds are breaking and forming.