Understanding Chemical Bonds and Reaction Types

Chemical Bonds and Atomic Structure

A chemical bond is the union between atoms. They are held together by electrostatic forces of nature. The unique chemical bond depends on the number of electrons that the atom holds in its outermost energy levels. Types of bonds include:

Covalent Bond

The union of atoms achieved by sharing electrons. The covalent bond may occur in:

Molecular Substances

• Insoluble in water
• Low melting point
• Gaseous, solid, or liquid state
• Do not conduct electricity

Atomic Substances

• Insoluble in all solvents
• Do not conduct electricity (except graphite)
• Very hard solids with high melting points

Ionic Bond (Salt Bridge)

Occurs between metals and nonmetals when they form electrically charged atoms: the cation (+) and the anion (-). The resulting ions have opposite charges, attract, and remain together. This results in ionic substances.

Ionic Substances Characteristics

• Solid state
• High melting point, hard, and fragile
• Some are soluble in water
• Do not conduct electricity in the solid state, but do conduct when molten or in solution
• Form crystal lattices (networks)

Metallic Bond

A bond between metal elements. It forms networks and is characterized by an ordered lattice of positive ions immersed in a 'sea' or cloud of very weakly attached electrons. This gives rise to metallic substances.

Metallic Substances Characteristics

• Most are solid
• High melting point
• Insoluble
• Malleable and ductile
• Conduct heat and electricity in both the solid and molten states

Fundamental Chemical Definitions

Crystal Lattice

A set of particles (atoms, positive or negative ions) arranged in a specific, repeating pattern throughout unlimited space.

Physical Change

When a substance undergoes a transformation that changes its state of aggregation or its appearance, but its chemical nature remains the same.

Chemical Change and Reaction

When a substance undergoes a transformation that fundamentally changes its chemical nature.

Exothermic Reactions

Reactions in which heat is released.

Endothermic Reactions

Reactions in which heat is absorbed.

Activation Energy

The initial energy that must be supplied to most reactions in order for them to start.

Synthesis Reaction

A reaction in which two or more substances combine to form more complex substances.

Decomposition Reaction

A reaction where one chemical substance breaks down into two or more simpler substances, which may be compounds or elements.